perlfunc


DESCRIPTION
       The functions in this section can serve as terms in an expression.
       They fall into two major categories: list operators and named unary
       operators.  These differ in their precedence relationship with a
       following comma.  (See the precedence table in perlop.)  List operators
       take more than one argument, while unary operators can never take more
       than one argument.  Thus, a comma terminates the argument of a unary
       operator, but merely separates the arguments of a list operator.  A
       unary operator generally provides a scalar context to its argument,
       while a list operator may provide either scalar or list contexts for
       its arguments.  If it does both, the scalar arguments will be first,
       and the list argument will follow.  (Note that there can ever be only
       one such list argument.)  For instance, splice() has three scalar
       arguments followed by a list, whereas gethostbyname() has four scalar
       arguments.

       In the syntax descriptions that follow, list operators that expect a
       list (and provide list context for the elements of the list) are shown
       with LIST as an argument.  Such a list may consist of any combination
       of scalar arguments or list values; the list values will be included in
       the list as if each individual element were interpolated at that point
       in the list, forming a longer single-dimensional list value.  Commas
       should separate elements of the LIST.

       Any function in the list below may be used either with or without
       parentheses around its arguments.  (The syntax descriptions omit the
       parentheses.)  If you use the parentheses, the simple (but occasionally
       surprising) rule is this: It looks like a function, therefore it is a
       function, and precedence doesn't matter.  Otherwise it's a list
       operator or unary operator, and precedence does matter.  And whitespace
       between the function and left parenthesis doesn't count--so you need to
       be careful sometimes:

           print 1+2+4;        # Prints 7.
           print(1+2) + 4;     # Prints 3.
           print (1+2)+4;      # Also prints 3!
           print +(1+2)+4;     # Prints 7.
           print ((1+2)+4);    # Prints 7.

       If you run Perl with the -w switch it can warn you about this.  For
       example, the third line above produces:

           print (...) interpreted as function at - line 1.
           Useless use of integer addition in void context at - line 1.

       A few functions take no arguments at all, and therefore work as neither
       unary nor list operators.  These include such functions as "time" and
       "endpwent".  For example, "time+86_400" always means "time() + 86_400".

       For functions that can be used in either a scalar or list context,
       nonabortive failure is generally indicated in a scalar context by
       returning the undefined value, and in a list context by returning the
       null list.
       A named array in scalar context is quite different from what would at
       first glance appear to be a list in scalar context.  You can't get a
       list like "(1,2,3)" into being in scalar context, because the compiler
       knows the context at compile time.  It would generate the scalar comma
       operator there, not the list construction version of the comma.  That
       means it was never a list to start with.

       In general, functions in Perl that serve as wrappers for system calls
       of the same name (like chown(2), fork(2), closedir(2), etc.) all return
       true when they succeed and "undef" otherwise, as is usually mentioned
       in the descriptions below.  This is different from the C interfaces,
       which return "-1" on failure.  Exceptions to this rule are "wait",
       "waitpid", and "syscall".  System calls also set the special $!
       variable on failure.  Other functions do not, except accidentally.

   Perl Functions by Category
       Here are Perl's functions (including things that look like functions,
       like some keywords and named operators) arranged by category.  Some
       functions appear in more than one place.

       Functions for SCALARs or strings
           "chomp", "chop", "chr", "crypt", "hex", "index", "lc", "lcfirst",
           "length", "oct", "ord", "pack", "q//", "qq//", "reverse", "rindex",
           "sprintf", "substr", "tr///", "uc", "ucfirst", "y///"

       Regular expressions and pattern matching
           "m//", "pos", "quotemeta", "s///", "split", "study", "qr//"

       Numeric functions
           "abs", "atan2", "cos", "exp", "hex", "int", "log", "oct", "rand",
           "sin", "sqrt", "srand"

       Functions for real @ARRAYs
           "pop", "push", "shift", "splice", "unshift"

       Functions for list data
           "grep", "join", "map", "qw//", "reverse", "sort", "unpack"

       Functions for real %HASHes
           "delete", "each", "exists", "keys", "values"

       Input and output functions
           "binmode", "close", "closedir", "dbmclose", "dbmopen", "die",
           "eof", "fileno", "flock", "format", "getc", "print", "printf",
           "read", "readdir", "rewinddir", "say", "seek", "seekdir", "select",
           "syscall", "sysread", "sysseek", "syswrite", "tell", "telldir",
           "truncate", "warn", "write"

       Functions for fixed length data or records
           "pack", "read", "syscall", "sysread", "syswrite", "unpack", "vec"

       Functions for filehandles, files, or directories
           "-X", "chdir", "chmod", "chown", "chroot", "fcntl", "glob",
           "ioctl", "link", "lstat", "mkdir", "open", "opendir", "readlink",

       Keywords related to scoping
           "caller", "import", "local", "my", "our", "state", "package", "use"

           ("state" is only available if the "state" feature is enabled. See
           feature.)

       Miscellaneous functions
           "defined", "dump", "eval", "formline", "local", "my", "our",
           "reset", "scalar", "state", "undef", "wantarray"

       Functions for processes and process groups
           "alarm", "exec", "fork", "getpgrp", "getppid", "getpriority",
           "kill", "pipe", "qx//", "setpgrp", "setpriority", "sleep",
           "system", "times", "wait", "waitpid"

       Keywords related to perl modules
           "do", "import", "no", "package", "require", "use"

       Keywords related to classes and object-orientation
           "bless", "dbmclose", "dbmopen", "package", "ref", "tie", "tied",
           "untie", "use"

       Low-level socket functions
           "accept", "bind", "connect", "getpeername", "getsockname",
           "getsockopt", "listen", "recv", "send", "setsockopt", "shutdown",
           "socket", "socketpair"

       System V interprocess communication functions
           "msgctl", "msgget", "msgrcv", "msgsnd", "semctl", "semget",
           "semop", "shmctl", "shmget", "shmread", "shmwrite"

       Fetching user and group info
           "endgrent", "endhostent", "endnetent", "endpwent", "getgrent",
           "getgrgid", "getgrnam", "getlogin", "getpwent", "getpwnam",
           "getpwuid", "setgrent", "setpwent"

       Fetching network info
           "endprotoent", "endservent", "gethostbyaddr", "gethostbyname",
           "gethostent", "getnetbyaddr", "getnetbyname", "getnetent",
           "getprotobyname", "getprotobynumber", "getprotoent",
           "getservbyname", "getservbyport", "getservent", "sethostent",
           "setnetent", "setprotoent", "setservent"

       Time-related functions
           "gmtime", "localtime", "time", "times"

       Functions new in perl5
           "abs", "bless", "break", "chomp", "chr", "continue", "default",
           "exists", "formline", "given", "glob", "import", "lc", "lcfirst",
           "lock", "map", "my", "no", "our", "prototype", "qr//", "qw//",
           "qx//", "readline", "readpipe", "ref", "sub"*, "sysopen", "tie",
           "tied", "uc", "ucfirst", "untie", "use", "when"

       "-X", "binmode", "chmod", "chown", "chroot", "crypt", "dbmclose",
       "dbmopen", "dump", "endgrent", "endhostent", "endnetent",
       "endprotoent", "endpwent", "endservent", "exec", "fcntl", "flock",
       "fork", "getgrent", "getgrgid", "gethostbyname", "gethostent",
       "getlogin", "getnetbyaddr", "getnetbyname", "getnetent", "getppid",
       "getpgrp", "getpriority", "getprotobynumber", "getprotoent",
       "getpwent", "getpwnam", "getpwuid", "getservbyport", "getservent",
       "getsockopt", "glob", "ioctl", "kill", "link", "lstat", "msgctl",
       "msgget", "msgrcv", "msgsnd", "open", "pipe", "readlink", "rename",
       "select", "semctl", "semget", "semop", "setgrent", "sethostent",
       "setnetent", "setpgrp", "setpriority", "setprotoent", "setpwent",
       "setservent", "setsockopt", "shmctl", "shmget", "shmread", "shmwrite",
       "socket", "socketpair", "stat", "symlink", "syscall", "sysopen",
       "system", "times", "truncate", "umask", "unlink", "utime", "wait",
       "waitpid"

       For more information about the portability of these functions, see
       perlport and other available platform-specific documentation.

   Alphabetical Listing of Perl Functions
       -X FILEHANDLE
       -X EXPR
       -X DIRHANDLE
       -X      A file test, where X is one of the letters listed below.  This
               unary operator takes one argument, either a filename, a
               filehandle, or a dirhandle, and tests the associated file to
               see if something is true about it.  If the argument is omitted,
               tests $_, except for "-t", which tests STDIN.  Unless otherwise
               documented, it returns 1 for true and '' for false, or the
               undefined value if the file doesn't exist.  Despite the funny
               names, precedence is the same as any other named unary
               operator.  The operator may be any of:

                   -r  File is readable by effective uid/gid.
                   -w  File is writable by effective uid/gid.
                   -x  File is executable by effective uid/gid.
                   -o  File is owned by effective uid.

                   -R  File is readable by real uid/gid.
                   -W  File is writable by real uid/gid.
                   -X  File is executable by real uid/gid.
                   -O  File is owned by real uid.

                   -e  File exists.
                   -z  File has zero size (is empty).
                   -s  File has nonzero size (returns size in bytes).

                   -f  File is a plain file.
                   -d  File is a directory.
                   -l  File is a symbolic link.
                   -p  File is a named pipe (FIFO), or Filehandle is a pipe.
                   -S  File is a socket.
                   -b  File is a block special file.
                   -c  File is a character special file.

               Example:

                   while (<>) {
                       chomp;
                       next unless -f $_;      # ignore specials
                       #...
                   }

               The interpretation of the file permission operators "-r", "-R",
               "-w", "-W", "-x", and "-X" is by default based solely on the
               mode of the file and the uids and gids of the user.  There may
               be other reasons you can't actually read, write, or execute the
               file: for example network filesystem access controls, ACLs
               (access control lists), read-only filesystems, and unrecognized
               executable formats.  Note that the use of these six specific
               operators to verify if some operation is possible is usually a
               mistake, because it may be open to race conditions.

               Also note that, for the superuser on the local filesystems, the
               "-r", "-R", "-w", and "-W" tests always return 1, and "-x" and
               "-X" return 1 if any execute bit is set in the mode.  Scripts
               run by the superuser may thus need to do a stat() to determine
               the actual mode of the file, or temporarily set their effective
               uid to something else.

               If you are using ACLs, there is a pragma called "filetest" that
               may produce more accurate results than the bare stat() mode
               bits.  When under the "use filetest 'access'" the above-
               mentioned filetests will test whether the permission can (not)
               be granted using the access() family of system calls.  Also
               note that the "-x" and "-X" may under this pragma return true
               even if there are no execute permission bits set (nor any extra
               execute permission ACLs).  This strangeness is due to the
               underlying system calls' definitions. Note also that, due to
               the implementation of "use filetest 'access'", the "_" special
               filehandle won't cache the results of the file tests when this
               pragma is in effect.  Read the documentation for the "filetest"
               pragma for more information.

               Note that "-s/a/b/" does not do a negated substitution.  Saying
               "-exp($foo)" still works as expected, however--only single
               letters following a minus are interpreted as file tests.

               The "-T" and "-B" switches work as follows.  The first block or
               so of the file is examined for odd characters such as strange
               control codes or characters with the high bit set.  If too many
               strange characters (>30%) are found, it's a "-B" file;
               otherwise it's a "-T" file.  Also, any file containing null in
               the first block is considered a binary file.  If "-T" or "-B"
               is used on a filehandle, the current IO buffer is examined
               rather than the first block.  Both "-T" and "-B" return true on
               a null file, or a file at EOF when testing a filehandle.
               Because you have to read a file to do the "-T" test, on most

                   print "Can do.\n" if -r $a || -w _ || -x _;

                   stat($filename);
                   print "Readable\n" if -r _;
                   print "Writable\n" if -w _;
                   print "Executable\n" if -x _;
                   print "Setuid\n" if -u _;
                   print "Setgid\n" if -g _;
                   print "Sticky\n" if -k _;
                   print "Text\n" if -T _;
                   print "Binary\n" if -B _;

               As of Perl 5.9.1, as a form of purely syntactic sugar, you can
               stack file test operators, in a way that "-f -w -x $file" is
               equivalent to "-x $file && -w _ && -f _". (This is only syntax
               fancy: if you use the return value of "-f $file" as an argument
               to another filetest operator, no special magic will happen.)

       abs VALUE
       abs     Returns the absolute value of its argument.  If VALUE is
               omitted, uses $_.

       accept NEWSOCKET,GENERICSOCKET
               Accepts an incoming socket connect, just as the accept(2)
               system call does.  Returns the packed address if it succeeded,
               false otherwise.  See the example in "Sockets: Client/Server
               Communication" in perlipc.

               On systems that support a close-on-exec flag on files, the flag
               will be set for the newly opened file descriptor, as determined
               by the value of $^F.  See "$^F" in perlvar.

       alarm SECONDS
       alarm   Arranges to have a SIGALRM delivered to this process after the
               specified number of wallclock seconds has elapsed.  If SECONDS
               is not specified, the value stored in $_ is used. (On some
               machines, unfortunately, the elapsed time may be up to one
               second less or more than you specified because of how seconds
               are counted, and process scheduling may delay the delivery of
               the signal even further.)

               Only one timer may be counting at once.  Each call disables the
               previous timer, and an argument of 0 may be supplied to cancel
               the previous timer without starting a new one.  The returned
               value is the amount of time remaining on the previous timer.

               For delays of finer granularity than one second, the
               Time::HiRes module (from CPAN, and starting from Perl 5.8 part
               of the standard distribution) provides ualarm().  You may also
               use Perl's four-argument version of select() leaving the first
               three arguments undefined, or you might be able to use the
               "syscall" interface to access setitimer(2) if your system
               supports it. See perlfaq8 for details.
                   eval {
                       local $SIG{ALRM} = sub { die "alarm\n" }; # NB: \n required
                       alarm $timeout;
                       $nread = sysread SOCKET, $buffer, $size;
                       alarm 0;
                   };
                   if ($@) {
                       die unless $@ eq "alarm\n";   # propagate unexpected errors
                       # timed out
                   }
                   else {
                       # didn't
                   }

               For more information see perlipc.

       atan2 Y,X
               Returns the arctangent of Y/X in the range -PI to PI.

               For the tangent operation, you may use the "Math::Trig::tan"
               function, or use the familiar relation:

                   sub tan { sin($_[0]) / cos($_[0])  }

               The return value for "atan2(0,0)" is implementation-defined;
               consult your atan2(3) manpage for more information.

       bind SOCKET,NAME
               Binds a network address to a socket, just as the bind system
               call does.  Returns true if it succeeded, false otherwise.
               NAME should be a packed address of the appropriate type for the
               socket.  See the examples in "Sockets: Client/Server
               Communication" in perlipc.

       binmode FILEHANDLE, LAYER
       binmode FILEHANDLE
               Arranges for FILEHANDLE to be read or written in "binary" or
               "text" mode on systems where the run-time libraries distinguish
               between binary and text files.  If FILEHANDLE is an expression,
               the value is taken as the name of the filehandle.  Returns true
               on success, otherwise it returns "undef" and sets $! (errno).

               On some systems (in general, DOS and Windows-based systems)
               binmode() is necessary when you're not working with a text
               file.  For the sake of portability it is a good idea to always
               use it when appropriate, and to never use it when it isn't
               appropriate.  Also, people can set their I/O to be by default
               UTF-8 encoded Unicode, not bytes.

               In other words: regardless of platform, use binmode() on binary
               data, like for example images.

               If LAYER is present it is a single string, but may contain
               multiple directives. The directives alter the behaviour of the

               The ":bytes", ":crlf", and ":utf8", and any other directives of
               the form ":...", are called I/O layers.  The "open" pragma can
               be used to establish default I/O layers.  See open.

               The LAYER parameter of the binmode() function is described as
               "DISCIPLINE" in "Programming Perl, 3rd Edition".  However,
               since the publishing of this book, by many known as "Camel
               III", the consensus of the naming of this functionality has
               moved from "discipline" to "layer".  All documentation of this
               version of Perl therefore refers to "layers" rather than to
               "disciplines".  Now back to the regularly scheduled
               documentation...

               To mark FILEHANDLE as UTF-8, use ":utf8" or ":encoding(utf8)".
               ":utf8" just marks the data as UTF-8 without further checking,
               while ":encoding(utf8)" checks the data for actually being
               valid UTF-8. More details can be found in PerlIO::encoding.

               In general, binmode() should be called after open() but before
               any I/O is done on the filehandle.  Calling binmode() will
               normally flush any pending buffered output data (and perhaps
               pending input data) on the handle.  An exception to this is the
               ":encoding" layer that changes the default character encoding
               of the handle, see open.  The ":encoding" layer sometimes needs
               to be called in mid-stream, and it doesn't flush the stream.
               The ":encoding" also implicitly pushes on top of itself the
               ":utf8" layer because internally Perl will operate on UTF-8
               encoded Unicode characters.

               The operating system, device drivers, C libraries, and Perl
               run-time system all work together to let the programmer treat a
               single character ("\n") as the line terminator, irrespective of
               the external representation.  On many operating systems, the
               native text file representation matches the internal
               representation, but on some platforms the external
               representation of "\n" is made up of more than one character.

               Mac OS, all variants of Unix, and Stream_LF files on VMS use a
               single character to end each line in the external
               representation of text (even though that single character is
               CARRIAGE RETURN on Mac OS and LINE FEED on Unix and most VMS
               files). In other systems like OS/2, DOS and the various flavors
               of MS-Windows your program sees a "\n" as a simple "\cJ", but
               what's stored in text files are the two characters "\cM\cJ".
               That means that, if you don't use binmode() on these systems,
               "\cM\cJ" sequences on disk will be converted to "\n" on input,
               and any "\n" in your program will be converted back to "\cM\cJ"
               on output.  This is what you want for text files, but it can be
               disastrous for binary files.

               Another consequence of using binmode() (on some systems) is
               that special end-of-file markers will be seen as part of the
               data stream.  For systems from the Microsoft family this means
               an object in the CLASSNAME package.  If CLASSNAME is omitted,
               the current package is used.  Because a "bless" is often the
               last thing in a constructor, it returns the reference for
               convenience.  Always use the two-argument version if a derived
               class might inherit the function doing the blessing.  See
               perltoot and perlobj for more about the blessing (and
               blessings) of objects.

               Consider always blessing objects in CLASSNAMEs that are mixed
               case.  Namespaces with all lowercase names are considered
               reserved for Perl pragmata.  Builtin types have all uppercase
               names. To prevent confusion, you may wish to avoid such package
               names as well.  Make sure that CLASSNAME is a true value.

               See "Perl Modules" in perlmod.

       break   Break out of a "given()" block.

               This keyword is enabled by the "switch" feature: see feature
               for more information.

       caller EXPR
       caller  Returns the context of the current subroutine call.  In scalar
               context, returns the caller's package name if there is a
               caller, that is, if we're in a subroutine or "eval" or
               "require", and the undefined value otherwise.  In list context,
               returns

                   # 0         1          2
                   ($package, $filename, $line) = caller;

               With EXPR, it returns some extra information that the debugger
               uses to print a stack trace.  The value of EXPR indicates how
               many call frames to go back before the current one.

                   #  0         1          2      3            4
                   ($package, $filename, $line, $subroutine, $hasargs,

                   #  5          6          7            8       9         10
                   $wantarray, $evaltext, $is_require, $hints, $bitmask, $hinthash)
                    = caller($i);

               Here $subroutine may be "(eval)" if the frame is not a
               subroutine call, but an "eval".  In such a case additional
               elements $evaltext and $is_require are set: $is_require is true
               if the frame is created by a "require" or "use" statement,
               $evaltext contains the text of the "eval EXPR" statement.  In
               particular, for an "eval BLOCK" statement, $subroutine is
               "(eval)", but $evaltext is undefined.  (Note also that each
               "use" statement creates a "require" frame inside an "eval EXPR"
               frame.)  $subroutine may also be "(unknown)" if this particular
               subroutine happens to have been deleted from the symbol table.
               $hasargs is true if a new instance of @_ was set up for the
               frame.  $hints and $bitmask contain pragmatic hints that the
               invoked.

               Be aware that the optimizer might have optimized call frames
               away before "caller" had a chance to get the information.  That
               means that caller(N) might not return information about the
               call frame you expect it do, for "N > 1".  In particular,
               @DB::args might have information from the previous time
               "caller" was called.

       chdir EXPR
       chdir FILEHANDLE
       chdir DIRHANDLE
       chdir   Changes the working directory to EXPR, if possible. If EXPR is
               omitted, changes to the directory specified by $ENV{HOME}, if
               set; if not, changes to the directory specified by
               $ENV{LOGDIR}. (Under VMS, the variable $ENV{SYS$LOGIN} is also
               checked, and used if it is set.) If neither is set, "chdir"
               does nothing. It returns true upon success, false otherwise.
               See the example under "die".

               On systems that support fchdir, you might pass a file handle or
               directory handle as argument.  On systems that don't support
               fchdir, passing handles produces a fatal error at run time.

       chmod LIST
               Changes the permissions of a list of files.  The first element
               of the list must be the numerical mode, which should probably
               be an octal number, and which definitely should not be a string
               of octal digits: 0644 is okay, '0644' is not.  Returns the
               number of files successfully changed.  See also "oct", if all
               you have is a string.

                   $cnt = chmod 0755, 'foo', 'bar';
                   chmod 0755, @executables;
                   $mode = '0644'; chmod $mode, 'foo';      # !!! sets mode to
                                                            # --w----r-T
                   $mode = '0644'; chmod oct($mode), 'foo'; # this is better
                   $mode = 0644;   chmod $mode, 'foo';      # this is best

               On systems that support fchmod, you might pass file handles
               among the files.  On systems that don't support fchmod, passing
               file handles produces a fatal error at run time.   The file
               handles must be passed as globs or references to be recognized.
               Barewords are considered file names.

                   open(my $fh, "<", "foo");
                   my $perm = (stat $fh)[2] & 07777;
                   chmod($perm | 0600, $fh);

               You can also import the symbolic "S_I*" constants from the
               Fcntl module:

                   use Fcntl ':mode';

               all trailing newlines from the string.  When in slurp mode ("$/
               = undef") or fixed-length record mode ($/ is a reference to an
               integer or the like, see perlvar) chomp() won't remove
               anything.  If VARIABLE is omitted, it chomps $_.  Example:

                   while (<>) {
                       chomp;  # avoid \n on last field
                       @array = split(/:/);
                       # ...
                   }

               If VARIABLE is a hash, it chomps the hash's values, but not its
               keys.

               You can actually chomp anything that's an lvalue, including an
               assignment:

                   chomp($cwd = `pwd`);
                   chomp($answer = <STDIN>);

               If you chomp a list, each element is chomped, and the total
               number of characters removed is returned.

               Note that parentheses are necessary when you're chomping
               anything that is not a simple variable.  This is because "chomp
               $cwd = `pwd`;" is interpreted as "(chomp $cwd) = `pwd`;",
               rather than as "chomp( $cwd = `pwd` )" which you might expect.
               Similarly, "chomp $a, $b" is interpreted as "chomp($a), $b"
               rather than as "chomp($a, $b)".

       chop VARIABLE
       chop( LIST )
       chop    Chops off the last character of a string and returns the
               character chopped.  It is much more efficient than "s/.$//s"
               because it neither scans nor copies the string.  If VARIABLE is
               omitted, chops $_.  If VARIABLE is a hash, it chops the hash's
               values, but not its keys.

               You can actually chop anything that's an lvalue, including an
               assignment.

               If you chop a list, each element is chopped.  Only the value of
               the last "chop" is returned.

               Note that "chop" returns the last character.  To return all but
               the last character, use "substr($string, 0, -1)".

               See also "chomp".

       chown LIST
               Changes the owner (and group) of a list of files.  The first
               two elements of the list must be the numeric uid and gid, in
               that order.  A value of -1 in either position is interpreted by
               most systems to leave that value unchanged.  Returns the number
               file:

                   print "User: ";
                   chomp($user = <STDIN>);
                   print "Files: ";
                   chomp($pattern = <STDIN>);

                   ($login,$pass,$uid,$gid) = getpwnam($user)
                       or die "$user not in passwd file";

                   @ary = glob($pattern);      # expand filenames
                   chown $uid, $gid, @ary;

               On most systems, you are not allowed to change the ownership of
               the file unless you're the superuser, although you should be
               able to change the group to any of your secondary groups.  On
               insecure systems, these restrictions may be relaxed, but this
               is not a portable assumption.  On POSIX systems, you can detect
               this condition this way:

                   use POSIX qw(sysconf _PC_CHOWN_RESTRICTED);
                   $can_chown_giveaway = not sysconf(_PC_CHOWN_RESTRICTED);

       chr NUMBER
       chr     Returns the character represented by that NUMBER in the
               character set.  For example, "chr(65)" is "A" in either ASCII
               or Unicode, and chr(0x263a) is a Unicode smiley face.

               Negative values give the Unicode replacement character
               (chr(0xfffd)), except under the bytes pragma, where low eight
               bits of the value (truncated to an integer) are used.

               If NUMBER is omitted, uses $_.

               For the reverse, use "ord".

               Note that characters from 128 to 255 (inclusive) are by default
               internally not encoded as UTF-8 for backward compatibility
               reasons.

               See perlunicode for more about Unicode.

       chroot FILENAME
       chroot  This function works like the system call by the same name: it
               makes the named directory the new root directory for all
               further pathnames that begin with a "/" by your process and all
               its children.  (It doesn't change your current working
               directory, which is unaffected.)  For security reasons, this
               call is restricted to the superuser.  If FILENAME is omitted,
               does a "chroot" to $_.

       close FILEHANDLE
       close   Closes the file or pipe associated with the file handle,
               flushes the IO buffers, and closes the system file descriptor.
               involved fails, or if the program exits with non-zero status.
               (If the only problem was that the program exited non-zero, $!
               will be set to 0.)  Closing a pipe also waits for the process
               executing on the pipe to complete, in case you want to look at
               the output of the pipe afterwards, and implicitly puts the exit
               status value of that command into $? and
               "${^CHILD_ERROR_NATIVE}".

               Prematurely closing the read end of a pipe (i.e. before the
               process writing to it at the other end has closed it) will
               result in a SIGPIPE being delivered to the writer.  If the
               other end can't handle that, be sure to read all the data
               before closing the pipe.

               Example:

                   open(OUTPUT, '|sort >foo')  # pipe to sort
                       or die "Can't start sort: $!";
                   #...                        # print stuff to output
                   close OUTPUT                # wait for sort to finish
                       or warn $! ? "Error closing sort pipe: $!"
                                  : "Exit status $? from sort";
                   open(INPUT, 'foo')          # get sort's results
                       or die "Can't open 'foo' for input: $!";

               FILEHANDLE may be an expression whose value can be used as an
               indirect filehandle, usually the real filehandle name.

       closedir DIRHANDLE
               Closes a directory opened by "opendir" and returns the success
               of that system call.

       connect SOCKET,NAME
               Attempts to connect to a remote socket, just as the connect
               system call does.  Returns true if it succeeded, false
               otherwise.  NAME should be a packed address of the appropriate
               type for the socket.  See the examples in "Sockets:
               Client/Server Communication" in perlipc.

       continue BLOCK
       continue
               "continue" is actually a flow control statement rather than a
               function.  If there is a "continue" BLOCK attached to a BLOCK
               (typically in a "while" or "foreach"), it is always executed
               just before the conditional is about to be evaluated again,
               just like the third part of a "for" loop in C.  Thus it can be
               used to increment a loop variable, even when the loop has been
               continued via the "next" statement (which is similar to the C
               "continue" statement).

               "last", "next", or "redo" may appear within a "continue" block.
               "last" and "redo" will behave as if they had been executed
               within the main block.  So will "next", but since it will
               execute a "continue" block, it may be more entertaining.
               using an empty one, logically enough.  In that case, "next"
               goes directly back to check the condition at the top of the
               loop.

               If the "switch" feature is enabled, "continue" is also a
               function that will break out of the current "when" or "default"
               block, and fall through to the next case. See feature and
               "Switch statements" in perlsyn for more information.

       cos EXPR
       cos     Returns the cosine of EXPR (expressed in radians).  If EXPR is
               omitted, takes cosine of $_.

               For the inverse cosine operation, you may use the
               "Math::Trig::acos()" function, or use this relation:

                   sub acos { atan2( sqrt(1 - $_[0] * $_[0]), $_[0] ) }

       crypt PLAINTEXT,SALT
               Creates a digest string exactly like the crypt(3) function in
               the C library (assuming that you actually have a version there
               that has not been extirpated as a potential munition).

               crypt() is a one-way hash function.  The PLAINTEXT and SALT is
               turned into a short string, called a digest, which is returned.
               The same PLAINTEXT and SALT will always return the same string,
               but there is no (known) way to get the original PLAINTEXT from
               the hash.  Small changes in the PLAINTEXT or SALT will result
               in large changes in the digest.

               There is no decrypt function.  This function isn't all that
               useful for cryptography (for that, look for Crypt modules on
               your nearby CPAN mirror) and the name "crypt" is a bit of a
               misnomer.  Instead it is primarily used to check if two pieces
               of text are the same without having to transmit or store the
               text itself.  An example is checking if a correct password is
               given.  The digest of the password is stored, not the password
               itself.  The user types in a password that is crypt()'d with
               the same salt as the stored digest.  If the two digests match
               the password is correct.

               When verifying an existing digest string you should use the
               digest as the salt (like "crypt($plain, $digest) eq $digest").
               The SALT used to create the digest is visible as part of the
               digest.  This ensures crypt() will hash the new string with the
               same salt as the digest.  This allows your code to work with
               the standard crypt and with more exotic implementations.  In
               other words, do not assume anything about the returned string
               itself, or how many bytes in the digest matter.

               Traditionally the result is a string of 13 bytes: two first
               bytes of the salt, followed by 11 bytes from the set
               "[./0-9A-Za-z]", and only the first eight bytes of PLAINTEXT
               mattered. But alternative hashing schemes (like MD5), higher

                   $pwd = (getpwuid($<))[1];

                   system "stty -echo";
                   print "Password: ";
                   chomp($word = <STDIN>);
                   print "\n";
                   system "stty echo";

                   if (crypt($word, $pwd) ne $pwd) {
                       die "Sorry...\n";
                   } else {
                       print "ok\n";
                   }

               Of course, typing in your own password to whoever asks you for
               it is unwise.

               The crypt function is unsuitable for hashing large quantities
               of data, not least of all because you can't get the information
               back.  Look at the Digest module for more robust algorithms.

               If using crypt() on a Unicode string (which potentially has
               characters with codepoints above 255), Perl tries to make sense
               of the situation by trying to downgrade (a copy of the string)
               the string back to an eight-bit byte string before calling
               crypt() (on that copy).  If that works, good.  If not, crypt()
               dies with "Wide character in crypt".

       dbmclose HASH
               [This function has been largely superseded by the "untie"
               function.]

               Breaks the binding between a DBM file and a hash.

       dbmopen HASH,DBNAME,MASK
               [This function has been largely superseded by the "tie"
               function.]

               This binds a dbm(3), ndbm(3), sdbm(3), gdbm(3), or Berkeley DB
               file to a hash.  HASH is the name of the hash.  (Unlike normal
               "open", the first argument is not a filehandle, even though it
               looks like one).  DBNAME is the name of the database (without
               the .dir or .pag extension if any).  If the database does not
               exist, it is created with protection specified by MASK (as
               modified by the "umask").  If your system supports only the
               older DBM functions, you may perform only one "dbmopen" in your
               program.  In older versions of Perl, if your system had neither
               DBM nor ndbm, calling "dbmopen" produced a fatal error; it now
               falls back to sdbm(3).

               If you don't have write access to the DBM file, you can only
               read hash variables, not set them.  If you want to test whether
               you can write, either use file tests or try setting a dummy

               See also AnyDBM_File for a more general description of the pros
               and cons of the various dbm approaches, as well as DB_File for
               a particularly rich implementation.

               You can control which DBM library you use by loading that
               library before you call dbmopen():

                   use DB_File;
                   dbmopen(%NS_Hist, "$ENV{HOME}/.netscape/history.db")
                       or die "Can't open netscape history file: $!";

       defined EXPR
       defined Returns a Boolean value telling whether EXPR has a value other
               than the undefined value "undef".  If EXPR is not present, $_
               will be checked.

               Many operations return "undef" to indicate failure, end of
               file, system error, uninitialized variable, and other
               exceptional conditions.  This function allows you to
               distinguish "undef" from other values.  (A simple Boolean test
               will not distinguish among "undef", zero, the empty string, and
               "0", which are all equally false.)  Note that since "undef" is
               a valid scalar, its presence doesn't necessarily indicate an
               exceptional condition: "pop" returns "undef" when its argument
               is an empty array, or when the element to return happens to be
               "undef".

               You may also use "defined(&func)" to check whether subroutine
               &func has ever been defined.  The return value is unaffected by
               any forward declarations of &func.  Note that a subroutine
               which is not defined may still be callable: its package may
               have an "AUTOLOAD" method that makes it spring into existence
               the first time that it is called -- see perlsub.

               Use of "defined" on aggregates (hashes and arrays) is
               deprecated.  It used to report whether memory for that
               aggregate has ever been allocated.  This behavior may disappear
               in future versions of Perl.  You should instead use a simple
               test for size:

                   if (@an_array) { print "has array elements\n" }
                   if (%a_hash)   { print "has hash members\n"   }

               When used on a hash element, it tells you whether the value is
               defined, not whether the key exists in the hash.  Use "exists"
               for the latter purpose.

               Examples:

                   print if defined $switch{'D'};
                   print "$val\n" while defined($val = pop(@ary));
                   die "Can't readlink $sym: $!"
                       unless defined($value = readlink $sym);

               zero characters long.  This is all very above-board and honest.
               When a function returns an undefined value, it's an admission
               that it couldn't give you an honest answer.  So you should use
               "defined" only when you're questioning the integrity of what
               you're trying to do.  At other times, a simple comparison to 0
               or "" is what you want.

               See also "undef", "exists", "ref".

       delete EXPR
               Given an expression that specifies a hash element, array
               element, hash slice, or array slice, deletes the specified
               element(s) from the hash or array.  In the case of an array, if
               the array elements happen to be at the end, the size of the
               array will shrink to the highest element that tests true for
               exists() (or 0 if no such element exists).

               Returns a list with the same number of elements as the number
               of elements for which deletion was attempted.  Each element of
               that list consists of either the value of the element deleted,
               or the undefined value.  In scalar context, this means that you
               get the value of the last element deleted (or the undefined
               value if that element did not exist).

                   %hash = (foo => 11, bar => 22, baz => 33);
                   $scalar = delete $hash{foo};             # $scalar is 11
                   $scalar = delete @hash{qw(foo bar)};     # $scalar is 22
                   @array  = delete @hash{qw(foo bar baz)}; # @array  is (undef,undef,33)

               Deleting from %ENV modifies the environment.  Deleting from a
               hash tied to a DBM file deletes the entry from the DBM file.
               Deleting from a "tie"d hash or array may not necessarily return
               anything.

               Deleting an array element effectively returns that position of
               the array to its initial, uninitialized state.  Subsequently
               testing for the same element with exists() will return false.
               Also, deleting array elements in the middle of an array will
               not shift the index of the elements after them down.  Use
               splice() for that.  See "exists".

               The following (inefficiently) deletes all the values of %HASH
               and @ARRAY:

                   foreach $key (keys %HASH) {
                       delete $HASH{$key};
                   }

                   foreach $index (0 .. $#ARRAY) {
                       delete $ARRAY[$index];
                   }

               And so do these:


               Note that the EXPR can be arbitrarily complicated as long as
               the final operation is a hash element, array element,  hash
               slice, or array slice lookup:

                   delete $ref->[$x][$y]{$key};
                   delete @{$ref->[$x][$y]}{$key1, $key2, @morekeys};

                   delete $ref->[$x][$y][$index];
                   delete @{$ref->[$x][$y]}[$index1, $index2, @moreindices];

       die LIST
               Outside an "eval", prints the value of LIST to "STDERR" and
               exits with the current value of $! (errno).  If $! is 0, exits
               with the value of "($? >> 8)" (backtick `command` status).  If
               "($? >> 8)" is 0, exits with 255.  Inside an "eval()," the
               error message is stuffed into $@ and the "eval" is terminated
               with the undefined value.  This makes "die" the way to raise an
               exception.

               Equivalent examples:

                   die "Can't cd to spool: $!\n" unless chdir '/usr/spool/news';
                   chdir '/usr/spool/news' or die "Can't cd to spool: $!\n"

               If the last element of LIST does not end in a newline, the
               current script line number and input line number (if any) are
               also printed, and a newline is supplied.  Note that the "input
               line number" (also known as "chunk") is subject to whatever
               notion of "line" happens to be currently in effect, and is also
               available as the special variable $..  See "$/" in perlvar and
               "$." in perlvar.

               Hint: sometimes appending ", stopped" to your message will
               cause it to make better sense when the string "at foo line 123"
               is appended.  Suppose you are running script "canasta".

                   die "/etc/games is no good";
                   die "/etc/games is no good, stopped";

               produce, respectively

                   /etc/games is no good at canasta line 123.
                   /etc/games is no good, stopped at canasta line 123.

               See also exit(), warn(), and the Carp module.

               If LIST is empty and $@ already contains a value (typically
               from a previous eval) that value is reused after appending
               "\t...propagated".  This is useful for propagating exceptions:

                   eval { ... };
                   die unless $@ =~ /Expected exception/;

               state about the nature of the exception.  Such a scheme is
               sometimes preferable to matching particular string values of $@
               using regular expressions.  Because $@ is a global variable,
               and eval() may be used within object implementations, care must
               be taken that analyzing the error object doesn't replace the
               reference in the global variable.  The easiest solution is to
               make a local copy of the reference before doing other
               manipulations.  Here's an example:

                   use Scalar::Util 'blessed';

                   eval { ... ; die Some::Module::Exception->new( FOO => "bar" ) };
                   if (my $ev_err = $@) {
                       if (blessed($ev_err) && $ev_err->isa("Some::Module::Exception")) {
                           # handle Some::Module::Exception
                       }
                       else {
                           # handle all other possible exceptions
                       }
                   }

               Because perl will stringify uncaught exception messages before
               displaying them, you may want to overload stringification
               operations on such custom exception objects.  See overload for
               details about that.

               You can arrange for a callback to be run just before the "die"
               does its deed, by setting the $SIG{__DIE__} hook.  The
               associated handler will be called with the error text and can
               change the error message, if it sees fit, by calling "die"
               again.  See "$SIG{expr}" in perlvar for details on setting %SIG
               entries, and "eval BLOCK" for some examples.  Although this
               feature was to be run only right before your program was to
               exit, this is not currently the case--the $SIG{__DIE__} hook is
               currently called even inside eval()ed blocks/strings!  If one
               wants the hook to do nothing in such situations, put

                       die @_ if $^S;

               as the first line of the handler (see "$^S" in perlvar).
               Because this promotes strange action at a distance, this
               counterintuitive behavior may be fixed in a future release.

       do BLOCK
               Not really a function.  Returns the value of the last command
               in the sequence of commands indicated by BLOCK.  When modified
               by the "while" or "until" loop modifier, executes the BLOCK
               once before testing the loop condition. (On other statements
               the loop modifiers test the conditional first.)

               "do BLOCK" does not count as a loop, so the loop control
               statements "next", "last", or "redo" cannot be used to leave or
               restart the block.  See perlsyn for alternative strategies.

               except that it's more efficient and concise, keeps track of the
               current filename for error messages, searches the @INC
               directories, and updates %INC if the file is found.  See
               "Predefined Names" in perlvar for these variables.  It also
               differs in that code evaluated with "do FILENAME" cannot see
               lexicals in the enclosing scope; "eval STRING" does.  It's the
               same, however, in that it does reparse the file every time you
               call it, so you probably don't want to do this inside a loop.

               If "do" cannot read the file, it returns undef and sets $! to
               the error.  If "do" can read the file but cannot compile it, it
               returns undef and sets an error message in $@.   If the file is
               successfully compiled, "do" returns the value of the last
               expression evaluated.

               Note that inclusion of library modules is better done with the
               "use" and "require" operators, which also do automatic error
               checking and raise an exception if there's a problem.

               You might like to use "do" to read in a program configuration
               file.  Manual error checking can be done this way:

                   # read in config files: system first, then user
                   for $file ("/share/prog/defaults.rc",
                              "$ENV{HOME}/.someprogrc")
                  {
                       unless ($return = do $file) {
                           warn "couldn't parse $file: $@" if $@;
                           warn "couldn't do $file: $!"    unless defined $return;
                           warn "couldn't run $file"       unless $return;
                       }
                   }

       dump LABEL
       dump    This function causes an immediate core dump.  See also the -u
               command-line switch in perlrun, which does the same thing.
               Primarily this is so that you can use the undump program (not
               supplied) to turn your core dump into an executable binary
               after having initialized all your variables at the beginning of
               the program.  When the new binary is executed it will begin by
               executing a "goto LABEL" (with all the restrictions that "goto"
               suffers).  Think of it as a goto with an intervening core dump
               and reincarnation.  If "LABEL" is omitted, restarts the program
               from the top.

               WARNING: Any files opened at the time of the dump will not be
               open any more when the program is reincarnated, with possible
               resulting confusion on the part of Perl.

               This function is now largely obsolete, mostly because it's very
               hard to convert a core file into an executable. That's why you
               should now invoke it as "CORE::dump()", if you don't want to be
               warned against a possible typo.

               reasons (see "Algorithmic Complexity Attacks" in perlsec).

               When the hash is entirely read, a null array is returned in
               list context (which when assigned produces a false (0) value),
               and "undef" in scalar context.  The next call to "each" after
               that will start iterating again.  There is a single iterator
               for each hash, shared by all "each", "keys", and "values"
               function calls in the program; it can be reset by reading all
               the elements from the hash, or by evaluating "keys HASH" or
               "values HASH".  If you add or delete elements of a hash while
               you're iterating over it, you may get entries skipped or
               duplicated, so don't.  Exception: It is always safe to delete
               the item most recently returned by "each()", which means that
               the following code will work:

                       while (($key, $value) = each %hash) {
                         print $key, "\n";
                         delete $hash{$key};   # This is safe
                       }

               The following prints out your environment like the printenv(1)
               program, only in a different order:

                   while (($key,$value) = each %ENV) {
                       print "$key=$value\n";
                   }

               See also "keys", "values" and "sort".

       eof FILEHANDLE
       eof ()
       eof     Returns 1 if the next read on FILEHANDLE will return end of
               file, or if FILEHANDLE is not open.  FILEHANDLE may be an
               expression whose value gives the real filehandle.  (Note that
               this function actually reads a character and then "ungetc"s it,
               so isn't very useful in an interactive context.)  Do not read
               from a terminal file (or call "eof(FILEHANDLE)" on it) after
               end-of-file is reached.  File types such as terminals may lose
               the end-of-file condition if you do.

               An "eof" without an argument uses the last file read.  Using
               "eof()" with empty parentheses is very different.  It refers to
               the pseudo file formed from the files listed on the command
               line and accessed via the "<>" operator.  Since "<>" isn't
               explicitly opened, as a normal filehandle is, an "eof()" before
               "<>" has been used will cause @ARGV to be examined to determine
               if input is available.   Similarly, an "eof()" after "<>" has
               returned end-of-file will assume you are processing another
               @ARGV list, and if you haven't set @ARGV, will read input from
               "STDIN"; see "I/O Operators" in perlop.

               In a "while (<>)" loop, "eof" or "eof(ARGV)" can be used to
               detect the end of each file, "eof()" will only detect the end
               of the last file.  Examples:
                           print "--------------\n";
                       }
                       print;
                       last if eof();          # needed if we're reading from a terminal
                   }

               Practical hint: you almost never need to use "eof" in Perl,
               because the input operators typically return "undef" when they
               run out of data, or if there was an error.

       eval EXPR
       eval BLOCK
       eval    In the first form, the return value of EXPR is parsed and
               executed as if it were a little Perl program.  The value of the
               expression (which is itself determined within scalar context)
               is first parsed, and if there weren't any errors, executed in
               the lexical context of the current Perl program, so that any
               variable settings or subroutine and format definitions remain
               afterwards.  Note that the value is parsed every time the
               "eval" executes.  If EXPR is omitted, evaluates $_.  This form
               is typically used to delay parsing and subsequent execution of
               the text of EXPR until run time.

               In the second form, the code within the BLOCK is parsed only
               once--at the same time the code surrounding the "eval" itself
               was parsed--and executed within the context of the current Perl
               program.  This form is typically used to trap exceptions more
               efficiently than the first (see below), while also providing
               the benefit of checking the code within BLOCK at compile time.

               The final semicolon, if any, may be omitted from the value of
               EXPR or within the BLOCK.

               In both forms, the value returned is the value of the last
               expression evaluated inside the mini-program; a return
               statement may be also used, just as with subroutines.  The
               expression providing the return value is evaluated in void,
               scalar, or list context, depending on the context of the "eval"
               itself.  See "wantarray" for more on how the evaluation context
               can be determined.

               If there is a syntax error or runtime error, or a "die"
               statement is executed, "eval" returns an undefined value in
               scalar context or an empty list in list context, and $@ is set
               to the error message.  If there was no error, $@ is guaranteed
               to be a null string.  Beware that using "eval" neither silences
               perl from printing warnings to STDERR, nor does it stuff the
               text of warning messages into $@.  To do either of those, you
               have to use the $SIG{__WARN__} facility, or turn off warnings
               inside the BLOCK or EXPR using "no warnings 'all'".  See
               "warn", perlvar, warnings and perllexwarn.

               Note that, because "eval" traps otherwise-fatal errors, it is
               useful for determining whether a particular feature (such as
               returned in $@.  Examples:

                   # make divide-by-zero nonfatal
                   eval { $answer = $a / $b; }; warn $@ if $@;

                   # same thing, but less efficient
                   eval '$answer = $a / $b'; warn $@ if $@;

                   # a compile-time error
                   eval { $answer = };                 # WRONG

                   # a run-time error
                   eval '$answer =';   # sets $@

               Using the "eval{}" form as an exception trap in libraries does
               have some issues.  Due to the current arguably broken state of
               "__DIE__" hooks, you may wish not to trigger any "__DIE__"
               hooks that user code may have installed.  You can use the
               "local $SIG{__DIE__}" construct for this purpose, as shown in
               this example:

                   # a very private exception trap for divide-by-zero
                   eval { local $SIG{'__DIE__'}; $answer = $a / $b; };
                   warn $@ if $@;

               This is especially significant, given that "__DIE__" hooks can
               call "die" again, which has the effect of changing their error
               messages:

                   # __DIE__ hooks may modify error messages
                   {
                      local $SIG{'__DIE__'} =
                             sub { (my $x = $_[0]) =~ s/foo/bar/g; die $x };
                      eval { die "foo lives here" };
                      print $@ if $@;                # prints "bar lives here"
                   }

               Because this promotes action at a distance, this
               counterintuitive behavior may be fixed in a future release.

               With an "eval", you should be especially careful to remember
               what's being looked at when:

                   eval $x;            # CASE 1
                   eval "$x";          # CASE 2

                   eval '$x';          # CASE 3
                   eval { $x };        # CASE 4

                   eval "\$$x++";      # CASE 5
                   $$x++;              # CASE 6

               Cases 1 and 2 above behave identically: they run the code
               contained in the variable $x.  (Although case 2 has misleading
               mask some but not all errors:

                   # alter $@ on nefarious repugnancy only
                   {
                      my $e;
                      {
                         local $@; # protect existing $@
                         eval { test_repugnancy() };
                         # $@ =~ /nefarious/ and die $@; # DOES NOT WORK
                         $@ =~ /nefarious/ and $e = $@;
                      }
                      die $e if defined $e
                   }

               "eval BLOCK" does not count as a loop, so the loop control
               statements "next", "last", or "redo" cannot be used to leave or
               restart the block.

               Note that as a very special case, an "eval ''" executed within
               the "DB" package doesn't see the usual surrounding lexical
               scope, but rather the scope of the first non-DB piece of code
               that called it. You don't normally need to worry about this
               unless you are writing a Perl debugger.

       exec LIST
       exec PROGRAM LIST
               The "exec" function executes a system command and never
               returns-- use "system" instead of "exec" if you want it to
               return.  It fails and returns false only if the command does
               not exist and it is executed directly instead of via your
               system's command shell (see below).

               Since it's a common mistake to use "exec" instead of "system",
               Perl warns you if there is a following statement which isn't
               "die", "warn", or "exit" (if "-w" is set  -  but you always do
               that).   If you really want to follow an "exec" with some other
               statement, you can use one of these styles to avoid the
               warning:

                   exec ('foo')   or print STDERR "couldn't exec foo: $!";
                   { exec ('foo') }; print STDERR "couldn't exec foo: $!";

               If there is more than one argument in LIST, or if LIST is an
               array with more than one value, calls execvp(3) with the
               arguments in LIST.  If there is only one scalar argument or an
               array with one element in it, the argument is checked for shell
               metacharacters, and if there are any, the entire argument is
               passed to the system's command shell for parsing (this is
               "/bin/sh -c" on Unix platforms, but varies on other platforms).
               If there are no shell metacharacters in the argument, it is
               split into words and passed directly to "execvp", which is more
               efficient.  Examples:

                   exec '/bin/echo', 'Your arguments are: ', @ARGV;

               or, more directly,

                   exec {'/bin/csh'} '-sh';    # pretend it's a login shell

               When the arguments get executed via the system shell, results
               will be subject to its quirks and capabilities.  See "`STRING`"
               in perlop for details.

               Using an indirect object with "exec" or "system" is also more
               secure.  This usage (which also works fine with system())
               forces interpretation of the arguments as a multivalued list,
               even if the list had just one argument.  That way you're safe
               from the shell expanding wildcards or splitting up words with
               whitespace in them.

                   @args = ( "echo surprise" );

                   exec @args;               # subject to shell escapes
                                               # if @args == 1
                   exec { $args[0] } @args;  # safe even with one-arg list

               The first version, the one without the indirect object, ran the
               echo program, passing it "surprise" an argument.  The second
               version didn't--it tried to run a program literally called
               "echo surprise", didn't find it, and set $? to a non-zero value
               indicating failure.

               Beginning with v5.6.0, Perl will attempt to flush all files
               opened for output before the exec, but this may not be
               supported on some platforms (see perlport).  To be safe, you
               may need to set $| ($AUTOFLUSH in English) or call the
               "autoflush()" method of "IO::Handle" on any open handles in
               order to avoid lost output.

               Note that "exec" will not call your "END" blocks, nor will it
               call any "DESTROY" methods in your objects.

       exists EXPR
               Given an expression that specifies a hash element or array
               element, returns true if the specified element in the hash or
               array has ever been initialized, even if the corresponding
               value is undefined.

                   print "Exists\n"    if exists $hash{$key};
                   print "Defined\n"   if defined $hash{$key};
                   print "True\n"      if $hash{$key};

                   print "Exists\n"    if exists $array[$index];
                   print "Defined\n"   if defined $array[$index];
                   print "True\n"      if $array[$index];

               A hash or array element can be true only if it's defined, and
               defined if it exists, but the reverse doesn't necessarily hold
                   print "Defined\n"   if defined &subroutine;

               Note that the EXPR can be arbitrarily complicated as long as
               the final operation is a hash or array key lookup or subroutine
               name:

                   if (exists $ref->{A}->{B}->{$key})  { }
                   if (exists $hash{A}{B}{$key})       { }

                   if (exists $ref->{A}->{B}->[$ix])   { }
                   if (exists $hash{A}{B}[$ix])        { }

                   if (exists &{$ref->{A}{B}{$key}})   { }

               Although the deepest nested array or hash will not spring into
               existence just because its existence was tested, any
               intervening ones will.  Thus "$ref->{"A"}" and
               "$ref->{"A"}->{"B"}" will spring into existence due to the
               existence test for the $key element above.  This happens
               anywhere the arrow operator is used, including even:

                   undef $ref;
                   if (exists $ref->{"Some key"})      { }
                   print $ref;             # prints HASH(0x80d3d5c)

               This surprising autovivification in what does not at first--or
               even second--glance appear to be an lvalue context may be fixed
               in a future release.

               Use of a subroutine call, rather than a subroutine name, as an
               argument to exists() is an error.

                   exists &sub;        # OK
                   exists &sub();      # Error

       exit EXPR
       exit    Evaluates EXPR and exits immediately with that value.
               Example:

                   $ans = <STDIN>;
                   exit 0 if $ans =~ /^[Xx]/;

               See also "die".  If EXPR is omitted, exits with 0 status.  The
               only universally recognized values for EXPR are 0 for success
               and 1 for error; other values are subject to interpretation
               depending on the environment in which the Perl program is
               running.  For example, exiting 69 (EX_UNAVAILABLE) from a
               sendmail incoming-mail filter will cause the mailer to return
               the item undelivered, but that's not true everywhere.

               Don't use "exit" to abort a subroutine if there's any chance
               that someone might want to trap whatever error happened.  Use
               "die" instead, which can be trapped by an "eval".

               Implements the fcntl(2) function.  You'll probably have to say

                   use Fcntl;

               first to get the correct constant definitions.  Argument
               processing and value return works just like "ioctl" below.  For
               example:

                   use Fcntl;
                   fcntl($filehandle, F_GETFL, $packed_return_buffer)
                       or die "can't fcntl F_GETFL: $!";

               You don't have to check for "defined" on the return from
               "fcntl".  Like "ioctl", it maps a 0 return from the system call
               into "0 but true" in Perl.  This string is true in boolean
               context and 0 in numeric context.  It is also exempt from the
               normal -w warnings on improper numeric conversions.

               Note that "fcntl" will produce a fatal error if used on a
               machine that doesn't implement fcntl(2).  See the Fcntl module
               or your fcntl(2) manpage to learn what functions are available
               on your system.

               Here's an example of setting a filehandle named "REMOTE" to be
               non-blocking at the system level.  You'll have to negotiate $|
               on your own, though.

                   use Fcntl qw(F_GETFL F_SETFL O_NONBLOCK);

                   $flags = fcntl(REMOTE, F_GETFL, 0)
                               or die "Can't get flags for the socket: $!\n";

                   $flags = fcntl(REMOTE, F_SETFL, $flags | O_NONBLOCK)
                               or die "Can't set flags for the socket: $!\n";

       fileno FILEHANDLE
               Returns the file descriptor for a filehandle, or undefined if
               the filehandle is not open.  This is mainly useful for
               constructing bitmaps for "select" and low-level POSIX tty-
               handling operations.  If FILEHANDLE is an expression, the value
               is taken as an indirect filehandle, generally its name.

               You can use this to find out whether two handles refer to the
               same underlying descriptor:

                   if (fileno(THIS) == fileno(THAT)) {
                       print "THIS and THAT are dups\n";
                   }

               (Filehandles connected to memory objects via new features of
               "open" may return undefined even though they are open.)

       flock FILEHANDLE,OPERATION
               Calls flock(2), or an emulation of it, on FILEHANDLE.  Returns
               details.  It's best to assume traditional behavior if you're
               writing portable programs.  (But if you're not, you should as
               always feel perfectly free to write for your own system's
               idiosyncrasies (sometimes called "features").  Slavish
               adherence to portability concerns shouldn't get in the way of
               your getting your job done.)

               OPERATION is one of LOCK_SH, LOCK_EX, or LOCK_UN, possibly
               combined with LOCK_NB.  These constants are traditionally
               valued 1, 2, 8 and 4, but you can use the symbolic names if you
               import them from the Fcntl module, either individually, or as a
               group using the ':flock' tag.  LOCK_SH requests a shared lock,
               LOCK_EX requests an exclusive lock, and LOCK_UN releases a
               previously requested lock.  If LOCK_NB is bitwise-or'ed with
               LOCK_SH or LOCK_EX then "flock" will return immediately rather
               than blocking waiting for the lock (check the return status to
               see if you got it).

               To avoid the possibility of miscoordination, Perl now flushes
               FILEHANDLE before locking or unlocking it.

               Note that the emulation built with lockf(3) doesn't provide
               shared locks, and it requires that FILEHANDLE be open with
               write intent.  These are the semantics that lockf(3)
               implements.  Most if not all systems implement lockf(3) in
               terms of fcntl(2) locking, though, so the differing semantics
               shouldn't bite too many people.

               Note that the fcntl(2) emulation of flock(3) requires that
               FILEHANDLE be open with read intent to use LOCK_SH and requires
               that it be open with write intent to use LOCK_EX.

               Note also that some versions of "flock" cannot lock things over
               the network; you would need to use the more system-specific
               "fcntl" for that.  If you like you can force Perl to ignore
               your system's flock(2) function, and so provide its own
               fcntl(2)-based emulation, by passing the switch "-Ud_flock" to
               the Configure program when you configure perl.

               Here's a mailbox appender for BSD systems.

                   use Fcntl qw(:flock SEEK_END); # import LOCK_* and SEEK_END constants

                   sub lock {
                       my ($fh) = @_;
                       flock($fh, LOCK_EX) or die "Cannot lock mailbox - $!\n";

                       # and, in case someone appended while we were waiting...
                       seek($fh, 0, SEEK_END) or die "Cannot seek - $!\n";
                   }

                   sub unlock {
                       my ($fh) = @_;
                       flock($fh, LOCK_UN) or die "Cannot unlock mailbox - $!\n";

               write servers.

               See also DB_File for other flock() examples.

       fork    Does a fork(2) system call to create a new process running the
               same program at the same point.  It returns the child pid to
               the parent process, 0 to the child process, or "undef" if the
               fork is unsuccessful.  File descriptors (and sometimes locks on
               those descriptors) are shared, while everything else is copied.
               On most systems supporting fork(), great care has gone into
               making it extremely efficient (for example, using copy-on-write
               technology on data pages), making it the dominant paradigm for
               multitasking over the last few decades.

               Beginning with v5.6.0, Perl will attempt to flush all files
               opened for output before forking the child process, but this
               may not be supported on some platforms (see perlport).  To be
               safe, you may need to set $| ($AUTOFLUSH in English) or call
               the "autoflush()" method of "IO::Handle" on any open handles in
               order to avoid duplicate output.

               If you "fork" without ever waiting on your children, you will
               accumulate zombies.  On some systems, you can avoid this by
               setting $SIG{CHLD} to "IGNORE".  See also perlipc for more
               examples of forking and reaping moribund children.

               Note that if your forked child inherits system file descriptors
               like STDIN and STDOUT that are actually connected by a pipe or
               socket, even if you exit, then the remote server (such as, say,
               a CGI script or a backgrounded job launched from a remote
               shell) won't think you're done.  You should reopen those to
               /dev/null if it's any issue.

       format  Declare a picture format for use by the "write" function.  For
               example:

                   format Something =
                       Test: @<<<<<<<< @||||| @>>>>>
                             $str,     $%,    '$' . int($num)
                   .

                   $str = "widget";
                   $num = $cost/$quantity;
                   $~ = 'Something';
                   write;

               See perlform for many details and examples.

       formline PICTURE,LIST
               This is an internal function used by "format"s, though you may
               call it, too.  It formats (see perlform) a list of values
               according to the contents of PICTURE, placing the output into
               the format output accumulator, $^A (or $ACCUMULATOR in
               English).  Eventually, when a "write" is done, the contents of
               examples.

       getc FILEHANDLE
       getc    Returns the next character from the input file attached to
               FILEHANDLE, or the undefined value at end of file, or if there
               was an error (in the latter case $! is set).  If FILEHANDLE is
               omitted, reads from STDIN.  This is not particularly efficient.
               However, it cannot be used by itself to fetch single characters
               without waiting for the user to hit enter.  For that, try
               something more like:

                   if ($BSD_STYLE) {
                       system "stty cbreak </dev/tty >/dev/tty 2>&1";
                   }
                   else {
                       system "stty", '-icanon', 'eol', "\001";
                   }

                   $key = getc(STDIN);

                   if ($BSD_STYLE) {
                       system "stty -cbreak </dev/tty >/dev/tty 2>&1";
                   }
                   else {
                       system "stty", 'icanon', 'eol', '^@'; # ASCII null
                   }
                   print "\n";

               Determination of whether $BSD_STYLE should be set is left as an
               exercise to the reader.

               The "POSIX::getattr" function can do this more portably on
               systems purporting POSIX compliance.  See also the
               "Term::ReadKey" module from your nearest CPAN site; details on
               CPAN can be found on "CPAN" in perlmodlib.

       getlogin
               This implements the C library function of the same name, which
               on most systems returns the current login from /etc/utmp, if
               any.  If null, use "getpwuid".

                   $login = getlogin || getpwuid($<) || "Kilroy";

               Do not consider "getlogin" for authentication: it is not as
               secure as "getpwuid".

       getpeername SOCKET
               Returns the packed sockaddr address of other end of the SOCKET
               connection.

                   use Socket;
                   $hersockaddr    = getpeername(SOCK);
                   ($port, $iaddr) = sockaddr_in($hersockaddr);
                   $herhostname    = gethostbyaddr($iaddr, AF_INET);

               Note for Linux users: on Linux, the C functions "getpid()" and
               "getppid()" return different values from different threads. In
               order to be portable, this behavior is not reflected by the
               perl-level function "getppid()", that returns a consistent
               value across threads. If you want to call the underlying
               "getppid()", you may use the CPAN module "Linux::Pid".

       getpriority WHICH,WHO
               Returns the current priority for a process, a process group, or
               a user.  (See getpriority(2).)  Will raise a fatal exception if
               used on a machine that doesn't implement getpriority(2).

       getpwnam NAME
       getgrnam NAME
       gethostbyname NAME
       getnetbyname NAME
       getprotobyname NAME
       getpwuid UID
       getgrgid GID
       getservbyname NAME,PROTO
       gethostbyaddr ADDR,ADDRTYPE
       getnetbyaddr ADDR,ADDRTYPE
       getprotobynumber NUMBER
       getservbyport PORT,PROTO
       getpwent
       getgrent
       gethostent
       getnetent
       getprotoent
       getservent
       setpwent
       setgrent
       sethostent STAYOPEN
       setnetent STAYOPEN
       setprotoent STAYOPEN
       setservent STAYOPEN
       endpwent
       endgrent
       endhostent
       endnetent
       endprotoent
       endservent
               These routines perform the same functions as their counterparts
               in the system library.  In list context, the return values from
               the various get routines are as follows:

                   ($name,$passwd,$uid,$gid,
                      $quota,$comment,$gcos,$dir,$shell,$expire) = getpw*
                   ($name,$passwd,$gid,$members) = getgr*
                   ($name,$aliases,$addrtype,$length,@addrs) = gethost*
                   ($name,$aliases,$addrtype,$net) = getnet*
                   ($name,$aliases,$proto) = getproto*
                   ($name,$aliases,$port,$proto) = getserv*

               In scalar context, you get the name, unless the function was a
               lookup by name, in which case you get the other thing, whatever
               it is.  (If the entry doesn't exist you get the undefined
               value.)  For example:

                   $uid   = getpwnam($name);
                   $name  = getpwuid($num);
                   $name  = getpwent();
                   $gid   = getgrnam($name);
                   $name  = getgrgid($num);
                   $name  = getgrent();
                   #etc.

               In getpw*() the fields $quota, $comment, and $expire are
               special cases in the sense that in many systems they are
               unsupported.  If the $quota is unsupported, it is an empty
               scalar.  If it is supported, it usually encodes the disk quota.
               If the $comment field is unsupported, it is an empty scalar.
               If it is supported it usually encodes some administrative
               comment about the user.  In some systems the $quota field may
               be $change or $age, fields that have to do with password aging.
               In some systems the $comment field may be $class.  The $expire
               field, if present, encodes the expiration period of the account
               or the password.  For the availability and the exact meaning of
               these fields in your system, please consult your getpwnam(3)
               documentation and your pwd.h file.  You can also find out from
               within Perl what your $quota and $comment fields mean and
               whether you have the $expire field by using the "Config" module
               and the values "d_pwquota", "d_pwage", "d_pwchange",
               "d_pwcomment", and "d_pwexpire".  Shadow password files are
               only supported if your vendor has implemented them in the
               intuitive fashion that calling the regular C library routines
               gets the shadow versions if you're running under privilege or
               if there exists the shadow(3) functions as found in System V
               (this includes Solaris and Linux.)  Those systems that
               implement a proprietary shadow password facility are unlikely
               to be supported.

               The $members value returned by getgr*() is a space separated
               list of the login names of the members of the group.

               For the gethost*() functions, if the "h_errno" variable is
               supported in C, it will be returned to you via $? if the
               function call fails.  The @addrs value returned by a successful
               call is a list of the raw addresses returned by the
               corresponding system library call.  In the Internet domain,
               each address is four bytes long and you can unpack it by saying
               something like:

                   ($a,$b,$c,$d) = unpack('W4',$addr[0]);

               The Socket library makes this slightly easier:

                   use Socket;
                       $ip_address = inet_ntoa($packed_ip);
                   }

               Make sure <gethostbyname()> is called in SCALAR context and
               that its return value is checked for definedness.

               If you get tired of remembering which element of the return
               list contains which return value, by-name interfaces are
               provided in standard modules: "File::stat", "Net::hostent",
               "Net::netent", "Net::protoent", "Net::servent", "Time::gmtime",
               "Time::localtime", and "User::grent".  These override the
               normal built-ins, supplying versions that return objects with
               the appropriate names for each field.  For example:

                  use File::stat;
                  use User::pwent;
                  $is_his = (stat($filename)->uid == pwent($whoever)->uid);

               Even though it looks like they're the same method calls (uid),
               they aren't, because a "File::stat" object is different from a
               "User::pwent" object.

       getsockname SOCKET
               Returns the packed sockaddr address of this end of the SOCKET
               connection, in case you don't know the address because you have
               several different IPs that the connection might have come in
               on.

                   use Socket;
                   $mysockaddr = getsockname(SOCK);
                   ($port, $myaddr) = sockaddr_in($mysockaddr);
                   printf "Connect to %s [%s]\n",
                      scalar gethostbyaddr($myaddr, AF_INET),
                      inet_ntoa($myaddr);

       getsockopt SOCKET,LEVEL,OPTNAME
               Queries the option named OPTNAME associated with SOCKET at a
               given LEVEL.  Options may exist at multiple protocol levels
               depending on the socket type, but at least the uppermost socket
               level SOL_SOCKET (defined in the "Socket" module) will exist.
               To query options at another level the protocol number of the
               appropriate protocol controlling the option should be supplied.
               For example, to indicate that an option is to be interpreted by
               the TCP protocol, LEVEL should be set to the protocol number of
               TCP, which you can get using getprotobyname.

               The call returns a packed string representing the requested
               socket option, or "undef" if there is an error (the error
               reason will be in $!). What exactly is in the packed string
               depends in the LEVEL and OPTNAME, consult your system
               documentation for details. A very common case however is that
               the option is an integer, in which case the result will be a
               packed integer which you can decode using unpack with the "i"
               (or "I") format.
                   print "Nagle's algorithm is turned ", $nodelay ? "off\n" : "on\n";

       glob EXPR
       glob    In list context, returns a (possibly empty) list of filename
               expansions on the value of EXPR such as the standard Unix shell
               /bin/csh would do. In scalar context, glob iterates through
               such filename expansions, returning undef when the list is
               exhausted. This is the internal function implementing the
               "<*.c>" operator, but you can use it directly. If EXPR is
               omitted, $_ is used.  The "<*.c>" operator is discussed in more
               detail in "I/O Operators" in perlop.

               Note that "glob" will split its arguments on whitespace,
               treating each segment as separate pattern.  As such, "glob('*.c
               *.h')" would match all files with a .c or .h extension.  The
               expression "glob('.* *')" would match all files in the current
               working directory.

               Beginning with v5.6.0, this operator is implemented using the
               standard "File::Glob" extension.  See File::Glob for details,
               including "bsd_glob" which does not treat whitespace as a
               pattern separator.

       gmtime EXPR
       gmtime  Works just like localtime but the returned values are localized
               for the standard Greenwich time zone.

               Note: when called in list context, $isdst, the last value
               returned by gmtime is always 0.  There is no Daylight Saving
               Time in GMT.

               See "gmtime" in perlport for portability concerns.

       goto LABEL
       goto EXPR
       goto &NAME
               The "goto-LABEL" form finds the statement labeled with LABEL
               and resumes execution there.  It may not be used to go into any
               construct that requires initialization, such as a subroutine or
               a "foreach" loop.  It also can't be used to go into a construct
               that is optimized away, or to get out of a block or subroutine
               given to "sort".  It can be used to go almost anywhere else
               within the dynamic scope, including out of subroutines, but
               it's usually better to use some other construct such as "last"
               or "die".  The author of Perl has never felt the need to use
               this form of "goto" (in Perl, that is--C is another matter).
               (The difference being that C does not offer named loops
               combined with loop control.  Perl does, and this replaces most
               structured uses of "goto" in other languages.)

               The "goto-EXPR" form expects a label name, whose scope will be
               resolved dynamically.  This allows for computed "goto"s per
               FORTRAN, but isn't necessarily recommended if you're optimizing
               for maintainability:
               subroutine are propagated to the other subroutine.)  After the
               "goto", not even "caller" will be able to tell that this
               routine was called first.

               NAME needn't be the name of a subroutine; it can be a scalar
               variable containing a code reference, or a block that evaluates
               to a code reference.

       grep BLOCK LIST
       grep EXPR,LIST
               This is similar in spirit to, but not the same as, grep(1) and
               its relatives.  In particular, it is not limited to using
               regular expressions.

               Evaluates the BLOCK or EXPR for each element of LIST (locally
               setting $_ to each element) and returns the list value
               consisting of those elements for which the expression evaluated
               to true.  In scalar context, returns the number of times the
               expression was true.

                   @foo = grep(!/^#/, @bar);    # weed out comments

               or equivalently,

                   @foo = grep {!/^#/} @bar;    # weed out comments

               Note that $_ is an alias to the list value, so it can be used
               to modify the elements of the LIST.  While this is useful and
               supported, it can cause bizarre results if the elements of LIST
               are not variables.  Similarly, grep returns aliases into the
               original list, much as a for loop's index variable aliases the
               list elements.  That is, modifying an element of a list
               returned by grep (for example, in a "foreach", "map" or another
               "grep") actually modifies the element in the original list.
               This is usually something to be avoided when writing clear
               code.

               If $_ is lexical in the scope where the "grep" appears (because
               it has been declared with "my $_") then, in addition to being
               locally aliased to the list elements, $_ keeps being lexical
               inside the block; i.e. it can't be seen from the outside,
               avoiding any potential side-effects.

               See also "map" for a list composed of the results of the BLOCK
               or EXPR.

       hex EXPR
       hex     Interprets EXPR as a hex string and returns the corresponding
               value.  (To convert strings that might start with either 0,
               "0x", or "0b", see "oct".)  If EXPR is omitted, uses $_.

                   print hex '0xAf'; # prints '175'
                   print hex 'aF';   # same

       index STR,SUBSTR,POSITION
       index STR,SUBSTR
               The index function searches for one string within another, but
               without the wildcard-like behavior of a full regular-expression
               pattern match.  It returns the position of the first occurrence
               of SUBSTR in STR at or after POSITION.  If POSITION is omitted,
               starts searching from the beginning of the string.  POSITION
               before the beginning of the string or after its end is treated
               as if it were the beginning or the end, respectively.  POSITION
               and the return value are based at 0 (or whatever you've set the
               $[ variable to--but don't do that).  If the substring is not
               found, "index" returns one less than the base, ordinarily "-1".

       int EXPR
       int     Returns the integer portion of EXPR.  If EXPR is omitted, uses
               $_.  You should not use this function for rounding: one because
               it truncates towards 0, and two because machine representations
               of floating point numbers can sometimes produce
               counterintuitive results.  For example, "int(-6.725/0.025)"
               produces -268 rather than the correct -269; that's because it's
               really more like -268.99999999999994315658 instead.  Usually,
               the "sprintf", "printf", or the "POSIX::floor" and
               "POSIX::ceil" functions will serve you better than will int().

       ioctl FILEHANDLE,FUNCTION,SCALAR
               Implements the ioctl(2) function.  You'll probably first have
               to say

                   require "sys/ioctl.ph";     # probably in $Config{archlib}/sys/ioctl.ph

               to get the correct function definitions.  If sys/ioctl.ph
               doesn't exist or doesn't have the correct definitions you'll
               have to roll your own, based on your C header files such as
               <sys/ioctl.h>.  (There is a Perl script called h2ph that comes
               with the Perl kit that may help you in this, but it's
               nontrivial.)  SCALAR will be read and/or written depending on
               the FUNCTION--a pointer to the string value of SCALAR will be
               passed as the third argument of the actual "ioctl" call.  (If
               SCALAR has no string value but does have a numeric value, that
               value will be passed rather than a pointer to the string value.
               To guarantee this to be true, add a 0 to the scalar before
               using it.)  The "pack" and "unpack" functions may be needed to
               manipulate the values of structures used by "ioctl".

               The return value of "ioctl" (and "fcntl") is as follows:

                       if OS returns:          then Perl returns:
                           -1                    undefined value
                            0                  string "0 but true"
                       anything else               that number

               Thus Perl returns true on success and false on failure, yet you
               can still easily determine the actual value returned by the
               operating system:
                   $rec = join(':', $login,$passwd,$uid,$gid,$gcos,$home,$shell);

               Beware that unlike "split", "join" doesn't take a pattern as
               its first argument.  Compare "split".

       keys HASH
               Returns a list consisting of all the keys of the named hash.
               (In scalar context, returns the number of keys.)

               The keys are returned in an apparently random order.  The
               actual random order is subject to change in future versions of
               perl, but it is guaranteed to be the same order as either the
               "values" or "each" function produces (given that the hash has
               not been modified).  Since Perl 5.8.1 the ordering is different
               even between different runs of Perl for security reasons (see
               "Algorithmic Complexity Attacks" in perlsec).

               As a side effect, calling keys() resets the HASH's internal
               iterator (see "each").  In particular, calling keys() in void
               context resets the iterator with no other overhead.

               Here is yet another way to print your environment:

                   @keys = keys %ENV;
                   @values = values %ENV;
                   while (@keys) {
                       print pop(@keys), '=', pop(@values), "\n";
                   }

               or how about sorted by key:

                   foreach $key (sort(keys %ENV)) {
                       print $key, '=', $ENV{$key}, "\n";
                   }

               The returned values are copies of the original keys in the
               hash, so modifying them will not affect the original hash.
               Compare "values".

               To sort a hash by value, you'll need to use a "sort" function.
               Here's a descending numeric sort of a hash by its values:

                   foreach $key (sort { $hash{$b} <=> $hash{$a} } keys %hash) {
                       printf "%4d %s\n", $hash{$key}, $key;
                   }

               As an lvalue "keys" allows you to increase the number of hash
               buckets allocated for the given hash.  This can gain you a
               measure of efficiency if you know the hash is going to get big.
               (This is similar to pre-extending an array by assigning a
               larger number to $#array.)  If you say

                   keys %hash = 200;

               Sends a signal to a list of processes.  Returns the number of
               processes successfully signaled (which is not necessarily the
               same as the number actually killed).

                   $cnt = kill 1, $child1, $child2;
                   kill 9, @goners;

               If SIGNAL is zero, no signal is sent to the process, but the
               kill(2) system call will check whether it's possible to send a
               signal to it (that means, to be brief, that the process is
               owned by the same user, or we are the super-user).  This is a
               useful way to check that a child process is alive (even if only
               as a zombie) and hasn't changed its UID.  See perlport for
               notes on the portability of this construct.

               Unlike in the shell, if SIGNAL is negative, it kills process
               groups instead of processes.  (On System V, a negative PROCESS
               number will also kill process groups, but that's not portable.)
               That means you usually want to use positive not negative
               signals.  You may also use a signal name in quotes.

               See "Signals" in perlipc for more details.

       last LABEL
       last    The "last" command is like the "break" statement in C (as used
               in loops); it immediately exits the loop in question.  If the
               LABEL is omitted, the command refers to the innermost enclosing
               loop.  The "continue" block, if any, is not executed:

                   LINE: while (<STDIN>) {
                       last LINE if /^$/;      # exit when done with header
                       #...
                   }

               "last" cannot be used to exit a block which returns a value
               such as "eval {}", "sub {}" or "do {}", and should not be used
               to exit a grep() or map() operation.

               Note that a block by itself is semantically identical to a loop
               that executes once.  Thus "last" can be used to effect an early
               exit out of such a block.

               See also "continue" for an illustration of how "last", "next",
               and "redo" work.

       lc EXPR
       lc      Returns a lowercased version of EXPR.  This is the internal
               function implementing the "\L" escape in double-quoted strings.
               Respects current LC_CTYPE locale if "use locale" in force.  See
               perllocale and perlunicode for more details about locale and
               Unicode support.

               If EXPR is omitted, uses $_.

               used on an entire array or hash to find out how many elements
               these have.  For that, use "scalar @array" and "scalar keys
               %hash" respectively.

               Note the characters: if the EXPR is in Unicode, you will get
               the number of characters, not the number of bytes.  To get the
               length of the internal string in bytes, use
               "bytes::length(EXPR)", see bytes.  Note that the internal
               encoding is variable, and the number of bytes usually
               meaningless.  To get the number of bytes that the string would
               have when encoded as UTF-8, use
               "length(Encoding::encode_utf8(EXPR))".

       link OLDFILE,NEWFILE
               Creates a new filename linked to the old filename.  Returns
               true for success, false otherwise.

       listen SOCKET,QUEUESIZE
               Does the same thing that the listen system call does.  Returns
               true if it succeeded, false otherwise.  See the example in
               "Sockets: Client/Server Communication" in perlipc.

       local EXPR
               You really probably want to be using "my" instead, because
               "local" isn't what most people think of as "local".  See
               "Private Variables via my()" in perlsub for details.

               A local modifies the listed variables to be local to the
               enclosing block, file, or eval.  If more than one value is
               listed, the list must be placed in parentheses.  See "Temporary
               Values via local()" in perlsub for details, including issues
               with tied arrays and hashes.

       localtime EXPR
       localtime
               Converts a time as returned by the time function to a 9-element
               list with the time analyzed for the local time zone.  Typically
               used as follows:

                   #  0    1    2     3     4    5     6     7     8
                   ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
                                                               localtime(time);

               All list elements are numeric, and come straight out of the C
               `struct tm'.  $sec, $min, and $hour are the seconds, minutes,
               and hours of the specified time.

               $mday is the day of the month, and $mon is the month itself, in
               the range 0..11 with 0 indicating January and 11 indicating
               December.  This makes it easy to get a month name from a list:

                   my @abbr = qw( Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec );
                   print "$abbr[$mon] $mday";
                   # $mon=9, $mday=18 gives "Oct 18"
                   $year = sprintf("%02d", $year % 100);

               $wday is the day of the week, with 0 indicating Sunday and 3
               indicating Wednesday.  $yday is the day of the year, in the
               range 0..364 (or 0..365 in leap years.)

               $isdst is true if the specified time occurs during Daylight
               Saving Time, false otherwise.

               If EXPR is omitted, "localtime()" uses the current time (as
               returned by time(3)).

               In scalar context, "localtime()" returns the ctime(3) value:

                   $now_string = localtime;  # e.g., "Thu Oct 13 04:54:34 1994"

               This scalar value is not locale dependent but is a Perl
               builtin. For GMT instead of local time use the "gmtime"
               builtin. See also the "Time::Local" module (to convert the
               second, minutes, hours, ... back to the integer value returned
               by time()), and the POSIX module's strftime(3) and mktime(3)
               functions.

               To get somewhat similar but locale dependent date strings, set
               up your locale environment variables appropriately (please see
               perllocale) and try for example:

                   use POSIX qw(strftime);
                   $now_string = strftime "%a %b %e %H:%M:%S %Y", localtime;
                   # or for GMT formatted appropriately for your locale:
                   $now_string = strftime "%a %b %e %H:%M:%S %Y", gmtime;

               Note that the %a and %b, the short forms of the day of the week
               and the month of the year, may not necessarily be three
               characters wide.

               See "localtime" in perlport for portability concerns.

               The Time::gmtime and Time::localtime modules provides a
               convenient, by-name access mechanism to the gmtime() and
               localtime() functions, respectively.

               For a comprehensive date and time representation look at the
               DateTime module on CPAN.

       lock THING
               This function places an advisory lock on a shared variable, or
               referenced object contained in THING until the lock goes out of
               scope.

               lock() is a "weak keyword" : this means that if you've defined
               a function by this name (before any calls to it), that function
               will be called instead. (However, if you've said "use threads",
               lock() is always a keyword.) See threads.

               See also "exp" for the inverse operation.

       lstat EXPR
       lstat   Does the same thing as the "stat" function (including setting
               the special "_" filehandle) but stats a symbolic link instead
               of the file the symbolic link points to.  If symbolic links are
               unimplemented on your system, a normal "stat" is done.  For
               much more detailed information, please see the documentation
               for "stat".

               If EXPR is omitted, stats $_.

       m//     The match operator.  See "Regexp Quote-Like Operators" in
               perlop.

       map BLOCK LIST
       map EXPR,LIST
               Evaluates the BLOCK or EXPR for each element of LIST (locally
               setting $_ to each element) and returns the list value composed
               of the results of each such evaluation.  In scalar context,
               returns the total number of elements so generated.  Evaluates
               BLOCK or EXPR in list context, so each element of LIST may
               produce zero, one, or more elements in the returned value.

                   @chars = map(chr, @nums);

               translates a list of numbers to the corresponding characters.
               And

                   %hash = map { get_a_key_for($_) => $_ } @array;

               is just a funny way to write

                   %hash = ();
                   foreach (@array) {
                       $hash{get_a_key_for($_)} = $_;
                   }

               Note that $_ is an alias to the list value, so it can be used
               to modify the elements of the LIST.  While this is useful and
               supported, it can cause bizarre results if the elements of LIST
               are not variables.  Using a regular "foreach" loop for this
               purpose would be clearer in most cases.  See also "grep" for an
               array composed of those items of the original list for which
               the BLOCK or EXPR evaluates to true.

               If $_ is lexical in the scope where the "map" appears (because
               it has been declared with "my $_"), then, in addition to being
               locally aliased to the list elements, $_ keeps being lexical
               inside the block; that is, it can't be seen from the outside,
               avoiding any potential side-effects.

               "{" starts both hash references and blocks, so "map { ..."
                   %hash = map { ("\L$_", 1) } @array  # this also works
                   %hash = map {  lc($_), 1  } @array  # as does this.
                   %hash = map +( lc($_), 1 ), @array  # this is EXPR and works!

                   %hash = map  ( lc($_), 1 ), @array  # evaluates to (1, @array)

               or to force an anon hash constructor use "+{":

                  @hashes = map +{ lc($_), 1 }, @array # EXPR, so needs , at end

               and you get list of anonymous hashes each with only 1 entry.

       mkdir FILENAME,MASK
       mkdir FILENAME
       mkdir   Creates the directory specified by FILENAME, with permissions
               specified by MASK (as modified by "umask").  If it succeeds it
               returns true, otherwise it returns false and sets $! (errno).
               If omitted, MASK defaults to 0777. If omitted, FILENAME
               defaults to $_.

               In general, it is better to create directories with permissive
               MASK, and let the user modify that with their "umask", than it
               is to supply a restrictive MASK and give the user no way to be
               more permissive.  The exceptions to this rule are when the file
               or directory should be kept private (mail files, for instance).
               The perlfunc(1) entry on "umask" discusses the choice of MASK
               in more detail.

               Note that according to the POSIX 1003.1-1996 the FILENAME may
               have any number of trailing slashes.  Some operating and
               filesystems do not get this right, so Perl automatically
               removes all trailing slashes to keep everyone happy.

               In order to recursively create a directory structure look at
               the "mkpath" function of the File::Path module.

       msgctl ID,CMD,ARG
               Calls the System V IPC function msgctl(2).  You'll probably
               have to say

                   use IPC::SysV;

               first to get the correct constant definitions.  If CMD is
               "IPC_STAT", then ARG must be a variable that will hold the
               returned "msqid_ds" structure.  Returns like "ioctl": the
               undefined value for error, "0 but true" for zero, or the actual
               return value otherwise.  See also "SysV IPC" in perlipc,
               "IPC::SysV", and "IPC::Semaphore" documentation.

       msgget KEY,FLAGS
               Calls the System V IPC function msgget(2).  Returns the message
               queue id, or the undefined value if there is an error.  See
               also "SysV IPC" in perlipc and "IPC::SysV" and "IPC::Msg"
               documentation.

       msgsnd ID,MSG,FLAGS
               Calls the System V IPC function msgsnd to send the message MSG
               to the message queue ID.  MSG must begin with the native long
               integer message type, and be followed by the length of the
               actual message, and finally the message itself.  This kind of
               packing can be achieved with "pack("l! a*", $type, $message)".
               Returns true if successful, or false if there is an error.  See
               also "IPC::SysV" and "IPC::SysV::Msg" documentation.

       my EXPR
       my TYPE EXPR
       my EXPR : ATTRS
       my TYPE EXPR : ATTRS
               A "my" declares the listed variables to be local (lexically) to
               the enclosing block, file, or "eval".  If more than one value
               is listed, the list must be placed in parentheses.

               The exact semantics and interface of TYPE and ATTRS are still
               evolving.  TYPE is currently bound to the use of "fields"
               pragma, and attributes are handled using the "attributes"
               pragma, or starting from Perl 5.8.0 also via the
               "Attribute::Handlers" module.  See "Private Variables via my()"
               in perlsub for details, and fields, attributes, and
               Attribute::Handlers.

       next LABEL
       next    The "next" command is like the "continue" statement in C; it
               starts the next iteration of the loop:

                   LINE: while (<STDIN>) {
                       next LINE if /^#/;      # discard comments
                       #...
                   }

               Note that if there were a "continue" block on the above, it
               would get executed even on discarded lines.  If the LABEL is
               omitted, the command refers to the innermost enclosing loop.

               "next" cannot be used to exit a block which returns a value
               such as "eval {}", "sub {}" or "do {}", and should not be used
               to exit a grep() or map() operation.

               Note that a block by itself is semantically identical to a loop
               that executes once.  Thus "next" will exit such a block early.

               See also "continue" for an illustration of how "last", "next",
               and "redo" work.

       no Module VERSION LIST
       no Module VERSION
       no Module LIST
       no Module
       no VERSION
               See the "use" function, of which "no" is the opposite.
               If EXPR is omitted, uses $_.   To go the other way (produce a
               number in octal), use sprintf() or printf():

                   $perms = (stat("filename"))[2] & 07777;
                   $oct_perms = sprintf "%lo", $perms;

               The oct() function is commonly used when a string such as 644
               needs to be converted into a file mode, for example. (Although
               perl will automatically convert strings into numbers as needed,
               this automatic conversion assumes base 10.)

       open FILEHANDLE,EXPR
       open FILEHANDLE,MODE,EXPR
       open FILEHANDLE,MODE,EXPR,LIST
       open FILEHANDLE,MODE,REFERENCE
       open FILEHANDLE
               Opens the file whose filename is given by EXPR, and associates
               it with FILEHANDLE.

               Simple examples to open a file for reading:

                   open(my $fh, '<', "input.txt") or die $!;

               and for writing:

                   open(my $fh, '>', "output.txt") or die $!;

               (The following is a comprehensive reference to open(): for a
               gentler introduction you may consider perlopentut.)

               If FILEHANDLE is an undefined scalar variable (or array or hash
               element) the variable is assigned a reference to a new
               anonymous filehandle, otherwise if FILEHANDLE is an expression,
               its value is used as the name of the real filehandle wanted.
               (This is considered a symbolic reference, so "use strict
               'refs'" should not be in effect.)

               If EXPR is omitted, the scalar variable of the same name as the
               FILEHANDLE contains the filename.  (Note that lexical
               variables--those declared with "my"--will not work for this
               purpose; so if you're using "my", specify EXPR in your call to
               open.)

               If three or more arguments are specified then the mode of
               opening and the file name are separate. If MODE is '<' or
               nothing, the file is opened for input.  If MODE is '>', the
               file is truncated and opened for output, being created if
               necessary.  If MODE is '>>', the file is opened for appending,
               again being created if necessary.

               You can put a '+' in front of the '>' or '<' to indicate that
               you want both read and write access to the file; thus '+<' is
               almost always preferred for read/write updates--the '+>' mode
               would clobber the file first.  You can't usually use either

               If the filename begins with '|', the filename is interpreted as
               a command to which output is to be piped, and if the filename
               ends with a '|', the filename is interpreted as a command which
               pipes output to us.  See "Using open() for IPC" in perlipc for
               more examples of this.  (You are not allowed to "open" to a
               command that pipes both in and out, but see IPC::Open2,
               IPC::Open3, and "Bidirectional Communication with Another
               Process" in perlipc for alternatives.)

               For three or more arguments if MODE is '|-', the filename is
               interpreted as a command to which output is to be piped, and if
               MODE is '-|', the filename is interpreted as a command which
               pipes output to us.  In the 2-arguments (and 1-argument) form
               one should replace dash ('-') with the command.  See "Using
               open() for IPC" in perlipc for more examples of this.  (You are
               not allowed to "open" to a command that pipes both in and out,
               but see IPC::Open2, IPC::Open3, and "Bidirectional
               Communication" in perlipc for alternatives.)

               In the three-or-more argument form of pipe opens, if LIST is
               specified (extra arguments after the command name) then LIST
               becomes arguments to the command invoked if the platform
               supports it.  The meaning of "open" with more than three
               arguments for non-pipe modes is not yet specified. Experimental
               "layers" may give extra LIST arguments meaning.

               In the 2-arguments (and 1-argument) form opening '-' opens
               STDIN and opening '>-' opens STDOUT.

               You may use the three-argument form of open to specify IO
               "layers" (sometimes also referred to as "disciplines") to be
               applied to the handle that affect how the input and output are
               processed (see open and PerlIO for more details). For example

                 open(my $fh, "<:encoding(UTF-8)", "file")

               will open the UTF-8 encoded file containing Unicode characters,
               see perluniintro. Note that if layers are specified in the
               three-arg form then default layers stored in ${^OPEN} (see
               perlvar; usually set by the open pragma or the switch -CioD)
               are ignored.

               Open returns nonzero upon success, the undefined value
               otherwise.  If the "open" involved a pipe, the return value
               happens to be the pid of the subprocess.

               If you're running Perl on a system that distinguishes between
               text files and binary files, then you should check out
               "binmode" for tips for dealing with this.  The key distinction
               between systems that need "binmode" and those that don't is
               their text file formats.  Systems like Unix, Mac OS, and Plan
               9, which delimit lines with a single character, and which
               encode that character in C as "\n", do not need "binmode".  The
               third argument being "undef":

                   open(my $tmp, "+>", undef) or die ...

               opens a filehandle to an anonymous temporary file.  Also using
               "+<" works for symmetry, but you really should consider writing
               something to the temporary file first.  You will need to seek()
               to do the reading.

               Since v5.8.0, perl has built using PerlIO by default.  Unless
               you've changed this (i.e. Configure -Uuseperlio), you can open
               file handles to "in memory" files held in Perl scalars via:

                   open($fh, '>', \$variable) || ..

               Though if you try to re-open "STDOUT" or "STDERR" as an "in
               memory" file, you have to close it first:

                   close STDOUT;
                   open STDOUT, '>', \$variable or die "Can't open STDOUT: $!";

               Examples:

                   $ARTICLE = 100;
                   open ARTICLE or die "Can't find article $ARTICLE: $!\n";
                   while (<ARTICLE>) {...

                   open(LOG, '>>/usr/spool/news/twitlog');     # (log is reserved)
                   # if the open fails, output is discarded

                   open(my $dbase, '+<', 'dbase.mine')         # open for update
                       or die "Can't open 'dbase.mine' for update: $!";

                   open(my $dbase, '+<dbase.mine')                     # ditto
                       or die "Can't open 'dbase.mine' for update: $!";

                   open(ARTICLE, '-|', "caesar <$article")     # decrypt article
                       or die "Can't start caesar: $!";

                   open(ARTICLE, "caesar <$article |")         # ditto
                       or die "Can't start caesar: $!";

                   open(EXTRACT, "|sort >Tmp$$")               # $$ is our process id
                       or die "Can't start sort: $!";

                   # in memory files
                   open(MEMORY,'>', \$var)
                       or die "Can't open memory file: $!";
                   print MEMORY "foo!\n";                      # output will end up in $var

                   # process argument list of files along with any includes

                   foreach $file (@ARGV) {
                       process($file, 'fh00');
                           if (/^#include "(.*)"/) {
                               process($1, $input);
                               next;
                           }
                           #...                # whatever
                       }
                   }

               See perliol for detailed info on PerlIO.

               You may also, in the Bourne shell tradition, specify an EXPR
               beginning with '>&', in which case the rest of the string is
               interpreted as the name of a filehandle (or file descriptor, if
               numeric) to be duped (as dup(2)) and opened.  You may use "&"
               after ">", ">>", "<", "+>", "+>>", and "+<".  The mode you
               specify should match the mode of the original filehandle.
               (Duping a filehandle does not take into account any existing
               contents of IO buffers.) If you use the 3-arg form then you can
               pass either a number, the name of a filehandle or the normal
               "reference to a glob".

               Here is a script that saves, redirects, and restores "STDOUT"
               and "STDERR" using various methods:

                   #!/usr/bin/perl
                   open my $oldout, ">&STDOUT"     or die "Can't dup STDOUT: $!";
                   open OLDERR,     ">&", \*STDERR or die "Can't dup STDERR: $!";

                   open STDOUT, '>', "foo.out" or die "Can't redirect STDOUT: $!";
                   open STDERR, ">&STDOUT"     or die "Can't dup STDOUT: $!";

                   select STDERR; $| = 1;      # make unbuffered
                   select STDOUT; $| = 1;      # make unbuffered

                   print STDOUT "stdout 1\n";  # this works for
                   print STDERR "stderr 1\n";  # subprocesses too

                   open STDOUT, ">&", $oldout or die "Can't dup \$oldout: $!";
                   open STDERR, ">&OLDERR"    or die "Can't dup OLDERR: $!";

                   print STDOUT "stdout 2\n";
                   print STDERR "stderr 2\n";

               If you specify '<&=X', where "X" is a file descriptor number or
               a filehandle, then Perl will do an equivalent of C's "fdopen"
               of that file descriptor (and not call dup(2)); this is more
               parsimonious of file descriptors.  For example:

                   # open for input, reusing the fileno of $fd
                   open(FILEHANDLE, "<&=$fd")

               or

                   open(FILEHANDLE, "<&=", $fd)

               descriptors, like for example locking using flock().  If you do
               just "open(A, '>&gt;&B')", the filehandle A will not have the same
               file descriptor as B, and therefore flock(A) will not flock(B),
               and vice versa.  But with "open(A, '>&gt;&=B')" the filehandles
               will share the same file descriptor.

               Note that if you are using Perls older than 5.8.0, Perl will be
               using the standard C libraries' fdopen() to implement the "="
               functionality.  On many UNIX systems fdopen() fails when file
               descriptors exceed a certain value, typically 255.  For Perls
               5.8.0 and later, PerlIO is most often the default.

               You can see whether Perl has been compiled with PerlIO or not
               by running "perl -V" and looking for "useperlio=" line.  If
               "useperlio" is "define", you have PerlIO, otherwise you don't.

               If you open a pipe on the command '-', i.e., either '|-' or
               '-|' with 2-arguments (or 1-argument) form of open(), then
               there is an implicit fork done, and the return value of open is
               the pid of the child within the parent process, and 0 within
               the child process.  (Use "defined($pid)" to determine whether
               the open was successful.)  The filehandle behaves normally for
               the parent, but i/o to that filehandle is piped from/to the
               STDOUT/STDIN of the child process.  In the child process the
               filehandle isn't opened--i/o happens from/to the new STDOUT or
               STDIN.  Typically this is used like the normal piped open when
               you want to exercise more control over just how the pipe
               command gets executed, such as when you are running setuid, and
               don't want to have to scan shell commands for metacharacters.
               The following triples are more or less equivalent:

                   open(FOO, "|tr '[a-z]' '[A-Z]'");
                   open(FOO, '|-', "tr '[a-z]' '[A-Z]'");
                   open(FOO, '|-') || exec 'tr', '[a-z]', '[A-Z]';
                   open(FOO, '|-', "tr", '[a-z]', '[A-Z]');

                   open(FOO, "cat -n '$file'|");
                   open(FOO, '-|', "cat -n '$file'");
                   open(FOO, '-|') || exec 'cat', '-n', $file;
                   open(FOO, '-|', "cat", '-n', $file);

               The last example in each block shows the pipe as "list form",
               which is not yet supported on all platforms.  A good rule of
               thumb is that if your platform has true "fork()" (in other
               words, if your platform is UNIX) you can use the list form.

               See "Safe Pipe Opens" in perlipc for more examples of this.

               Beginning with v5.6.0, Perl will attempt to flush all files
               opened for output before any operation that may do a fork, but
               this may not be supported on some platforms (see perlport).  To
               be safe, you may need to set $| ($AUTOFLUSH in English) or call
               the "autoflush()" method of "IO::Handle" on any open handles.

               user could specify a filename of "rsh cat file |", or you could
               change certain filenames as needed:

                   $filename =~ s/(.*\.gz)\s*$/gzip -dc < $1|/;
                   open(FH, $filename) or die "Can't open $filename: $!";

               Use 3-argument form to open a file with arbitrary weird
               characters in it,

                   open(FOO, '<', $file);

               otherwise it's necessary to protect any leading and trailing
               whitespace:

                   $file =~ s#^(\s)#./$1#;
                   open(FOO, "< $file\0");

               (this may not work on some bizarre filesystems).  One should
               conscientiously choose between the magic and 3-arguments form
               of open():

                   open IN, $ARGV[0];

               will allow the user to specify an argument of the form "rsh cat
               file |", but will not work on a filename which happens to have
               a trailing space, while

                   open IN, '<', $ARGV[0];

               will have exactly the opposite restrictions.

               If you want a "real" C "open" (see open(2) on your system),
               then you should use the "sysopen" function, which involves no
               such magic (but may use subtly different filemodes than Perl
               open(), which is mapped to C fopen()).  This is another way to
               protect your filenames from interpretation.  For example:

                   use IO::Handle;
                   sysopen(HANDLE, $path, O_RDWR|O_CREAT|O_EXCL)
                       or die "sysopen $path: $!";
                   $oldfh = select(HANDLE); $| = 1; select($oldfh);
                   print HANDLE "stuff $$\n";
                   seek(HANDLE, 0, 0);
                   print "File contains: ", <HANDLE>;

               Using the constructor from the "IO::Handle" package (or one of
               its subclasses, such as "IO::File" or "IO::Socket"), you can
               generate anonymous filehandles that have the scope of whatever
               variables hold references to them, and automatically close
               whenever and however you leave that scope:

                   use IO::File;
                   #...
                   sub read_myfile_munged {

       opendir DIRHANDLE,EXPR
               Opens a directory named EXPR for processing by "readdir",
               "telldir", "seekdir", "rewinddir", and "closedir".  Returns
               true if successful.  DIRHANDLE may be an expression whose value
               can be used as an indirect dirhandle, usually the real
               dirhandle name.  If DIRHANDLE is an undefined scalar variable
               (or array or hash element), the variable is assigned a
               reference to a new anonymous dirhandle.  DIRHANDLEs have their
               own namespace separate from FILEHANDLEs.

               See example at "readdir".

       ord EXPR
       ord     Returns the numeric (the native 8-bit encoding, like ASCII or
               EBCDIC, or Unicode) value of the first character of EXPR.  If
               EXPR is omitted, uses $_.

               For the reverse, see "chr".  See perlunicode for more about
               Unicode.

       our EXPR
       our TYPE EXPR
       our EXPR : ATTRS
       our TYPE EXPR : ATTRS
               "our" associates a simple name with a package variable in the
               current package for use within the current scope.  When "use
               strict 'vars'" is in effect, "our" lets you use declared global
               variables without qualifying them with package names, within
               the lexical scope of the "our" declaration.  In this way "our"
               differs from "use vars", which is package scoped.

               Unlike "my", which both allocates storage for a variable and
               associates a simple name with that storage for use within the
               current scope, "our" associates a simple name with a package
               variable in the current package, for use within the current
               scope.  In other words, "our" has the same scoping rules as
               "my", but does not necessarily create a variable.

               If more than one value is listed, the list must be placed in
               parentheses.

                   our $foo;
                   our($bar, $baz);

               An "our" declaration declares a global variable that will be
               visible across its entire lexical scope, even across package
               boundaries.  The package in which the variable is entered is
               determined at the point of the declaration, not at the point of
               use.  This means the following behavior holds:

                   package Foo;
                   our $bar;           # declares $Foo::bar for rest of lexical scope
                   $bar = 20;

                   package Foo;
                   our $bar;           # declares $Foo::bar for rest of lexical scope
                   $bar = 20;

                   package Bar;
                   our $bar = 30;      # declares $Bar::bar for rest of lexical scope
                   print $bar;         # prints 30

                   our $bar;           # emits warning but has no other effect
                   print $bar;         # still prints 30

               An "our" declaration may also have a list of attributes
               associated with it.

               The exact semantics and interface of TYPE and ATTRS are still
               evolving.  TYPE is currently bound to the use of "fields"
               pragma, and attributes are handled using the "attributes"
               pragma, or starting from Perl 5.8.0 also via the
               "Attribute::Handlers" module.  See "Private Variables via my()"
               in perlsub for details, and fields, attributes, and
               Attribute::Handlers.

       pack TEMPLATE,LIST
               Takes a LIST of values and converts it into a string using the
               rules given by the TEMPLATE.  The resulting string is the
               concatenation of the converted values.  Typically, each
               converted value looks like its machine-level representation.
               For example, on 32-bit machines an integer may be represented
               by a sequence of 4 bytes that will be converted to a sequence
               of 4 characters.

               The TEMPLATE is a sequence of characters that give the order
               and type of values, as follows:

                   a   A string with arbitrary binary data, will be null padded.
                   A   A text (ASCII) string, will be space padded.
                   Z   A null terminated (ASCIZ) string, will be null padded.

                   b   A bit string (ascending bit order inside each byte, like vec()).
                   B   A bit string (descending bit order inside each byte).
                   h   A hex string (low nybble first).
                   H   A hex string (high nybble first).

                   c   A signed char (8-bit) value.
                   C   An unsigned char (octet) value.
                   W   An unsigned char value (can be greater than 255).

                   s   A signed short (16-bit) value.
                   S   An unsigned short value.

                   l   A signed long (32-bit) value.
                   L   An unsigned long value.

                   q   A signed quad (64-bit) value.
                   v   An unsigned short (16-bit) in "VAX" (little-endian) order.
                   V   An unsigned long (32-bit) in "VAX" (little-endian) order.

                   j   A Perl internal signed integer value (IV).
                   J   A Perl internal unsigned integer value (UV).

                   f   A single-precision float in the native format.
                   d   A double-precision float in the native format.

                   F   A Perl internal floating point value (NV) in the native format
                   D   A long double-precision float in the native format.
                         (Long doubles are available only if your system supports long
                          double values _and_ if Perl has been compiled to support those.
                          Causes a fatal error otherwise.)

                   p   A pointer to a null-terminated string.
                   P   A pointer to a structure (fixed-length string).

                   u   A uuencoded string.
                   U   A Unicode character number.  Encodes to a character in character mode
                       and UTF-8 (or UTF-EBCDIC in EBCDIC platforms) in byte mode.

                   w   A BER compressed integer (not an ASN.1 BER, see perlpacktut for
                       details).  Its bytes represent an unsigned integer in base 128,
                       most significant digit first, with as few digits as possible.  Bit
                       eight (the high bit) is set on each byte except the last.

                   x   A null byte.
                   X   Back up a byte.
                   @   Null fill or truncate to absolute position, counted from the
                       start of the innermost ()-group.
                   .   Null fill or truncate to absolute position specified by value.
                   (   Start of a ()-group.

               One or more of the modifiers below may optionally follow some
               letters in the TEMPLATE (the second column lists the letters
               for which the modifier is valid):

                   !   sSlLiI     Forces native (short, long, int) sizes instead
                                  of fixed (16-/32-bit) sizes.

                       xX         Make x and X act as alignment commands.

                       nNvV       Treat integers as signed instead of unsigned.

                       @.         Specify position as byte offset in the internal
                                  representation of the packed string. Efficient but
                                  dangerous.

                   >   sSiIlLqQ   Force big-endian byte-order on the type.
                       jJfFdDpP   (The "big end" touches the construct.)

                   <   sSiIlLqQ   Force little-endian byte-order on the type.
                       jJfFdDpP   (The "little end" touches the construct.)
                       many items are left, except for "@", "x", "X", where it
                       is equivalent to 0, for <.> where it means relative to
                       string start and "u", where it is equivalent to 1 (or
                       45, which is the same).  A numeric repeat count may
                       optionally be enclosed in brackets, as in "pack
                       'C[80]', @arr".

                       One can replace the numeric repeat count by a template
                       enclosed in brackets; then the packed length of this
                       template in bytes is used as a count.  For example,
                       "x[L]" skips a long (it skips the number of bytes in a
                       long); the template "$t X[$t] $t" unpack()s twice what
                       $t unpacks.  If the template in brackets contains
                       alignment commands (such as "x![d]"), its packed length
                       is calculated as if the start of the template has the
                       maximal possible alignment.

                       When used with "Z", "*" results in the addition of a
                       trailing null byte (so the packed result will be one
                       longer than the byte "length" of the item).

                       When used with "@", the repeat count represents an
                       offset from the start of the innermost () group.

                       When used with ".", the repeat count is used to
                       determine the starting position from where the value
                       offset is calculated. If the repeat count is 0, it's
                       relative to the current position. If the repeat count
                       is "*", the offset is relative to the start of the
                       packed string. And if its an integer "n" the offset is
                       relative to the start of the n-th innermost () group
                       (or the start of the string if "n" is bigger then the
                       group level).

                       The repeat count for "u" is interpreted as the maximal
                       number of bytes to encode per line of output, with 0, 1
                       and 2 replaced by 45. The repeat count should not be
                       more than 65.

               o       The "a", "A", and "Z" types gobble just one value, but
                       pack it as a string of length count, padding with nulls
                       or spaces as necessary.  When unpacking, "A" strips
                       trailing whitespace and nulls, "Z" strips everything
                       after the first null, and "a" returns data verbatim.

                       If the value-to-pack is too long, it is truncated.  If
                       too long and an explicit count is provided, "Z" packs
                       only "$count-1" bytes, followed by a null byte.  Thus
                       "Z" always packs a trailing null (except when the count
                       is 0).

               o       Likewise, the "b" and "B" fields pack a string that
                       many bits long.  Each character of the input field of
                       pack() generates 1 bit of the result.  Each result bit
                       If the length of the input string is not exactly
                       divisible by 8, the remainder is packed as if the input
                       string were padded by null characters at the end.
                       Similarly, during unpack()ing the "extra" bits are
                       ignored.

                       If the input string of pack() is longer than needed,
                       extra characters are ignored. A "*" for the repeat
                       count of pack() means to use all the characters of the
                       input field.  On unpack()ing the bits are converted to
                       a string of "0"s and "1"s.

               o       The "h" and "H" fields pack a string that many nybbles
                       (4-bit groups, representable as hexadecimal digits,
                       0-9a-f) long.

                       Each character of the input field of pack() generates 4
                       bits of the result.  For non-alphabetical characters
                       the result is based on the 4 least-significant bits of
                       the input character, i.e., on "ord($char)%16".  In
                       particular, characters "0" and "1" generate nybbles 0
                       and 1, as do bytes "\0" and "\1".  For characters
                       "a".."f" and "A".."F" the result is compatible with the
                       usual hexadecimal digits, so that "a" and "A" both
                       generate the nybble "0xa==10".  The result for
                       characters "g".."z" and "G".."Z" is not well-defined.

                       Starting from the beginning of the input string of
                       pack(), each pair of characters is converted to 1
                       character of output.  With format "h" the first
                       character of the pair determines the least-significant
                       nybble of the output character, and with format "H" it
                       determines the most-significant nybble.

                       If the length of the input string is not even, it
                       behaves as if padded by a null character at the end.
                       Similarly, during unpack()ing the "extra" nybbles are
                       ignored.

                       If the input string of pack() is longer than needed,
                       extra characters are ignored.  A "*" for the repeat
                       count of pack() means to use all the characters of the
                       input field.  On unpack()ing the nybbles are converted
                       to a string of hexadecimal digits.

               o       The "p" type packs a pointer to a null-terminated
                       string.  You are responsible for ensuring the string is
                       not a temporary value (which can potentially get
                       deallocated before you get around to using the packed
                       result).  The "P" type packs a pointer to a structure
                       of the size indicated by the length.  A NULL pointer is
                       created if the corresponding value for "p" or "P" is
                       "undef", similarly for unpack().

                       the length-item describes how the length value is
                       packed. The ones likely to be of most use are integer-
                       packing ones like "n" (for Java strings), "w" (for
                       ASN.1 or SNMP) and "N" (for Sun XDR).

                       For "pack", the sequence-item may have a repeat count,
                       in which case the minimum of that and the number of
                       available items is used as argument for the length-
                       item. If it has no repeat count or uses a '*', the
                       number of available items is used.

                       For "unpack" an internal stack of integer arguments
                       unpacked so far is used. You write "/"sequence-item and
                       the repeat count is obtained by popping off the last
                       element from the stack. The sequence-item must not have
                       a repeat count.

                       If the sequence-item refers to a string type ("A", "a"
                       or "Z"), the length-item is a string length, not a
                       number of strings. If there is an explicit repeat count
                       for pack, the packed string will be adjusted to that
                       given length.

                           unpack 'W/a', "\04Gurusamy";            gives ('Guru')
                           unpack 'a3/A A*', '007 Bond  J ';       gives (' Bond', 'J')
                           unpack 'a3 x2 /A A*', '007: Bond, J.';  gives ('Bond, J', '.')
                           pack 'n/a* w/a','hello,','world';       gives "\000\006hello,\005world"
                           pack 'a/W2', ord('a') .. ord('z');      gives '2ab'

                       The length-item is not returned explicitly from
                       "unpack".

                       Adding a count to the length-item letter is unlikely to
                       do anything useful, unless that letter is "A", "a" or
                       "Z".  Packing with a length-item of "a" or "Z" may
                       introduce "\000" characters, which Perl does not regard
                       as legal in numeric strings.

               o       The integer types "s", "S", "l", and "L" may be
                       followed by a "!" modifier to signify native shorts or
                       longs--as you can see from above for example a bare "l"
                       does mean exactly 32 bits, the native "long" (as seen
                       by the local C compiler) may be larger.  This is an
                       issue mainly in 64-bit platforms.  You can see whether
                       using "!" makes any difference by

                               print length(pack("s")), " ", length(pack("s!")), "\n";
                               print length(pack("l")), " ", length(pack("l!")), "\n";

                       "i!" and "I!" also work but only because of
                       completeness; they are identical to "i" and "I".

                       The actual sizes (in bytes) of native shorts, ints,
                       longs, and long longs on the platform where Perl was
                       and "J" are inherently non-portable between processors
                       and operating systems because they obey the native
                       byteorder and endianness.  For example a 4-byte integer
                       0x12345678 (305419896 decimal) would be ordered
                       natively (arranged in and handled by the CPU registers)
                       into bytes as

                               0x12 0x34 0x56 0x78     # big-endian
                               0x78 0x56 0x34 0x12     # little-endian

                       Basically, the Intel and VAX CPUs are little-endian,
                       while everybody else, for example Motorola m68k/88k,
                       PPC, Sparc, HP PA, Power, and Cray are big-endian.
                       Alpha and MIPS can be either: Digital/Compaq used/uses
                       them in little-endian mode; SGI/Cray uses them in big-
                       endian mode.

                       The names `big-endian' and `little-endian' are comic
                       references to the classic "Gulliver's Travels" (via the
                       paper "On Holy Wars and a Plea for Peace" by Danny
                       Cohen, USC/ISI IEN 137, April 1, 1980) and the egg-
                       eating habits of the Lilliputians.

                       Some systems may have even weirder byte orders such as

                               0x56 0x78 0x12 0x34
                               0x34 0x12 0x78 0x56

                       You can see your system's preference with

                               print join(" ", map { sprintf "%#02x", $_ }
                                                   unpack("W*",pack("L",0x12345678))), "\n";

                       The byteorder on the platform where Perl was built is
                       also available via Config:

                               use Config;
                               print $Config{byteorder}, "\n";

                       Byteorders '1234' and '12345678' are little-endian,
                       '4321' and '87654321' are big-endian.

                       If you want portable packed integers you can either use
                       the formats "n", "N", "v", and "V", or you can use the
                       ">" and "<" modifiers.  These modifiers are only
                       available as of perl 5.9.2.  See also perlport.

               o       All integer and floating point formats as well as "p"
                       and "P" and "()"-groups may be followed by the ">" or
                       "<" modifiers to force big- or little- endian byte-
                       order, respectively.  This is especially useful, since
                       "n", "N", "v" and "V" don't cover signed integers,
                       64-bit integers and floating point values.  However,
                       there are some things to keep in mind.
                       point values for data exchange can only work if all
                       platforms are using the same binary representation
                       (e.g. IEEE floating point format).  Even if all
                       platforms are using IEEE, there may be subtle
                       differences.  Being able to use ">" or "<" on floating
                       point values can be very useful, but also very
                       dangerous if you don't know exactly what you're doing.
                       It is definitely not a general way to portably store
                       floating point values.

                       When using ">" or "<" on an "()"-group, this will
                       affect all types inside the group that accept the byte-
                       order modifiers, including all subgroups.  It will
                       silently be ignored for all other types.  You are not
                       allowed to override the byte-order within a group that
                       already has a byte-order modifier suffix.

               o       Real numbers (floats and doubles) are in the native
                       machine format only; due to the multiplicity of
                       floating formats around, and the lack of a standard
                       "network" representation, no facility for interchange
                       has been made.  This means that packed floating point
                       data written on one machine may not be readable on
                       another - even if both use IEEE floating point
                       arithmetic (as the endian-ness of the memory
                       representation is not part of the IEEE spec).  See also
                       perlport.

                       If you know exactly what you're doing, you can use the
                       ">" or "<" modifiers to force big- or little-endian
                       byte-order on floating point values.

                       Note that Perl uses doubles (or long doubles, if
                       configured) internally for all numeric calculation, and
                       converting from double into float and thence back to
                       double again will lose precision (i.e., "unpack("f",
                       pack("f", $foo)") will not in general equal $foo).

               o       Pack and unpack can operate in two modes, character
                       mode ("C0" mode) where the packed string is processed
                       per character and UTF-8 mode ("U0" mode) where the
                       packed string is processed in its UTF-8-encoded Unicode
                       form on a byte by byte basis. Character mode is the
                       default unless the format string starts with an "U".
                       You can switch mode at any moment with an explicit "C0"
                       or "U0" in the format. A mode is in effect until the
                       next mode switch or until the end of the ()-group in
                       which it was entered.

               o       You must yourself do any alignment or padding by
                       inserting for example enough 'x'es while packing.
                       There is no way to pack() and unpack() could know where
                       the characters are going to or coming from.  Therefore
                       "pack" (and "unpack") handle their output and input as

               o       "x" and "X" accept "!" modifier.  In this case they act
                       as alignment commands: they jump forward/back to the
                       closest position aligned at a multiple of "count"
                       characters. For example, to pack() or unpack() C's
                       "struct {char c; double d; char cc[2]}" one may need to
                       use the template "W x![d] d W[2]"; this assumes that
                       doubles must be aligned on the double's size.

                       For alignment commands "count" of 0 is equivalent to
                       "count" of 1; both result in no-ops.

               o       "n", "N", "v" and "V" accept the "!" modifier. In this
                       case they will represent signed 16-/32-bit integers in
                       big-/little-endian order.  This is only portable if all
                       platforms sharing the packed data use the same binary
                       representation for signed integers (e.g. all platforms
                       are using two's complement representation).

               o       A comment in a TEMPLATE starts with "#" and goes to the
                       end of line.  White space may be used to separate pack
                       codes from each other, but modifiers and a repeat count
                       must follow immediately.

               o       If TEMPLATE requires more arguments to pack() than
                       actually given, pack() assumes additional "" arguments.
                       If TEMPLATE requires fewer arguments to pack() than
                       actually given, extra arguments are ignored.

               Examples:

                   $foo = pack("WWWW",65,66,67,68);
                   # foo eq "ABCD"
                   $foo = pack("W4",65,66,67,68);
                   # same thing
                   $foo = pack("W4",0x24b6,0x24b7,0x24b8,0x24b9);
                   # same thing with Unicode circled letters.
                   $foo = pack("U4",0x24b6,0x24b7,0x24b8,0x24b9);
                   # same thing with Unicode circled letters. You don't get the UTF-8
                   # bytes because the U at the start of the format caused a switch to
                   # U0-mode, so the UTF-8 bytes get joined into characters
                   $foo = pack("C0U4",0x24b6,0x24b7,0x24b8,0x24b9);
                   # foo eq "\xe2\x92\xb6\xe2\x92\xb7\xe2\x92\xb8\xe2\x92\xb9"
                   # This is the UTF-8 encoding of the string in the previous example

                   $foo = pack("ccxxcc",65,66,67,68);
                   # foo eq "AB\0\0CD"

                   # note: the above examples featuring "W" and "c" are true
                   # only on ASCII and ASCII-derived systems such as ISO Latin 1
                   # and UTF-8.  In EBCDIC the first example would be
                   # $foo = pack("WWWW",193,194,195,196);

                   $foo = pack("s2",1,2);
                   # "\1\0\2\0" on little-endian
                   # a real struct tm (on my system anyway)

                   $utmp_template = "Z8 Z8 Z16 L";
                   $utmp = pack($utmp_template, @utmp1);
                   # a struct utmp (BSDish)

                   @utmp2 = unpack($utmp_template, $utmp);
                   # "@utmp1" eq "@utmp2"

                   sub bintodec {
                       unpack("N", pack("B32", substr("0" x 32 . shift, -32)));
                   }

                   $foo = pack('sx2l', 12, 34);
                   # short 12, two zero bytes padding, long 34
                   $bar = pack('s@4l', 12, 34);
                   # short 12, zero fill to position 4, long 34
                   # $foo eq $bar
                   $baz = pack('s.l', 12, 4, 34);
                   # short 12, zero fill to position 4, long 34

                   $foo = pack('nN', 42, 4711);
                   # pack big-endian 16- and 32-bit unsigned integers
                   $foo = pack('S>L>', 42, 4711);
                   # exactly the same
                   $foo = pack('s<l<', -42, 4711);
                   # pack little-endian 16- and 32-bit signed integers
                   $foo = pack('(sl)<', -42, 4711);
                   # exactly the same

               The same template may generally also be used in unpack().

       package NAMESPACE
       package Declares the compilation unit as being in the given namespace.
               The scope of the package declaration is from the declaration
               itself through the end of the enclosing block, file, or eval
               (the same as the "my" operator).  All further unqualified
               dynamic identifiers will be in this namespace.  A package
               statement affects only dynamic variables--including those
               you've used "local" on--but not lexical variables, which are
               created with "my".  Typically it would be the first declaration
               in a file to be included by the "require" or "use" operator.
               You can switch into a package in more than one place; it merely
               influences which symbol table is used by the compiler for the
               rest of that block.  You can refer to variables and filehandles
               in other packages by prefixing the identifier with the package
               name and a double colon:  $Package::Variable.  If the package
               name is null, the "main" package as assumed.  That is, $::sail
               is equivalent to $main::sail (as well as to "$main'sail", still
               seen in older code).

               See "Packages" in perlmod for more information about packages,
               modules, and classes.  See perlsub for other scoping issues.

               will be set for the newly opened file descriptors as determined
               by the value of $^F.  See "$^F" in perlvar.

       pop ARRAY
       pop     Pops and returns the last value of the array, shortening the
               array by one element.

               If there are no elements in the array, returns the undefined
               value (although this may happen at other times as well).  If
               ARRAY is omitted, pops the @ARGV array in the main program, and
               the @_ array in subroutines, just like "shift".

       pos SCALAR
       pos     Returns the offset of where the last "m//g" search left off for
               the variable in question ($_ is used when the variable is not
               specified).  Note that 0 is a valid match offset.  "undef"
               indicates that the search position is reset (usually due to
               match failure, but can also be because no match has yet been
               performed on the scalar). "pos" directly accesses the location
               used by the regexp engine to store the offset, so assigning to
               "pos" will change that offset, and so will also influence the
               "\G" zero-width assertion in regular expressions. Because a
               failed "m//gc" match doesn't reset the offset, the return from
               "pos" won't change either in this case.  See perlre and perlop.

       print FILEHANDLE LIST
       print LIST
       print   Prints a string or a list of strings.  Returns true if
               successful.  FILEHANDLE may be a scalar variable name, in which
               case the variable contains the name of or a reference to the
               filehandle, thus introducing one level of indirection.  (NOTE:
               If FILEHANDLE is a variable and the next token is a term, it
               may be misinterpreted as an operator unless you interpose a "+"
               or put parentheses around the arguments.)  If FILEHANDLE is
               omitted, prints by default to standard output (or to the last
               selected output channel--see "select").  If LIST is also
               omitted, prints $_ to the currently selected output channel.
               To set the default output channel to something other than
               STDOUT use the select operation.  The current value of $, (if
               any) is printed between each LIST item.  The current value of
               "$\" (if any) is printed after the entire LIST has been
               printed.  Because print takes a LIST, anything in the LIST is
               evaluated in list context, and any subroutine that you call
               will have one or more of its expressions evaluated in list
               context.  Also be careful not to follow the print keyword with
               a left parenthesis unless you want the corresponding right
               parenthesis to terminate the arguments to the print--interpose
               a "+" or put parentheses around all the arguments.

               Note that if you're storing FILEHANDLEs in an array, or if
               you're using any other expression more complex than a scalar
               variable to retrieve it, you will have to use a block returning
               the filehandle value instead:

               LC_NUMERIC locale.  See perllocale and POSIX.

               Don't fall into the trap of using a "printf" when a simple
               "print" would do.  The "print" is more efficient and less error
               prone.

       prototype FUNCTION
               Returns the prototype of a function as a string (or "undef" if
               the function has no prototype).  FUNCTION is a reference to, or
               the name of, the function whose prototype you want to retrieve.

               If FUNCTION is a string starting with "CORE::", the rest is
               taken as a name for Perl builtin.  If the builtin is not
               overridable (such as "qw//") or if its arguments cannot be
               adequately expressed by a prototype (such as "system"),
               prototype() returns "undef", because the builtin does not
               really behave like a Perl function.  Otherwise, the string
               describing the equivalent prototype is returned.

       push ARRAY,LIST
               Treats ARRAY as a stack, and pushes the values of LIST onto the
               end of ARRAY.  The length of ARRAY increases by the length of
               LIST.  Has the same effect as

                   for $value (LIST) {
                       $ARRAY[++$#ARRAY] = $value;
                   }

               but is more efficient.  Returns the number of elements in the
               array following the completed "push".

       q/STRING/
       qq/STRING/
       qx/STRING/
       qw/STRING/
               Generalized quotes.  See "Quote-Like Operators" in perlop.

       qr/STRING/
               Regexp-like quote.  See "Regexp Quote-Like Operators" in
               perlop.

       quotemeta EXPR
       quotemeta
               Returns the value of EXPR with all non-"word" characters
               backslashed.  (That is, all characters not matching
               "/[A-Za-z_0-9]/" will be preceded by a backslash in the
               returned string, regardless of any locale settings.)  This is
               the internal function implementing the "\Q" escape in double-
               quoted strings.

               If EXPR is omitted, uses $_.

       rand EXPR
       rand    Returns a random fractional number greater than or equal to 0

               returns a random integer between 0 and 9, inclusive.

               (Note: If your rand function consistently returns numbers that
               are too large or too small, then your version of Perl was
               probably compiled with the wrong number of RANDBITS.)

       read FILEHANDLE,SCALAR,LENGTH,OFFSET
       read FILEHANDLE,SCALAR,LENGTH
               Attempts to read LENGTH characters of data into variable SCALAR
               from the specified FILEHANDLE.  Returns the number of
               characters actually read, 0 at end of file, or undef if there
               was an error (in the latter case $! is also set).  SCALAR will
               be grown or shrunk so that the last character actually read is
               the last character of the scalar after the read.

               An OFFSET may be specified to place the read data at some place
               in the string other than the beginning.  A negative OFFSET
               specifies placement at that many characters counting backwards
               from the end of the string.  A positive OFFSET greater than the
               length of SCALAR results in the string being padded to the
               required size with "\0" bytes before the result of the read is
               appended.

               The call is actually implemented in terms of either Perl's or
               system's fread() call.  To get a true read(2) system call, see
               "sysread".

               Note the characters: depending on the status of the filehandle,
               either (8-bit) bytes or characters are read.  By default all
               filehandles operate on bytes, but for example if the filehandle
               has been opened with the ":utf8" I/O layer (see "open", and the
               "open" pragma, open), the I/O will operate on UTF-8 encoded
               Unicode characters, not bytes.  Similarly for the ":encoding"
               pragma: in that case pretty much any characters can be read.

       readdir DIRHANDLE
               Returns the next directory entry for a directory opened by
               "opendir".  If used in list context, returns all the rest of
               the entries in the directory.  If there are no more entries,
               returns an undefined value in scalar context or a null list in
               list context.

               If you're planning to filetest the return values out of a
               "readdir", you'd better prepend the directory in question.
               Otherwise, because we didn't "chdir" there, it would have been
               testing the wrong file.

                   opendir(my $dh, $some_dir) || die "can't opendir $some_dir: $!";
                   @dots = grep { /^\./ && -f "$some_dir/$_" } readdir($dh);
                   closedir $dh;

       readline EXPR
       readline

               This is the internal function implementing the "<EXPR>"
               operator, but you can use it directly.  The "<EXPR>" operator
               is discussed in more detail in "I/O Operators" in perlop.

                   $line = <STDIN>;
                   $line = readline(*STDIN);           # same thing

               If readline encounters an operating system error, $! will be
               set with the corresponding error message.  It can be helpful to
               check $! when you are reading from filehandles you don't trust,
               such as a tty or a socket.  The following example uses the
               operator form of "readline", and takes the necessary steps to
               ensure that "readline" was successful.

                   for (;;) {
                       undef $!;
                       unless (defined( $line = <> )) {
                           last if eof;
                           die $! if $!;
                       }
                       # ...
                   }

       readlink EXPR
       readlink
               Returns the value of a symbolic link, if symbolic links are
               implemented.  If not, gives a fatal error.  If there is some
               system error, returns the undefined value and sets $! (errno).
               If EXPR is omitted, uses $_.

       readpipe EXPR
       readpipe
               EXPR is executed as a system command.  The collected standard
               output of the command is returned.  In scalar context, it comes
               back as a single (potentially multi-line) string.  In list
               context, returns a list of lines (however you've defined lines
               with $/ or $INPUT_RECORD_SEPARATOR).  This is the internal
               function implementing the "qx/EXPR/" operator, but you can use
               it directly.  The "qx/EXPR/" operator is discussed in more
               detail in "I/O Operators" in perlop.  If EXPR is omitted, uses
               $_.

       recv SOCKET,SCALAR,LENGTH,FLAGS
               Receives a message on a socket.  Attempts to receive LENGTH
               characters of data into variable SCALAR from the specified
               SOCKET filehandle.  SCALAR will be grown or shrunk to the
               length actually read.  Takes the same flags as the system call
               of the same name.  Returns the address of the sender if
               SOCKET's protocol supports this; returns an empty string
               otherwise.  If there's an error, returns the undefined value.
               This call is actually implemented in terms of recvfrom(2)
               system call.  See "UDP: Message Passing" in perlipc for
               examples.
               the conditional again.  The "continue" block, if any, is not
               executed.  If the LABEL is omitted, the command refers to the
               innermost enclosing loop.  Programs that want to lie to
               themselves about what was just input normally use this command:

                   # a simpleminded Pascal comment stripper
                   # (warning: assumes no { or } in strings)
                   LINE: while (<STDIN>) {
                       while (s|({.*}.*){.*}|$1 |) {}
                       s|{.*}| |;
                       if (s|{.*| |) {
                           $front = $_;
                           while (<STDIN>) {
                               if (/}/) {      # end of comment?
                                   s|^|$front\{|;
                                   redo LINE;
                               }
                           }
                       }
                       print;
                   }

               "redo" cannot be used to retry a block which returns a value
               such as "eval {}", "sub {}" or "do {}", and should not be used
               to exit a grep() or map() operation.

               Note that a block by itself is semantically identical to a loop
               that executes once.  Thus "redo" inside such a block will
               effectively turn it into a looping construct.

               See also "continue" for an illustration of how "last", "next",
               and "redo" work.

       ref EXPR
       ref     Returns a non-empty string if EXPR is a reference, the empty
               string otherwise. If EXPR is not specified, $_ will be used.
               The value returned depends on the type of thing the reference
               is a reference to.  Builtin types include:

                   SCALAR
                   ARRAY
                   HASH
                   CODE
                   REF
                   GLOB
                   LVALUE
                   FORMAT
                   IO
                   VSTRING
                   Regexp

               If the referenced object has been blessed into a package, then
               that package name is returned instead.  You can think of "ref"
               as a "typeof" operator.

               The result "Regexp" indicates that the argument is a regular
               expression resulting from "qr//".

               See also perlref.

       rename OLDNAME,NEWNAME
               Changes the name of a file; an existing file NEWNAME will be
               clobbered.  Returns true for success, false otherwise.

               Behavior of this function varies wildly depending on your
               system implementation.  For example, it will usually not work
               across file system boundaries, even though the system mv
               command sometimes compensates for this.  Other restrictions
               include whether it works on directories, open files, or pre-
               existing files.  Check perlport and either the rename(2)
               manpage or equivalent system documentation for details.

               For a platform independent "move" function look at the
               File::Copy module.

       require VERSION
       require EXPR
       require Demands a version of Perl specified by VERSION, or demands some
               semantics specified by EXPR or by $_ if EXPR is not supplied.

               VERSION may be either a numeric argument such as 5.006, which
               will be compared to $], or a literal of the form v5.6.1, which
               will be compared to $^V (aka $PERL_VERSION).  A fatal error is
               produced at run time if VERSION is greater than the version of
               the current Perl interpreter.  Compare with "use", which can do
               a similar check at compile time.

               Specifying VERSION as a literal of the form v5.6.1 should
               generally be avoided, because it leads to misleading error
               messages under earlier versions of Perl that do not support
               this syntax.  The equivalent numeric version should be used
               instead.

                   require v5.6.1;     # run time version check
                   require 5.6.1;      # ditto
                   require 5.006_001;  # ditto; preferred for backwards compatibility

               Otherwise, "require" demands that a library file be included if
               it hasn't already been included.  The file is included via the
               do-FILE mechanism, which is essentially just a variety of
               "eval" with the caveat that lexical variables in the invoking
               script will be invisible to the included code.  Has semantics
               similar to the following subroutine:

                   sub require {
                      my ($filename) = @_;
                      if (exists $INC{$filename}) {
                          return 1 if $INC{$filename};
                          die "Can't find $filename in \@INC";
                      }
                      if ($@) {
                          $INC{$filename} = undef;
                          die $@;
                      } elsif (!$result) {
                          delete $INC{$filename};
                          die "$filename did not return true value";
                      } else {
                          return $result;
                      }
                   }

               Note that the file will not be included twice under the same
               specified name.

               The file must return true as the last statement to indicate
               successful execution of any initialization code, so it's
               customary to end such a file with "1;" unless you're sure it'll
               return true otherwise.  But it's better just to put the "1;",
               in case you add more statements.

               If EXPR is a bareword, the require assumes a ".pm" extension
               and replaces "::" with "/" in the filename for you, to make it
               easy to load standard modules.  This form of loading of modules
               does not risk altering your namespace.

               In other words, if you try this:

                       require Foo::Bar;    # a splendid bareword

               The require function will actually look for the "Foo/Bar.pm"
               file in the directories specified in the @INC array.

               But if you try this:

                       $class = 'Foo::Bar';
                       require $class;      # $class is not a bareword
                   #or
                       require "Foo::Bar";  # not a bareword because of the ""

               The require function will look for the "Foo::Bar" file in the
               @INC array and will complain about not finding "Foo::Bar"
               there.  In this case you can do:

                       eval "require $class";

               Now that you understand how "require" looks for files in the
               case of a bareword argument, there is a little extra
               functionality going on behind the scenes.  Before "require"
               looks for a ".pm" extension, it will first look for a similar
               filename with a ".pmc" extension. If this file is found, it
               will be loaded in place of any file ending in a ".pm"
               extension.
               following order:

               1.  A filehandle, from which the file will be read.

               2.  A reference to a subroutine. If there is no filehandle
                   (previous item), then this subroutine is expected to
                   generate one line of source code per call, writing the line
                   into $_ and returning 1, then returning 0 at "end of file".
                   If there is a filehandle, then the subroutine will be
                   called to act as a simple source filter, with the line as
                   read in $_.  Again, return 1 for each valid line, and 0
                   after all lines have been returned.

               3.  Optional state for the subroutine. The state is passed in
                   as $_[1]. A reference to the subroutine itself is passed in
                   as $_[0].

               If an empty list, "undef", or nothing that matches the first 3
               values above is returned then "require" will look at the
               remaining elements of @INC.  Note that this file handle must be
               a real file handle (strictly a typeglob, or reference to a
               typeglob, blessed or unblessed) - tied file handles will be
               ignored and return value processing will stop there.

               If the hook is an array reference, its first element must be a
               subroutine reference.  This subroutine is called as above, but
               the first parameter is the array reference.  This enables to
               pass indirectly some arguments to the subroutine.

               In other words, you can write:

                   push @INC, \&my_sub;
                   sub my_sub {
                       my ($coderef, $filename) = @_;  # $coderef is \&my_sub
                       ...
                   }

               or:

                   push @INC, [ \&my_sub, $x, $y, ... ];
                   sub my_sub {
                       my ($arrayref, $filename) = @_;
                       # Retrieve $x, $y, ...
                       my @parameters = @$arrayref[1..$#$arrayref];
                       ...
                   }

               If the hook is an object, it must provide an INC method that
               will be called as above, the first parameter being the object
               itself.  (Note that you must fully qualify the sub's name, as
               unqualified "INC" is always forced into package "main".)  Here
               is a typical code layout:

                   # In Foo.pm

               perlvar.

               For a yet-more-powerful import facility, see "use" and perlmod.

       reset EXPR
       reset   Generally used in a "continue" block at the end of a loop to
               clear variables and reset "??" searches so that they work
               again.  The expression is interpreted as a list of single
               characters (hyphens allowed for ranges).  All variables and
               arrays beginning with one of those letters are reset to their
               pristine state.  If the expression is omitted, one-match
               searches ("?pattern?") are reset to match again.  Resets only
               variables or searches in the current package.  Always returns
               1.  Examples:

                   reset 'X';          # reset all X variables
                   reset 'a-z';        # reset lower case variables
                   reset;              # just reset ?one-time? searches

               Resetting "A-Z" is not recommended because you'll wipe out your
               @ARGV and @INC arrays and your %ENV hash.  Resets only package
               variables--lexical variables are unaffected, but they clean
               themselves up on scope exit anyway, so you'll probably want to
               use them instead.  See "my".

       return EXPR
       return  Returns from a subroutine, "eval", or "do FILE" with the value
               given in EXPR.  Evaluation of EXPR may be in list, scalar, or
               void context, depending on how the return value will be used,
               and the context may vary from one execution to the next (see
               "wantarray").  If no EXPR is given, returns an empty list in
               list context, the undefined value in scalar context, and (of
               course) nothing at all in a void context.

               (Note that in the absence of an explicit "return", a
               subroutine, eval, or do FILE will automatically return the
               value of the last expression evaluated.)

       reverse LIST
               In list context, returns a list value consisting of the
               elements of LIST in the opposite order.  In scalar context,
               concatenates the elements of LIST and returns a string value
               with all characters in the opposite order.

                   print join(", ", reverse "world", "Hello"); # Hello, world

                   print scalar reverse "dlrow ,", "olleH";    # Hello, world

               Used without arguments in scalar context, reverse() reverses
               $_.

                   $_ = "dlrow ,olleH";
                   print reverse;                              # No output, list context
                   print scalar reverse;                       # Hello, world

               the "readdir" routine on DIRHANDLE.

       rindex STR,SUBSTR,POSITION
       rindex STR,SUBSTR
               Works just like index() except that it returns the position of
               the last occurrence of SUBSTR in STR.  If POSITION is
               specified, returns the last occurrence beginning at or before
               that position.

       rmdir FILENAME
       rmdir   Deletes the directory specified by FILENAME if that directory
               is empty.  If it succeeds it returns true, otherwise it returns
               false and sets $! (errno).  If FILENAME is omitted, uses $_.

               To remove a directory tree recursively ("rm -rf" on unix) look
               at the "rmtree" function of the File::Path module.

       s///    The substitution operator.  See "Regexp Quote-Like Operators"
               in perlop.

       say FILEHANDLE LIST
       say LIST
       say     Just like "print", but implicitly appends a newline.  "say
               LIST" is simply an abbreviation for "{ local $\ = "\n"; print
               LIST }".

               This keyword is only available when the "say" feature is
               enabled: see feature.

       scalar EXPR
               Forces EXPR to be interpreted in scalar context and returns the
               value of EXPR.

                   @counts = ( scalar @a, scalar @b, scalar @c );

               There is no equivalent operator to force an expression to be
               interpolated in list context because in practice, this is never
               needed.  If you really wanted to do so, however, you could use
               the construction "@{[ (some expression) ]}", but usually a
               simple "(some expression)" suffices.

               Because "scalar" is unary operator, if you accidentally use for
               EXPR a parenthesized list, this behaves as a scalar comma
               expression, evaluating all but the last element in void context
               and returning the final element evaluated in scalar context.
               This is seldom what you want.

               The following single statement:

                       print uc(scalar(&foo,$bar)),$baz;

               is the moral equivalent of these two:

                       &foo;

               "SEEK_SET", "SEEK_CUR", and "SEEK_END" (start of the file,
               current position, end of the file) from the Fcntl module.
               Returns 1 upon success, 0 otherwise.

               Note the in bytes: even if the filehandle has been set to
               operate on characters (for example by using the
               ":encoding(utf8)" open layer), tell() will return byte offsets,
               not character offsets (because implementing that would render
               seek() and tell() rather slow).

               If you want to position file for "sysread" or "syswrite", don't
               use "seek"--buffering makes its effect on the file's system
               position unpredictable and non-portable.  Use "sysseek"
               instead.

               Due to the rules and rigors of ANSI C, on some systems you have
               to do a seek whenever you switch between reading and writing.
               Amongst other things, this may have the effect of calling
               stdio's clearerr(3).  A WHENCE of 1 ("SEEK_CUR") is useful for
               not moving the file position:

                   seek(TEST,0,1);

               This is also useful for applications emulating "tail -f".  Once
               you hit EOF on your read, and then sleep for a while, you might
               have to stick in a seek() to reset things.  The "seek" doesn't
               change the current position, but it does clear the end-of-file
               condition on the handle, so that the next "<FILE>" makes Perl
               try again to read something.  We hope.

               If that doesn't work (some IO implementations are particularly
               cantankerous), then you may need something more like this:

                   for (;;) {
                       for ($curpos = tell(FILE); $_ = <FILE>;
                            $curpos = tell(FILE)) {
                           # search for some stuff and put it into files
                       }
                       sleep($for_a_while);
                       seek(FILE, $curpos, 0);
                   }

       seekdir DIRHANDLE,POS
               Sets the current position for the "readdir" routine on
               DIRHANDLE.  POS must be a value returned by "telldir".
               "seekdir" also has the same caveats about possible directory
               compaction as the corresponding system library routine.

       select FILEHANDLE
       select  Returns the currently selected filehandle.  If FILEHANDLE is
               supplied, sets the new current default filehandle for output.
               This has two effects: first, a "write" or a "print" without a
               filehandle will default to this FILEHANDLE.  Second, references
               to variables related to output will refer to this output
                   $oldfh = select(STDERR); $| = 1; select($oldfh);

               Some programmers may prefer to think of filehandles as objects
               with methods, preferring to write the last example as:

                   use IO::Handle;
                   STDERR->autoflush(1);

       select RBITS,WBITS,EBITS,TIMEOUT
               This calls the select(2) system call with the bit masks
               specified, which can be constructed using "fileno" and "vec",
               along these lines:

                   $rin = $win = $ein = '';
                   vec($rin,fileno(STDIN),1) = 1;
                   vec($win,fileno(STDOUT),1) = 1;
                   $ein = $rin | $win;

               If you want to select on many filehandles you might wish to
               write a subroutine:

                   sub fhbits {
                       my(@fhlist) = split(' ',$_[0]);
                       my($bits);
                       for (@fhlist) {
                           vec($bits,fileno($_),1) = 1;
                       }
                       $bits;
                   }
                   $rin = fhbits('STDIN TTY SOCK');

               The usual idiom is:

                   ($nfound,$timeleft) =
                     select($rout=$rin, $wout=$win, $eout=$ein, $timeout);

               or to block until something becomes ready just do this

                   $nfound = select($rout=$rin, $wout=$win, $eout=$ein, undef);

               Most systems do not bother to return anything useful in
               $timeleft, so calling select() in scalar context just returns
               $nfound.

               Any of the bit masks can also be undef.  The timeout, if
               specified, is in seconds, which may be fractional.  Note: not
               all implementations are capable of returning the $timeleft.  If
               not, they always return $timeleft equal to the supplied
               $timeout.

               You can effect a sleep of 250 milliseconds this way:

                   select(undef, undef, undef, 0.25);


               WARNING: One should not attempt to mix buffered I/O (like
               "read" or <FH>) with "select", except as permitted by POSIX,
               and even then only on POSIX systems.  You have to use "sysread"
               instead.

       semctl ID,SEMNUM,CMD,ARG
               Calls the System V IPC function "semctl".  You'll probably have
               to say

                   use IPC::SysV;

               first to get the correct constant definitions.  If CMD is
               IPC_STAT or GETALL, then ARG must be a variable that will hold
               the returned semid_ds structure or semaphore value array.
               Returns like "ioctl": the undefined value for error, ""0 but
               true"" for zero, or the actual return value otherwise.  The ARG
               must consist of a vector of native short integers, which may be
               created with "pack("s!",(0)x$nsem)".  See also "SysV IPC" in
               perlipc, "IPC::SysV", "IPC::Semaphore" documentation.

       semget KEY,NSEMS,FLAGS
               Calls the System V IPC function semget.  Returns the semaphore
               id, or the undefined value if there is an error.  See also
               "SysV IPC" in perlipc, "IPC::SysV", "IPC::SysV::Semaphore"
               documentation.

       semop KEY,OPSTRING
               Calls the System V IPC function semop to perform semaphore
               operations such as signalling and waiting.  OPSTRING must be a
               packed array of semop structures.  Each semop structure can be
               generated with "pack("s!3", $semnum, $semop, $semflag)".  The
               length of OPSTRING implies the number of semaphore operations.
               Returns true if successful, or false if there is an error.  As
               an example, the following code waits on semaphore $semnum of
               semaphore id $semid:

                   $semop = pack("s!3", $semnum, -1, 0);
                   die "Semaphore trouble: $!\n" unless semop($semid, $semop);

               To signal the semaphore, replace "-1" with 1.  See also "SysV
               IPC" in perlipc, "IPC::SysV", and "IPC::SysV::Semaphore"
               documentation.

       send SOCKET,MSG,FLAGS,TO
       send SOCKET,MSG,FLAGS
               Sends a message on a socket.  Attempts to send the scalar MSG
               to the SOCKET filehandle.  Takes the same flags as the system
               call of the same name.  On unconnected sockets you must specify
               a destination to send TO, in which case it does a C "sendto".
               Returns the number of characters sent, or the undefined value
               if there is an error.  The C system call sendmsg(2) is
               currently unimplemented.  See "UDP: Message Passing" in perlipc
               for examples.
               current process.  Will produce a fatal error if used on a
               machine that doesn't implement POSIX setpgid(2) or BSD
               setpgrp(2).  If the arguments are omitted, it defaults to
               "0,0".  Note that the BSD 4.2 version of "setpgrp" does not
               accept any arguments, so only "setpgrp(0,0)" is portable.  See
               also "POSIX::setsid()".

       setpriority WHICH,WHO,PRIORITY
               Sets the current priority for a process, a process group, or a
               user.  (See setpriority(2).)  Will produce a fatal error if
               used on a machine that doesn't implement setpriority(2).

       setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL
               Sets the socket option requested.  Returns undefined if there
               is an error.  Use integer constants provided by the "Socket"
               module for LEVEL and OPNAME.  Values for LEVEL can also be
               obtained from getprotobyname.  OPTVAL might either be a packed
               string or an integer.  An integer OPTVAL is shorthand for
               pack("i", OPTVAL).

               An example disabling the Nagle's algorithm for a socket:

                   use Socket qw(IPPROTO_TCP TCP_NODELAY);
                   setsockopt($socket, IPPROTO_TCP, TCP_NODELAY, 1);

       shift ARRAY
       shift   Shifts the first value of the array off and returns it,
               shortening the array by 1 and moving everything down.  If there
               are no elements in the array, returns the undefined value.  If
               ARRAY is omitted, shifts the @_ array within the lexical scope
               of subroutines and formats, and the @ARGV array outside of a
               subroutine and also within the lexical scopes established by
               the "eval STRING", "BEGIN {}", "INIT {}", "CHECK {}",
               "UNITCHECK {}" and "END {}" constructs.

               See also "unshift", "push", and "pop".  "shift" and "unshift"
               do the same thing to the left end of an array that "pop" and
               "push" do to the right end.

       shmctl ID,CMD,ARG
               Calls the System V IPC function shmctl.  You'll probably have
               to say

                   use IPC::SysV;

               first to get the correct constant definitions.  If CMD is
               "IPC_STAT", then ARG must be a variable that will hold the
               returned "shmid_ds" structure.  Returns like ioctl: the
               undefined value for error, "0 but true" for zero, or the actual
               return value otherwise.  See also "SysV IPC" in perlipc and
               "IPC::SysV" documentation.

       shmget KEY,SIZE,FLAGS
               Calls the System V IPC function shmget.  Returns the shared
               the variable. See also "SysV IPC" in perlipc, "IPC::SysV"
               documentation, and the "IPC::Shareable" module from CPAN.

       shutdown SOCKET,HOW
               Shuts down a socket connection in the manner indicated by HOW,
               which has the same interpretation as in the system call of the
               same name.

                   shutdown(SOCKET, 0);    # I/we have stopped reading data
                   shutdown(SOCKET, 1);    # I/we have stopped writing data
                   shutdown(SOCKET, 2);    # I/we have stopped using this socket

               This is useful with sockets when you want to tell the other
               side you're done writing but not done reading, or vice versa.
               It's also a more insistent form of close because it also
               disables the file descriptor in any forked copies in other
               processes.

               Returns 1 for success. In the case of error, returns "undef" if
               the first argument is not a valid filehandle, or returns 0 and
               sets $! for any other failure.

       sin EXPR
       sin     Returns the sine of EXPR (expressed in radians).  If EXPR is
               omitted, returns sine of $_.

               For the inverse sine operation, you may use the
               "Math::Trig::asin" function, or use this relation:

                   sub asin { atan2($_[0], sqrt(1 - $_[0] * $_[0])) }

       sleep EXPR
       sleep   Causes the script to sleep for EXPR seconds, or forever if no
               EXPR.  Returns the number of seconds actually slept.

               May be interrupted if the process receives a signal such as
               "SIGALRM".

                   eval {
                       local $SIG{ALARM} = sub { die "Alarm!\n" };
                       sleep;
                   };
                   die $@ unless $@ eq "Alarm!\n";

               You probably cannot mix "alarm" and "sleep" calls, because
               "sleep" is often implemented using "alarm".

               On some older systems, it may sleep up to a full second less
               than what you requested, depending on how it counts seconds.
               Most modern systems always sleep the full amount.  They may
               appear to sleep longer than that, however, because your process
               might not be scheduled right away in a busy multitasking
               system.

               filehandle SOCKET.  DOMAIN, TYPE, and PROTOCOL are specified
               the same as for the system call of the same name.  You should
               "use Socket" first to get the proper definitions imported.  See
               the examples in "Sockets: Client/Server Communication" in
               perlipc.

               On systems that support a close-on-exec flag on files, the flag
               will be set for the newly opened file descriptor, as determined
               by the value of $^F.  See "$^F" in perlvar.

       socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL
               Creates an unnamed pair of sockets in the specified domain, of
               the specified type.  DOMAIN, TYPE, and PROTOCOL are specified
               the same as for the system call of the same name.  If
               unimplemented, yields a fatal error.  Returns true if
               successful.

               On systems that support a close-on-exec flag on files, the flag
               will be set for the newly opened file descriptors, as
               determined by the value of $^F.  See "$^F" in perlvar.

               Some systems defined "pipe" in terms of "socketpair", in which
               a call to "pipe(Rdr, Wtr)" is essentially:

                   use Socket;
                   socketpair(Rdr, Wtr, AF_UNIX, SOCK_STREAM, PF_UNSPEC);
                   shutdown(Rdr, 1);        # no more writing for reader
                   shutdown(Wtr, 0);        # no more reading for writer

               See perlipc for an example of socketpair use.  Perl 5.8 and
               later will emulate socketpair using IP sockets to localhost if
               your system implements sockets but not socketpair.

       sort SUBNAME LIST
       sort BLOCK LIST
       sort LIST
               In list context, this sorts the LIST and returns the sorted
               list value.  In scalar context, the behaviour of "sort()" is
               undefined.

               If SUBNAME or BLOCK is omitted, "sort"s in standard string
               comparison order.  If SUBNAME is specified, it gives the name
               of a subroutine that returns an integer less than, equal to, or
               greater than 0, depending on how the elements of the list are
               to be ordered.  (The "<=>" and "cmp" operators are extremely
               useful in such routines.)  SUBNAME may be a scalar variable
               name (unsubscripted), in which case the value provides the name
               of (or a reference to) the actual subroutine to use.  In place
               of a SUBNAME, you can provide a BLOCK as an anonymous, in-line
               sort subroutine.

               If the subroutine's prototype is "($$)", the elements to be
               compared are passed by reference in @_, as for a normal
               subroutine.  This is slower than unprototyped subroutines,
               When "use locale" is in effect, "sort LIST" sorts LIST
               according to the current collation locale.  See perllocale.

               sort() returns aliases into the original list, much as a for
               loop's index variable aliases the list elements.  That is,
               modifying an element of a list returned by sort() (for example,
               in a "foreach", "map" or "grep") actually modifies the element
               in the original list.  This is usually something to be avoided
               when writing clear code.

               Perl 5.6 and earlier used a quicksort algorithm to implement
               sort.  That algorithm was not stable, and could go quadratic.
               (A stable sort preserves the input order of elements that
               compare equal.  Although quicksort's run time is O(NlogN) when
               averaged over all arrays of length N, the time can be O(N**2),
               quadratic behavior, for some inputs.)  In 5.7, the quicksort
               implementation was replaced with a stable mergesort algorithm
               whose worst-case behavior is O(NlogN).  But benchmarks
               indicated that for some inputs, on some platforms, the original
               quicksort was faster.  5.8 has a sort pragma for limited
               control of the sort.  Its rather blunt control of the
               underlying algorithm may not persist into future Perls, but the
               ability to characterize the input or output in implementation
               independent ways quite probably will.  See the sort pragma.

               Examples:

                   # sort lexically
                   @articles = sort @files;

                   # same thing, but with explicit sort routine
                   @articles = sort {$a cmp $b} @files;

                   # now case-insensitively
                   @articles = sort {uc($a) cmp uc($b)} @files;

                   # same thing in reversed order
                   @articles = sort {$b cmp $a} @files;

                   # sort numerically ascending
                   @articles = sort {$a <=> $b} @files;

                   # sort numerically descending
                   @articles = sort {$b <=> $a} @files;

                   # this sorts the %age hash by value instead of key
                   # using an in-line function
                   @eldest = sort { $age{$b} <=> $age{$a} } keys %age;

                   # sort using explicit subroutine name
                   sub byage {
                       $age{$a} <=> $age{$b};  # presuming numeric
                   }
                   @sortedclass = sort byage @class;
                   # the first integer after the first = sign, or the
                   # whole record case-insensitively otherwise

                   @new = sort {
                       ($b =~ /=(\d+)/)[0] <=> ($a =~ /=(\d+)/)[0]
                                           ||
                                   uc($a)  cmp  uc($b)
                   } @old;

                   # same thing, but much more efficiently;
                   # we'll build auxiliary indices instead
                   # for speed
                   @nums = @caps = ();
                   for (@old) {
                       push @nums, /=(\d+)/;
                       push @caps, uc($_);
                   }

                   @new = @old[ sort {
                                       $nums[$b] <=> $nums[$a]
                                                ||
                                       $caps[$a] cmp $caps[$b]
                                      } 0..$#old
                              ];

                   # same thing, but without any temps
                   @new = map { $_->[0] }
                          sort { $b->[1] <=> $a->[1]
                                          ||
                                 $a->[2] cmp $b->[2]
                          } map { [$_, /=(\d+)/, uc($_)] } @old;

                   # using a prototype allows you to use any comparison subroutine
                   # as a sort subroutine (including other package's subroutines)
                   package other;
                   sub backwards ($$) { $_[1] cmp $_[0]; }     # $a and $b are not set here

                   package main;
                   @new = sort other::backwards @old;

                   # guarantee stability, regardless of algorithm
                   use sort 'stable';
                   @new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old;

                   # force use of mergesort (not portable outside Perl 5.8)
                   use sort '_mergesort';  # note discouraging _
                   @new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old;

               Warning: syntactical care is required when sorting the list
               returned from a function. If you want to sort the list returned
               by the function call "find_records(@key)", you can use:

                   @contact = sort { $a cmp $b } find_records @key;
                   @contact = sort +find_records(@key);

               lexicals.  They are package globals.  That means that if you're
               in the "main" package and type

                   @articles = sort {$b <=> $a} @files;

               then $a and $b are $main::a and $main::b (or $::a and $::b),
               but if you're in the "FooPack" package, it's the same as typing

                   @articles = sort {$FooPack::b <=> $FooPack::a} @files;

               The comparison function is required to behave.  If it returns
               inconsistent results (sometimes saying $x[1] is less than $x[2]
               and sometimes saying the opposite, for example) the results are
               not well-defined.

               Because "<=>" returns "undef" when either operand is "NaN"
               (not-a-number), and because "sort" will trigger a fatal error
               unless the result of a comparison is defined, when sorting with
               a comparison function like "$a <=> $b", be careful about lists
               that might contain a "NaN".  The following example takes
               advantage of the fact that "NaN != NaN" to eliminate any "NaN"s
               from the input.

                   @result = sort { $a <=> $b } grep { $_ == $_ } @input;

       splice ARRAY,OFFSET,LENGTH,LIST
       splice ARRAY,OFFSET,LENGTH
       splice ARRAY,OFFSET
       splice ARRAY
               Removes the elements designated by OFFSET and LENGTH from an
               array, and replaces them with the elements of LIST, if any.  In
               list context, returns the elements removed from the array.  In
               scalar context, returns the last element removed, or "undef" if
               no elements are removed.  The array grows or shrinks as
               necessary.  If OFFSET is negative then it starts that far from
               the end of the array.  If LENGTH is omitted, removes everything
               from OFFSET onward.  If LENGTH is negative, removes the
               elements from OFFSET onward except for -LENGTH elements at the
               end of the array.  If both OFFSET and LENGTH are omitted,
               removes everything. If OFFSET is past the end of the array,
               perl issues a warning, and splices at the end of the array.

               The following equivalences hold (assuming "$[ == 0 and $#a >=
               $i" )

                   push(@a,$x,$y)      splice(@a,@a,0,$x,$y)
                   pop(@a)             splice(@a,-1)
                   shift(@a)           splice(@a,0,1)
                   unshift(@a,$x,$y)   splice(@a,0,0,$x,$y)
                   $a[$i] = $y         splice(@a,$i,1,$y)

               Example, assuming array lengths are passed before arrays:

                   sub aeq {   # compare two list values

       split /PATTERN/
       split   Splits the string EXPR into a list of strings and returns that
               list.  By default, empty leading fields are preserved, and
               empty trailing ones are deleted.  (If all fields are empty,
               they are considered to be trailing.)

               In scalar context, returns the number of fields found. In
               scalar and void context it splits into the @_ array.  Use of
               split in scalar and void context is deprecated, however,
               because it clobbers your subroutine arguments.

               If EXPR is omitted, splits the $_ string.  If PATTERN is also
               omitted, splits on whitespace (after skipping any leading
               whitespace).  Anything matching PATTERN is taken to be a
               delimiter separating the fields.  (Note that the delimiter may
               be longer than one character.)

               If LIMIT is specified and positive, it represents the maximum
               number of fields the EXPR will be split into, though the actual
               number of fields returned depends on the number of times
               PATTERN matches within EXPR.  If LIMIT is unspecified or zero,
               trailing null fields are stripped (which potential users of
               "pop" would do well to remember).  If LIMIT is negative, it is
               treated as if an arbitrarily large LIMIT had been specified.
               Note that splitting an EXPR that evaluates to the empty string
               always returns the empty list, regardless of the LIMIT
               specified.

               A pattern matching the null string (not to be confused with a
               null pattern "//", which is just one member of the set of
               patterns matching a null string) will split the value of EXPR
               into separate characters at each point it matches that way.
               For example:

                   print join(':', split(/ */, 'hi there')), "\n";

               produces the output 'h:i:t:h:e:r:e'.

               As a special case for "split", using the empty pattern "//"
               specifically matches only the null string, and is not be
               confused with the regular use of "//" to mean "the last
               successful pattern match".  So, for "split", the following:

                   print join(':', split(//, 'hi there')), "\n";

               produces the output 'h:i: :t:h:e:r:e'.

               Empty leading fields are produced when there are positive-width
               matches at the beginning of the string; a zero-width match at
               the beginning of the string does not produce an empty field.
               For example:

                  print join(':', split(/(?=\w)/, 'hi there!'));


                   ($login, $passwd, $remainder) = split(/:/, $_, 3);

               When assigning to a list, if LIMIT is omitted, or zero, Perl
               supplies a LIMIT one larger than the number of variables in the
               list, to avoid unnecessary work.  For the list above LIMIT
               would have been 4 by default.  In time critical applications it
               behooves you not to split into more fields than you really
               need.

               If the PATTERN contains parentheses, additional list elements
               are created from each matching substring in the delimiter.

                   split(/([,-])/, "1-10,20", 3);

               produces the list value

                   (1, '-', 10, ',', 20)

               If you had the entire header of a normal Unix email message in
               $header, you could split it up into fields and their values
               this way:

                   $header =~ s/\n(?=\s)//g;  # fix continuation lines
                   %hdrs   =  (UNIX_FROM => split /^(\S*?):\s*/m, $header);

               The pattern "/PATTERN/" may be replaced with an expression to
               specify patterns that vary at runtime.  (To do runtime
               compilation only once, use "/$variable/o".)

               As a special case, specifying a PATTERN of space (' ') will
               split on white space just as "split" with no arguments does.
               Thus, "split(' ')" can be used to emulate awk's default
               behavior, whereas "split(/ /)" will give you as many null
               initial fields as there are leading spaces.  A "split" on
               "/\s+/" is like a "split(' ')" except that any leading
               whitespace produces a null first field.  A "split" with no
               arguments really does a "split(' ', $_)" internally.

               A PATTERN of "/^/" is treated as if it were "/^/m", since it
               isn't much use otherwise.

               Example:

                   open(PASSWD, '/etc/passwd');
                   while (<PASSWD>) {
                       chomp;
                       ($login, $passwd, $uid, $gid,
                        $gcos, $home, $shell) = split(/:/);
                       #...
                   }

               As with regular pattern matching, any capturing parentheses
               that are not matched in a "split()" will be set to "undef" when

                       # Format number with up to 8 leading zeroes
                       $result = sprintf("%08d", $number);

                       # Round number to 3 digits after decimal point
                       $rounded = sprintf("%.3f", $number);

               Perl does its own "sprintf" formatting--it emulates the C
               function "sprintf", but it doesn't use it (except for floating-
               point numbers, and even then only the standard modifiers are
               allowed).  As a result, any non-standard extensions in your
               local "sprintf" are not available from Perl.

               Unlike "printf", "sprintf" does not do what you probably mean
               when you pass it an array as your first argument. The array is
               given scalar context, and instead of using the 0th element of
               the array as the format, Perl will use the count of elements in
               the array as the format, which is almost never useful.

               Perl's "sprintf" permits the following universally-known
               conversions:

                  %%   a percent sign
                  %c   a character with the given number
                  %s   a string
                  %d   a signed integer, in decimal
                  %u   an unsigned integer, in decimal
                  %o   an unsigned integer, in octal
                  %x   an unsigned integer, in hexadecimal
                  %e   a floating-point number, in scientific notation
                  %f   a floating-point number, in fixed decimal notation
                  %g   a floating-point number, in %e or %f notation

               In addition, Perl permits the following widely-supported
               conversions:

                  %X   like %x, but using upper-case letters
                  %E   like %e, but using an upper-case "E"
                  %G   like %g, but with an upper-case "E" (if applicable)
                  %b   an unsigned integer, in binary
                  %B   like %b, but using an upper-case "B" with the # flag
                  %p   a pointer (outputs the Perl value's address in hexadecimal)
                  %n   special: *stores* the number of characters output so far
                       into the next variable in the parameter list

               Finally, for backward (and we do mean "backward")
               compatibility, Perl permits these unnecessary but widely-
               supported conversions:

                  %i   a synonym for %d
                  %D   a synonym for %ld
                  %U   a synonym for %lu
                  %O   a synonym for %lo
                  %F   a synonym for %f

               format parameter index
                   An explicit format parameter index, such as "2$". By
                   default sprintf will format the next unused argument in the
                   list, but this allows you to take the arguments out of
                   order, e.g.:

                     printf '%2$d %1$d', 12, 34;      # prints "34 12"
                     printf '%3$d %d %1$d', 1, 2, 3;  # prints "3 1 1"

               flags
                   one or more of:

                      space   prefix non-negative number with a space
                      +       prefix non-negative number with a plus sign
                      -       left-justify within the field
                      0       use zeros, not spaces, to right-justify
                      #       ensure the leading "0" for any octal,
                              prefix non-zero hexadecimal with "0x" or "0X",
                              prefix non-zero binary with "0b" or "0B"

                   For example:

                     printf '<% d>',  12;   # prints "< 12>"
                     printf '<%+d>',  12;   # prints "<+12>"
                     printf '<%6s>',  12;   # prints "<    12>"
                     printf '<%-6s>', 12;   # prints "<12    >"
                     printf '<%06s>', 12;   # prints "<000012>"
                     printf '<%#o>',  12;   # prints "<014>"
                     printf '<%#x>',  12;   # prints "<0xc>"
                     printf '<%#X>',  12;   # prints "<0XC>"
                     printf '<%#b>',  12;   # prints "<0b1100>"
                     printf '<%#B>',  12;   # prints "<0B1100>"

                   When a space and a plus sign are given as the flags at
                   once, a plus sign is used to prefix a positive number.

                     printf '<%+ d>', 12;   # prints "<+12>"
                     printf '<% +d>', 12;   # prints "<+12>"

                   When the # flag and a precision are given in the %o
                   conversion, the precision is incremented if it's necessary
                   for the leading "0".

                     printf '<%#.5o>', 012;      # prints "<00012>"
                     printf '<%#.5o>', 012345;   # prints "<012345>"
                     printf '<%#.0o>', 0;        # prints "<0>"

               vector flag
                   This flag tells perl to interpret the supplied string as a
                   vector of integers, one for each character in the string.
                   Perl applies the format to each integer in turn, then joins
                   the resulting strings with a separator (a dot "." by
                   default). This can be useful for displaying ordinal values
                   of characters in arbitrary strings:

                     printf '%*4$vX %*4$vX %*4$vX', @addr[1..3], ":";   # 3 IPv6 addresses

               (minimum) width
                   Arguments are usually formatted to be only as wide as
                   required to display the given value. You can override the
                   width by putting a number here, or get the width from the
                   next argument (with "*") or from a specified argument (with
                   e.g. "*2$"):

                     printf '<%s>', "a";       # prints "<a>"
                     printf '<%6s>', "a";      # prints "<     a>"
                     printf '<%*s>', 6, "a";   # prints "<     a>"
                     printf '<%*2$s>', "a", 6; # prints "<     a>"
                     printf '<%2s>', "long";   # prints "<long>" (does not truncate)

                   If a field width obtained through "*" is negative, it has
                   the same effect as the "-" flag: left-justification.

               precision, or maximum width
                   You can specify a precision (for numeric conversions) or a
                   maximum width (for string conversions) by specifying a "."
                   followed by a number.  For floating point formats, with the
                   exception of 'g' and 'G', this specifies the number of
                   decimal places to show (the default being 6), e.g.:

                     # these examples are subject to system-specific variation
                     printf '<%f>', 1;    # prints "<1.000000>"
                     printf '<%.1f>', 1;  # prints "<1.0>"
                     printf '<%.0f>', 1;  # prints "<1>"
                     printf '<%e>', 10;   # prints "<1.000000e+01>"
                     printf '<%.1e>', 10; # prints "<1.0e+01>"

                   For 'g' and 'G', this specifies the maximum number of
                   digits to show, including prior to the decimal point as
                   well as after it, e.g.:

                     # these examples are subject to system-specific variation
                     printf '<%g>', 1;        # prints "<1>"
                     printf '<%.10g>', 1;     # prints "<1>"
                     printf '<%g>', 100;      # prints "<100>"
                     printf '<%.1g>', 100;    # prints "<1e+02>"
                     printf '<%.2g>', 100.01; # prints "<1e+02>"
                     printf '<%.5g>', 100.01; # prints "<100.01>"
                     printf '<%.4g>', 100.01; # prints "<100>"

                   For integer conversions, specifying a precision implies
                   that the output of the number itself should be zero-padded
                   to this width, where the 0 flag is ignored:

                     printf '<%.6d>', 1;      # prints "<000001>"
                     printf '<%+.6d>', 1;     # prints "<+000001>"
                     printf '<%-10.6d>', 1;   # prints "<000001    >"
                     printf '<%10.6d>', 1;    # prints "<    000001>"

                     printf '<%.5s>', "truncated";   # prints "<trunc>"
                     printf '<%10.5s>', "truncated"; # prints "<     trunc>"

                   You can also get the precision from the next argument using
                   ".*":

                     printf '<%.6x>', 1;       # prints "<000001>"
                     printf '<%.*x>', 6, 1;    # prints "<000001>"

                   If a precision obtained through "*" is negative, it has the
                   same effect as no precision.

                     printf '<%.*s>',  7, "string";   # prints "<string>"
                     printf '<%.*s>',  3, "string";   # prints "<str>"
                     printf '<%.*s>',  0, "string";   # prints "<>"
                     printf '<%.*s>', -1, "string";   # prints "<string>"

                     printf '<%.*d>',  1, 0;   # prints "<0>"
                     printf '<%.*d>',  0, 0;   # prints "<>"
                     printf '<%.*d>', -1, 0;   # prints "<0>"

                   You cannot currently get the precision from a specified
                   number, but it is intended that this will be possible in
                   the future using e.g. ".*2$":

                     printf '<%.*2$x>', 1, 6;   # INVALID, but in future will print "<000001>"

               size
                   For numeric conversions, you can specify the size to
                   interpret the number as using "l", "h", "V", "q", "L", or
                   "ll". For integer conversions ("d u o x X b i D U O"),
                   numbers are usually assumed to be whatever the default
                   integer size is on your platform (usually 32 or 64 bits),
                   but you can override this to use instead one of the
                   standard C types, as supported by the compiler used to
                   build Perl:

                      l           interpret integer as C type "long" or "unsigned long"
                      h           interpret integer as C type "short" or "unsigned short"
                      q, L or ll  interpret integer as C type "long long", "unsigned long long".
                                  or "quads" (typically 64-bit integers)

                   The last will produce errors if Perl does not understand
                   "quads" in your installation. (This requires that either
                   the platform natively supports quads or Perl was
                   specifically compiled to support quads.) You can find out
                   whether your Perl supports quads via Config:

                           use Config;
                           ($Config{use64bitint} eq 'define' || $Config{longsize} >= 8) &&
                                   print "quads\n";

                   For floating point conversions ("e f g E F G"), numbers are

                           use Config;
                           ($Config{uselongdouble} eq 'define') &&
                                   print "long doubles by default\n";

                   It can also be the case that long doubles and doubles are
                   the same thing:

                           use Config;
                           ($Config{doublesize} == $Config{longdblsize}) &&
                                   print "doubles are long doubles\n";

                   The size specifier "V" has no effect for Perl code, but it
                   is supported for compatibility with XS code; it means 'use
                   the standard size for a Perl integer (or floating-point
                   number)', which is already the default for Perl code.

               order of arguments
                   Normally, sprintf takes the next unused argument as the
                   value to format for each format specification. If the
                   format specification uses "*" to require additional
                   arguments, these are consumed from the argument list in the
                   order in which they appear in the format specification
                   before the value to format. Where an argument is specified
                   using an explicit index, this does not affect the normal
                   order for the arguments (even when the explicitly specified
                   index would have been the next argument in any case).

                   So:

                     printf '<%*.*s>', $a, $b, $c;

                   would use $a for the width, $b for the precision and $c as
                   the value to format, while:

                     printf '<%*1$.*s>', $a, $b;

                   would use $a for the width and the precision, and $b as the
                   value to format.

                   Here are some more examples - beware that when using an
                   explicit index, the "$" may need to be escaped:

                     printf "%2\$d %d\n",    12, 34;               # will print "34 12\n"
                     printf "%2\$d %d %d\n", 12, 34;               # will print "34 12 34\n"
                     printf "%3\$d %d %d\n", 12, 34, 56;           # will print "56 12 34\n"
                     printf "%2\$*3\$d %d\n", 12, 34, 3;           # will print " 34 12\n"

               If "use locale" is in effect, and POSIX::setlocale() has been
               called, the character used for the decimal separator in
               formatted floating point numbers is affected by the LC_NUMERIC
               locale.  See perllocale and POSIX.

       sqrt EXPR
               your program.

               If srand() is not called explicitly, it is called implicitly at
               the first use of the "rand" operator.  However, this was not
               the case in versions of Perl before 5.004, so if your script
               will run under older Perl versions, it should call "srand".

               Most programs won't even call srand() at all, except those that
               need a cryptographically-strong starting point rather than the
               generally acceptable default, which is based on time of day,
               process ID, and memory allocation, or the /dev/urandom device,
               if available.

               You can call srand($seed) with the same $seed to reproduce the
               same sequence from rand(), but this is usually reserved for
               generating predictable results for testing or debugging.
               Otherwise, don't call srand() more than once in your program.

               Do not call srand() (i.e. without an argument) more than once
               in a script.  The internal state of the random number generator
               should contain more entropy than can be provided by any seed,
               so calling srand() again actually loses randomness.

               Most implementations of "srand" take an integer and will
               silently truncate decimal numbers.  This means "srand(42)" will
               usually produce the same results as "srand(42.1)".  To be safe,
               always pass "srand" an integer.

               In versions of Perl prior to 5.004 the default seed was just
               the current "time".  This isn't a particularly good seed, so
               many old programs supply their own seed value (often "time ^
               $$" or "time ^ ($$ + ($$ << 15))"), but that isn't necessary
               any more.

               For cryptographic purposes, however, you need something much
               more random than the default seed.  Checksumming the compressed
               output of one or more rapidly changing operating system status
               programs is the usual method.  For example:

                   srand (time ^ $$ ^ unpack "%L*", `ps axww | gzip -f`);

               If you're particularly concerned with this, see the
               "Math::TrulyRandom" module in CPAN.

               Frequently called programs (like CGI scripts) that simply use

                   time ^ $$

               for a seed can fall prey to the mathematical property that

                   a^b == (a+1)^(b+1)

               one-third of the time.  So don't do that.

               Not all fields are supported on all filesystem types.  Here are
               the meanings of the fields:

                 0 dev      device number of filesystem
                 1 ino      inode number
                 2 mode     file mode  (type and permissions)
                 3 nlink    number of (hard) links to the file
                 4 uid      numeric user ID of file's owner
                 5 gid      numeric group ID of file's owner
                 6 rdev     the device identifier (special files only)
                 7 size     total size of file, in bytes
                 8 atime    last access time in seconds since the epoch
                 9 mtime    last modify time in seconds since the epoch
                10 ctime    inode change time in seconds since the epoch (*)
                11 blksize  preferred block size for file system I/O
                12 blocks   actual number of blocks allocated

               (The epoch was at 00:00 January 1, 1970 GMT.)

               (*) Not all fields are supported on all filesystem types.
               Notably, the ctime field is non-portable.  In particular, you
               cannot expect it to be a "creation time", see "Files and
               Filesystems" in perlport for details.

               If "stat" is passed the special filehandle consisting of an
               underline, no stat is done, but the current contents of the
               stat structure from the last "stat", "lstat", or filetest are
               returned.  Example:

                   if (-x $file && (($d) = stat(_)) && $d < 0) {
                       print "$file is executable NFS file\n";
                   }

               (This works on machines only for which the device number is
               negative under NFS.)

               Because the mode contains both the file type and its
               permissions, you should mask off the file type portion and
               (s)printf using a "%o" if you want to see the real permissions.

                   $mode = (stat($filename))[2];
                   printf "Permissions are %04o\n", $mode & 07777;

               In scalar context, "stat" returns a boolean value indicating
               success or failure, and, if successful, sets the information
               associated with the special filehandle "_".

               The File::stat module provides a convenient, by-name access
               mechanism:

                   use File::stat;
                   $sb = stat($filename);
                   printf "File is %s, size is %s, perm %04o, mtime %s\n",
                       $filename, $sb->size, $sb->mode & 07777,

                   printf "Permissions are %04o\n", S_IMODE($mode), "\n";

                   $is_setuid     =  $mode & S_ISUID;
                   $is_directory  =  S_ISDIR($mode);

               You could write the last two using the "-u" and "-d" operators.
               The commonly available "S_IF*" constants are

                   # Permissions: read, write, execute, for user, group, others.

                   S_IRWXU S_IRUSR S_IWUSR S_IXUSR
                   S_IRWXG S_IRGRP S_IWGRP S_IXGRP
                   S_IRWXO S_IROTH S_IWOTH S_IXOTH

                   # Setuid/Setgid/Stickiness/SaveText.
                   # Note that the exact meaning of these is system dependent.

                   S_ISUID S_ISGID S_ISVTX S_ISTXT

                   # File types.  Not necessarily all are available on your system.

                   S_IFREG S_IFDIR S_IFLNK S_IFBLK S_IFCHR S_IFIFO S_IFSOCK S_IFWHT S_ENFMT

                   # The following are compatibility aliases for S_IRUSR, S_IWUSR, S_IXUSR.

                   S_IREAD S_IWRITE S_IEXEC

               and the "S_IF*" functions are

                   S_IMODE($mode)      the part of $mode containing the permission bits
                                       and the setuid/setgid/sticky bits

                   S_IFMT($mode)       the part of $mode containing the file type
                                       which can be bit-anded with e.g. S_IFREG
                                       or with the following functions

                   # The operators -f, -d, -l, -b, -c, -p, and -S.

                   S_ISREG($mode) S_ISDIR($mode) S_ISLNK($mode)
                   S_ISBLK($mode) S_ISCHR($mode) S_ISFIFO($mode) S_ISSOCK($mode)

                   # No direct -X operator counterpart, but for the first one
                   # the -g operator is often equivalent.  The ENFMT stands for
                   # record flocking enforcement, a platform-dependent feature.

                   S_ISENFMT($mode) S_ISWHT($mode)

               See your native chmod(2) and stat(2) documentation for more
               details about the "S_*" constants.  To get status info for a
               symbolic link instead of the target file behind the link, use
               the "lstat" function.

       state EXPR
       study   Takes extra time to study SCALAR ($_ if unspecified) in
               anticipation of doing many pattern matches on the string before
               it is next modified.  This may or may not save time, depending
               on the nature and number of patterns you are searching on, and
               on the distribution of character frequencies in the string to
               be searched--you probably want to compare run times with and
               without it to see which runs faster.  Those loops that scan for
               many short constant strings (including the constant parts of
               more complex patterns) will benefit most.  You may have only
               one "study" active at a time--if you study a different scalar
               the first is "unstudied".  (The way "study" works is this: a
               linked list of every character in the string to be searched is
               made, so we know, for example, where all the 'k' characters
               are.  From each search string, the rarest character is
               selected, based on some static frequency tables constructed
               from some C programs and English text.  Only those places that
               contain this "rarest" character are examined.)

               For example, here is a loop that inserts index producing
               entries before any line containing a certain pattern:

                   while (<>) {
                       study;
                       print ".IX foo\n"       if /\bfoo\b/;
                       print ".IX bar\n"       if /\bbar\b/;
                       print ".IX blurfl\n"    if /\bblurfl\b/;
                       # ...
                       print;
                   }

               In searching for "/\bfoo\b/", only those locations in $_ that
               contain "f" will be looked at, because "f" is rarer than "o".
               In general, this is a big win except in pathological cases.
               The only question is whether it saves you more time than it
               took to build the linked list in the first place.

               Note that if you have to look for strings that you don't know
               till runtime, you can build an entire loop as a string and
               "eval" that to avoid recompiling all your patterns all the
               time.  Together with undefining $/ to input entire files as one
               record, this can be very fast, often faster than specialized
               programs like fgrep(1).  The following scans a list of files
               (@files) for a list of words (@words), and prints out the names
               of those files that contain a match:

                   $search = 'while (<>) { study;';
                   foreach $word (@words) {
                       $search .= "++\$seen{\$ARGV} if /\\b$word\\b/;\n";
                   }
                   $search .= "}";
                   @ARGV = @files;
                   undef $/;
                   eval $search;               # this screams
                   $/ = "\n";          # put back to normal input delimiter

               See perlsub and perlref for details about subroutines and
               references, and attributes and Attribute::Handlers for more
               information about attributes.

       substr EXPR,OFFSET,LENGTH,REPLACEMENT
       substr EXPR,OFFSET,LENGTH
       substr EXPR,OFFSET
               Extracts a substring out of EXPR and returns it.  First
               character is at offset 0, or whatever you've set $[ to (but
               don't do that).  If OFFSET is negative (or more precisely, less
               than $[), starts that far from the end of the string.  If
               LENGTH is omitted, returns everything to the end of the string.
               If LENGTH is negative, leaves that many characters off the end
               of the string.

                   my $s = "The black cat climbed the green tree";
                   my $color  = substr $s, 4, 5;       # black
                   my $middle = substr $s, 4, -11;     # black cat climbed the
                   my $end    = substr $s, 14;         # climbed the green tree
                   my $tail   = substr $s, -4;         # tree
                   my $z      = substr $s, -4, 2;      # tr

               You can use the substr() function as an lvalue, in which case
               EXPR must itself be an lvalue.  If you assign something shorter
               than LENGTH, the string will shrink, and if you assign
               something longer than LENGTH, the string will grow to
               accommodate it.  To keep the string the same length you may
               need to pad or chop your value using "sprintf".

               If OFFSET and LENGTH specify a substring that is partly outside
               the string, only the part within the string is returned.  If
               the substring is beyond either end of the string, substr()
               returns the undefined value and produces a warning.  When used
               as an lvalue, specifying a substring that is entirely outside
               the string is a fatal error.  Here's an example showing the
               behavior for boundary cases:

                   my $name = 'fred';
                   substr($name, 4) = 'dy';            # $name is now 'freddy'
                   my $null = substr $name, 6, 2;      # returns '' (no warning)
                   my $oops = substr $name, 7;         # returns undef, with warning
                   substr($name, 7) = 'gap';           # fatal error

               An alternative to using substr() as an lvalue is to specify the
               replacement string as the 4th argument.  This allows you to
               replace parts of the EXPR and return what was there before in
               one operation, just as you can with splice().

                   my $s = "The black cat climbed the green tree";
                   my $z = substr $s, 14, 7, "jumped from";    # climbed
                   # $s is now "The black cat jumped from the green tree"

               Note that the lvalue returned by the 3-arg version of substr()
               Prior to Perl version 5.9.1, the result of using an lvalue
               multiple times was unspecified.

       symlink OLDFILE,NEWFILE
               Creates a new filename symbolically linked to the old filename.
               Returns 1 for success, 0 otherwise.  On systems that don't
               support symbolic links, produces a fatal error at run time.  To
               check for that, use eval:

                   $symlink_exists = eval { symlink("",""); 1 };

       syscall NUMBER, LIST
               Calls the system call specified as the first element of the
               list, passing the remaining elements as arguments to the system
               call.  If unimplemented, produces a fatal error.  The arguments
               are interpreted as follows: if a given argument is numeric, the
               argument is passed as an int.  If not, the pointer to the
               string value is passed.  You are responsible to make sure a
               string is pre-extended long enough to receive any result that
               might be written into a string.  You can't use a string literal
               (or other read-only string) as an argument to "syscall" because
               Perl has to assume that any string pointer might be written
               through.  If your integer arguments are not literals and have
               never been interpreted in a numeric context, you may need to
               add 0 to them to force them to look like numbers.  This
               emulates the "syswrite" function (or vice versa):

                   require 'syscall.ph';               # may need to run h2ph
                   $s = "hi there\n";
                   syscall(&SYS_write, fileno(STDOUT), $s, length $s);

               Note that Perl supports passing of up to only 14 arguments to
               your system call, which in practice should usually suffice.

               Syscall returns whatever value returned by the system call it
               calls.  If the system call fails, "syscall" returns "-1" and
               sets $! (errno).  Note that some system calls can legitimately
               return "-1".  The proper way to handle such calls is to assign
               "$!=0;" before the call and check the value of $! if syscall
               returns "-1".

               There's a problem with "syscall(&SYS_pipe)": it returns the
               file number of the read end of the pipe it creates.  There is
               no way to retrieve the file number of the other end.  You can
               avoid this problem by using "pipe" instead.

       sysopen FILEHANDLE,FILENAME,MODE
       sysopen FILEHANDLE,FILENAME,MODE,PERMS
               Opens the file whose filename is given by FILENAME, and
               associates it with FILEHANDLE.  If FILEHANDLE is an expression,
               its value is used as the name of the real filehandle wanted.
               This function calls the underlying operating system's "open"
               function with the parameters FILENAME, MODE, PERMS.

               supported by perl: zero means read-only, one means write-only,
               and two means read/write.  We know that these values do not
               work under OS/390 & VM/ESA Unix and on the Macintosh; you
               probably don't want to use them in new code.

               If the file named by FILENAME does not exist and the "open"
               call creates it (typically because MODE includes the "O_CREAT"
               flag), then the value of PERMS specifies the permissions of the
               newly created file.  If you omit the PERMS argument to
               "sysopen", Perl uses the octal value 0666.  These permission
               values need to be in octal, and are modified by your process's
               current "umask".

               In many systems the "O_EXCL" flag is available for opening
               files in exclusive mode.  This is not locking: exclusiveness
               means here that if the file already exists, sysopen() fails.
               "O_EXCL" may not work on network filesystems, and has no effect
               unless the "O_CREAT" flag is set as well.  Setting
               "O_CREAT|O_EXCL" prevents the file from being opened if it is a
               symbolic link.  It does not protect against symbolic links in
               the file's path.

               Sometimes you may want to truncate an already-existing file.
               This can be done using the "O_TRUNC" flag.  The behavior of
               "O_TRUNC" with "O_RDONLY" is undefined.

               You should seldom if ever use 0644 as argument to "sysopen",
               because that takes away the user's option to have a more
               permissive umask.  Better to omit it.  See the perlfunc(1)
               entry on "umask" for more on this.

               Note that "sysopen" depends on the fdopen() C library function.
               On many UNIX systems, fdopen() is known to fail when file
               descriptors exceed a certain value, typically 255. If you need
               more file descriptors than that, consider rebuilding Perl to
               use the "sfio" library, or perhaps using the POSIX::open()
               function.

               See perlopentut for a kinder, gentler explanation of opening
               files.

       sysread FILEHANDLE,SCALAR,LENGTH,OFFSET
       sysread FILEHANDLE,SCALAR,LENGTH
               Attempts to read LENGTH bytes of data into variable SCALAR from
               the specified FILEHANDLE, using the system call read(2).  It
               bypasses buffered IO, so mixing this with other kinds of reads,
               "print", "write", "seek", "tell", or "eof" can cause confusion
               because the perlio or stdio layers usually buffers data.
               Returns the number of bytes actually read, 0 at end of file, or
               undef if there was an error (in the latter case $! is also
               set).  SCALAR will be grown or shrunk so that the last byte
               actually read is the last byte of the scalar after the read.

               An OFFSET may be specified to place the read data at some place
               Note that if the filehandle has been marked as ":utf8" Unicode
               characters are read instead of bytes (the LENGTH, OFFSET, and
               the return value of sysread() are in Unicode characters).  The
               ":encoding(...)" layer implicitly introduces the ":utf8" layer.
               See "binmode", "open", and the "open" pragma, open.

       sysseek FILEHANDLE,POSITION,WHENCE
               Sets FILEHANDLE's system position in bytes using the system
               call lseek(2).  FILEHANDLE may be an expression whose value
               gives the name of the filehandle.  The values for WHENCE are 0
               to set the new position to POSITION, 1 to set the it to the
               current position plus POSITION, and 2 to set it to EOF plus
               POSITION (typically negative).

               Note the in bytes: even if the filehandle has been set to
               operate on characters (for example by using the
               ":encoding(utf8)" I/O layer), tell() will return byte offsets,
               not character offsets (because implementing that would render
               sysseek() very slow).

               sysseek() bypasses normal buffered IO, so mixing this with
               reads (other than "sysread", for example "<>" or read())
               "print", "write", "seek", "tell", or "eof" may cause confusion.

               For WHENCE, you may also use the constants "SEEK_SET",
               "SEEK_CUR", and "SEEK_END" (start of the file, current
               position, end of the file) from the Fcntl module.  Use of the
               constants is also more portable than relying on 0, 1, and 2.
               For example to define a "systell" function:

                       use Fcntl 'SEEK_CUR';
                       sub systell { sysseek($_[0], 0, SEEK_CUR) }

               Returns the new position, or the undefined value on failure.  A
               position of zero is returned as the string "0 but true"; thus
               "sysseek" returns true on success and false on failure, yet you
               can still easily determine the new position.

       system LIST
       system PROGRAM LIST
               Does exactly the same thing as "exec LIST", except that a fork
               is done first, and the parent process waits for the child
               process to complete.  Note that argument processing varies
               depending on the number of arguments.  If there is more than
               one argument in LIST, or if LIST is an array with more than one
               value, starts the program given by the first element of the
               list with arguments given by the rest of the list.  If there is
               only one scalar argument, the argument is checked for shell
               metacharacters, and if there are any, the entire argument is
               passed to the system's command shell for parsing (this is
               "/bin/sh -c" on Unix platforms, but varies on other platforms).
               If there are no shell metacharacters in the argument, it is
               split into words and passed directly to "execvp", which is more
               efficient.
               "`STRING`" in perlop.  Return value of -1 indicates a failure
               to start the program or an error of the wait(2) system call
               (inspect $! for the reason).

               If you'd like to make "system" (and many other bits of Perl)
               die on error, have a look at the autodie pragma.

               Like "exec", "system" allows you to lie to a program about its
               name if you use the "system PROGRAM LIST" syntax.  Again, see
               "exec".

               Since "SIGINT" and "SIGQUIT" are ignored during the execution
               of "system", if you expect your program to terminate on receipt
               of these signals you will need to arrange to do so yourself
               based on the return value.

                   @args = ("command", "arg1", "arg2");
                   system(@args) == 0
                        or die "system @args failed: $?"

               If you'd like to manually inspect "system"'s failure, you can
               check all possible failure modes by inspecting $? like this:

                   if ($? == -1) {
                       print "failed to execute: $!\n";
                   }
                   elsif ($? & 127) {
                       printf "child died with signal %d, %s coredump\n",
                           ($? & 127),  ($? & 128) ? 'with' : 'without';
                   }
                   else {
                       printf "child exited with value %d\n", $? >> 8;
                   }

               Alternatively you might inspect the value of
               "${^CHILD_ERROR_NATIVE}" with the W*() calls of the POSIX
               extension.

               When the arguments get executed via the system shell, results
               and return codes will be subject to its quirks and
               capabilities.  See "`STRING`" in perlop and "exec" for details.

       syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET
       syswrite FILEHANDLE,SCALAR,LENGTH
       syswrite FILEHANDLE,SCALAR
               Attempts to write LENGTH bytes of data from variable SCALAR to
               the specified FILEHANDLE, using the system call write(2).  If
               LENGTH is not specified, writes whole SCALAR.  It bypasses
               buffered IO, so mixing this with reads (other than sysread()),
               "print", "write", "seek", "tell", or "eof" may cause confusion
               because the perlio and stdio layers usually buffers data.
               Returns the number of bytes actually written, or "undef" if
               there was an error (in this case the errno variable $! is also
               set).  If the LENGTH is greater than the available data in the
               characters).  The ":encoding(...)" layer implicitly introduces
               the ":utf8" layer.  See "binmode", "open", and the "open"
               pragma, open.

       tell FILEHANDLE
       tell    Returns the current position in bytes for FILEHANDLE, or -1 on
               error.  FILEHANDLE may be an expression whose value gives the
               name of the actual filehandle.  If FILEHANDLE is omitted,
               assumes the file last read.

               Note the in bytes: even if the filehandle has been set to
               operate on characters (for example by using the
               ":encoding(utf8)" open layer), tell() will return byte offsets,
               not character offsets (because that would render seek() and
               tell() rather slow).

               The return value of tell() for the standard streams like the
               STDIN depends on the operating system: it may return -1 or
               something else.  tell() on pipes, fifos, and sockets usually
               returns -1.

               There is no "systell" function.  Use "sysseek(FH, 0, 1)" for
               that.

               Do not use tell() (or other buffered I/O operations) on a file
               handle that has been manipulated by sysread(), syswrite() or
               sysseek().  Those functions ignore the buffering, while tell()
               does not.

       telldir DIRHANDLE
               Returns the current position of the "readdir" routines on
               DIRHANDLE.  Value may be given to "seekdir" to access a
               particular location in a directory.  "telldir" has the same
               caveats about possible directory compaction as the
               corresponding system library routine.

       tie VARIABLE,CLASSNAME,LIST
               This function binds a variable to a package class that will
               provide the implementation for the variable.  VARIABLE is the
               name of the variable to be enchanted.  CLASSNAME is the name of
               a class implementing objects of correct type.  Any additional
               arguments are passed to the "new" method of the class (meaning
               "TIESCALAR", "TIEHANDLE", "TIEARRAY", or "TIEHASH").  Typically
               these are arguments such as might be passed to the "dbm_open()"
               function of C.  The object returned by the "new" method is also
               returned by the "tie" function, which would be useful if you
               want to access other methods in CLASSNAME.

               Note that functions such as "keys" and "values" may return huge
               lists when used on large objects, like DBM files.  You may
               prefer to use the "each" function to iterate over such.
               Example:

                   # print out history file offsets
                   DELETE this, key
                   CLEAR this
                   EXISTS this, key
                   FIRSTKEY this
                   NEXTKEY this, lastkey
                   SCALAR this
                   DESTROY this
                   UNTIE this

               A class implementing an ordinary array should have the
               following methods:

                   TIEARRAY classname, LIST
                   FETCH this, key
                   STORE this, key, value
                   FETCHSIZE this
                   STORESIZE this, count
                   CLEAR this
                   PUSH this, LIST
                   POP this
                   SHIFT this
                   UNSHIFT this, LIST
                   SPLICE this, offset, length, LIST
                   EXTEND this, count
                   DESTROY this
                   UNTIE this

               A class implementing a file handle should have the following
               methods:

                   TIEHANDLE classname, LIST
                   READ this, scalar, length, offset
                   READLINE this
                   GETC this
                   WRITE this, scalar, length, offset
                   PRINT this, LIST
                   PRINTF this, format, LIST
                   BINMODE this
                   EOF this
                   FILENO this
                   SEEK this, position, whence
                   TELL this
                   OPEN this, mode, LIST
                   CLOSE this
                   DESTROY this
                   UNTIE this

               A class implementing a scalar should have the following
               methods:

                   TIESCALAR classname, LIST
                   FETCH this,
                   STORE this, value
                   DESTROY this

       tied VARIABLE
               Returns a reference to the object underlying VARIABLE (the same
               value that was originally returned by the "tie" call that bound
               the variable to a package.)  Returns the undefined value if
               VARIABLE isn't tied to a package.

       time    Returns the number of non-leap seconds since whatever time the
               system considers to be the epoch, suitable for feeding to
               "gmtime" and "localtime". On most systems the epoch is 00:00:00
               UTC, January 1, 1970; a prominent exception being Mac OS
               Classic which uses 00:00:00, January 1, 1904 in the current
               local time zone for its epoch.

               For measuring time in better granularity than one second, you
               may use either the Time::HiRes module (from CPAN, and starting
               from Perl 5.8 part of the standard distribution), or if you
               have gettimeofday(2), you may be able to use the "syscall"
               interface of Perl.  See perlfaq8 for details.

               For date and time processing look at the many related modules
               on CPAN.  For a comprehensive date and time representation look
               at the DateTime module.

       times   Returns a four-element list giving the user and system times,
               in seconds, for this process and the children of this process.

                   ($user,$system,$cuser,$csystem) = times;

               In scalar context, "times" returns $user.

               Note that times for children are included only after they
               terminate.

       tr///   The transliteration operator.  Same as "y///".  See "Quote and
               Quote-like Operators" in perlop.

       truncate FILEHANDLE,LENGTH
       truncate EXPR,LENGTH
               Truncates the file opened on FILEHANDLE, or named by EXPR, to
               the specified length.  Produces a fatal error if truncate isn't
               implemented on your system.  Returns true if successful, the
               undefined value otherwise.

               The behavior is undefined if LENGTH is greater than the length
               of the file.

               The position in the file of FILEHANDLE is left unchanged.  You
               may want to call seek before writing to the file.

       uc EXPR
       uc      Returns an uppercased version of EXPR.  This is the internal
               function implementing the "\U" escape in double-quoted strings.
               Respects current LC_CTYPE locale if "use locale" in force.  See
               perllocale and perlunicode for more details about locale and

               If EXPR is omitted, uses $_.

       umask EXPR
       umask   Sets the umask for the process to EXPR and returns the previous
               value.  If EXPR is omitted, merely returns the current umask.

               The Unix permission "rwxr-x---" is represented as three sets of
               three bits, or three octal digits: 0750 (the leading 0
               indicates octal and isn't one of the digits).  The "umask"
               value is such a number representing disabled permissions bits.
               The permission (or "mode") values you pass "mkdir" or "sysopen"
               are modified by your umask, so even if you tell "sysopen" to
               create a file with permissions 0777, if your umask is 0022 then
               the file will actually be created with permissions 0755.  If
               your "umask" were 0027 (group can't write; others can't read,
               write, or execute), then passing "sysopen" 0666 would create a
               file with mode 0640 ("0666 &~ 027" is 0640).

               Here's some advice: supply a creation mode of 0666 for regular
               files (in "sysopen") and one of 0777 for directories (in
               "mkdir") and executable files.  This gives users the freedom of
               choice: if they want protected files, they might choose process
               umasks of 022, 027, or even the particularly antisocial mask of
               077.  Programs should rarely if ever make policy decisions
               better left to the user.  The exception to this is when writing
               files that should be kept private: mail files, web browser
               cookies, .rhosts files, and so on.

               If umask(2) is not implemented on your system and you are
               trying to restrict access for yourself (i.e., (EXPR & 0700) >
               0), produces a fatal error at run time.  If umask(2) is not
               implemented and you are not trying to restrict access for
               yourself, returns "undef".

               Remember that a umask is a number, usually given in octal; it
               is not a string of octal digits.  See also "oct", if all you
               have is a string.

       undef EXPR
       undef   Undefines the value of EXPR, which must be an lvalue.  Use only
               on a scalar value, an array (using "@"), a hash (using "%"), a
               subroutine (using "&"), or a typeglob (using "*").  (Saying
               "undef $hash{$key}" will probably not do what you expect on
               most predefined variables or DBM list values, so don't do that;
               see delete.)  Always returns the undefined value.  You can omit
               the EXPR, in which case nothing is undefined, but you still get
               an undefined value that you could, for instance, return from a
               subroutine, assign to a variable or pass as a parameter.
               Examples:

                   undef $foo;
                   undef $bar{'blurfl'};      # Compare to: delete $bar{'blurfl'};
                   undef @ary;

                   $cnt = unlink 'a', 'b', 'c';
                   unlink @goners;
                   unlink <*.bak>;

               Note: "unlink" will not attempt to delete directories unless
               you are superuser and the -U flag is supplied to Perl.  Even if
               these conditions are met, be warned that unlinking a directory
               can inflict damage on your filesystem.  Finally, using "unlink"
               on directories is not supported on many operating systems.  Use
               "rmdir" instead.

               If LIST is omitted, uses $_.

       unpack TEMPLATE,EXPR
       unpack TEMPLATE
               "unpack" does the reverse of "pack": it takes a string and
               expands it out into a list of values.  (In scalar context, it
               returns merely the first value produced.)

               If EXPR is omitted, unpacks the $_ string.

               The string is broken into chunks described by the TEMPLATE.
               Each chunk is converted separately to a value.  Typically,
               either the string is a result of "pack", or the characters of
               the string represent a C structure of some kind.

               The TEMPLATE has the same format as in the "pack" function.
               Here's a subroutine that does substring:

                   sub substr {
                       my($what,$where,$howmuch) = @_;
                       unpack("x$where a$howmuch", $what);
                   }

               and then there's

                   sub ordinal { unpack("W",$_[0]); } # same as ord()

               In addition to fields allowed in pack(), you may prefix a field
               with a %<number> to indicate that you want a <number>-bit
               checksum of the items instead of the items themselves.  Default
               is a 16-bit checksum.  Checksum is calculated by summing
               numeric values of expanded values (for string fields the sum of
               "ord($char)" is taken, for bit fields the sum of zeroes and
               ones).

               For example, the following computes the same number as the
               System V sum program:

                   $checksum = do {
                       local $/;  # slurp!
                       unpack("%32W*",<>) % 65535;
                   };

               If there are more pack codes or if the repeat count of a field
               or a group is larger than what the remainder of the input
               string allows, the result is not well defined: in some cases,
               the repeat count is decreased, or "unpack()" will produce null
               strings or zeroes, or terminate with an error. If the input
               string is longer than one described by the TEMPLATE, the rest
               is ignored.

               See "pack" for more examples and notes.

       untie VARIABLE
               Breaks the binding between a variable and a package.  (See
               "tie".)  Has no effect if the variable is not tied.

       unshift ARRAY,LIST
               Does the opposite of a "shift".  Or the opposite of a "push",
               depending on how you look at it.  Prepends list to the front of
               the array, and returns the new number of elements in the array.

                   unshift(@ARGV, '-e') unless $ARGV[0] =~ /^-/;

               Note the LIST is prepended whole, not one element at a time, so
               the prepended elements stay in the same order.  Use "reverse"
               to do the reverse.

       use Module VERSION LIST
       use Module VERSION
       use Module LIST
       use Module
       use VERSION
               Imports some semantics into the current package from the named
               module, generally by aliasing certain subroutine or variable
               names into your package.  It is exactly equivalent to

                   BEGIN { require Module; Module->import( LIST ); }

               except that Module must be a bareword.

               In the peculiar "use VERSION" form, VERSION may be either a
               numeric argument such as 5.006, which will be compared to $],
               or a literal of the form v5.6.1, which will be compared to $^V
               (aka $PERL_VERSION).  A fatal error is produced if VERSION is
               greater than the version of the current Perl interpreter; Perl
               will not attempt to parse the rest of the file.  Compare with
               "require", which can do a similar check at run time.
               Symmetrically, "no VERSION" allows you to specify that you want
               a version of perl older than the specified one.

               Specifying VERSION as a literal of the form v5.6.1 should
               generally be avoided, because it leads to misleading error
               messages under earlier versions of Perl (that is, prior to
               5.6.0) that do not support this syntax.  The equivalent numeric
               version should be used instead.

               feature.

               The "BEGIN" forces the "require" and "import" to happen at
               compile time.  The "require" makes sure the module is loaded
               into memory if it hasn't been yet.  The "import" is not a
               builtin--it's just an ordinary static method call into the
               "Module" package to tell the module to import the list of
               features back into the current package.  The module can
               implement its "import" method any way it likes, though most
               modules just choose to derive their "import" method via
               inheritance from the "Exporter" class that is defined in the
               "Exporter" module.  See Exporter.  If no "import" method can be
               found then the call is skipped, even if there is an AUTOLOAD
               method.

               If you do not want to call the package's "import" method (for
               instance, to stop your namespace from being altered),
               explicitly supply the empty list:

                   use Module ();

               That is exactly equivalent to

                   BEGIN { require Module }

               If the VERSION argument is present between Module and LIST,
               then the "use" will call the VERSION method in class Module
               with the given version as an argument.  The default VERSION
               method, inherited from the UNIVERSAL class, croaks if the given
               version is larger than the value of the variable
               $Module::VERSION.

               Again, there is a distinction between omitting LIST ("import"
               called with no arguments) and an explicit empty LIST "()"
               ("import" not called).  Note that there is no comma after
               VERSION!

               Because this is a wide-open interface, pragmas (compiler
               directives) are also implemented this way.  Currently
               implemented pragmas are:

                   use constant;
                   use diagnostics;
                   use integer;
                   use sigtrap  qw(SEGV BUS);
                   use strict   qw(subs vars refs);
                   use subs     qw(afunc blurfl);
                   use warnings qw(all);
                   use sort     qw(stable _quicksort _mergesort);

               Some of these pseudo-modules import semantics into the current
               block scope (like "strict" or "integer", unlike ordinary
               modules, which import symbols into the current package (which
               are effective through the end of the file).
               perlrun for the "-M" and "-m" command-line options to perl that
               give "use" functionality from the command-line.

       utime LIST
               Changes the access and modification times on each file of a
               list of files.  The first two elements of the list must be the
               NUMERICAL access and modification times, in that order.
               Returns the number of files successfully changed.  The inode
               change time of each file is set to the current time.  For
               example, this code has the same effect as the Unix touch(1)
               command when the files already exist and belong to the user
               running the program:

                   #!/usr/bin/perl
                   $atime = $mtime = time;
                   utime $atime, $mtime, @ARGV;

               Since perl 5.7.2, if the first two elements of the list are
               "undef", then the utime(2) function in the C library will be
               called with a null second argument. On most systems, this will
               set the file's access and modification times to the current
               time (i.e. equivalent to the example above) and will even work
               on other users' files where you have write permission:

                   utime undef, undef, @ARGV;

               Under NFS this will use the time of the NFS server, not the
               time of the local machine.  If there is a time synchronization
               problem, the NFS server and local machine will have different
               times.  The Unix touch(1) command will in fact normally use
               this form instead of the one shown in the first example.

               Note that only passing one of the first two elements as "undef"
               will be equivalent of passing it as 0 and will not have the
               same effect as described when they are both "undef".  This case
               will also trigger an uninitialized warning.

               On systems that support futimes, you might pass file handles
               among the files.  On systems that don't support futimes,
               passing file handles produces a fatal error at run time.  The
               file handles must be passed as globs or references to be
               recognized.  Barewords are considered file names.

       values HASH
               Returns a list consisting of all the values of the named hash.
               (In a scalar context, returns the number of values.)

               The values are returned in an apparently random order.  The
               actual random order is subject to change in future versions of
               perl, but it is guaranteed to be the same order as either the
               "keys" or "each" function would produce on the same
               (unmodified) hash.  Since Perl 5.8.1 the ordering is different
               even between different runs of Perl for security reasons (see
               "Algorithmic Complexity Attacks" in perlsec).

       vec EXPR,OFFSET,BITS
               Treats the string in EXPR as a bit vector made up of elements
               of width BITS, and returns the value of the element specified
               by OFFSET as an unsigned integer.  BITS therefore specifies the
               number of bits that are reserved for each element in the bit
               vector.  This must be a power of two from 1 to 32 (or 64, if
               your platform supports that).

               If BITS is 8, "elements" coincide with bytes of the input
               string.

               If BITS is 16 or more, bytes of the input string are grouped
               into chunks of size BITS/8, and each group is converted to a
               number as with pack()/unpack() with big-endian formats "n"/"N"
               (and analogously for BITS==64).  See "pack" for details.

               If bits is 4 or less, the string is broken into bytes, then the
               bits of each byte are broken into 8/BITS groups.  Bits of a
               byte are numbered in a little-endian-ish way, as in 0x01, 0x02,
               0x04, 0x08, 0x10, 0x20, 0x40, 0x80.  For example, breaking the
               single input byte "chr(0x36)" into two groups gives a list
               "(0x6, 0x3)"; breaking it into 4 groups gives "(0x2, 0x1, 0x3,
               0x0)".

               "vec" may also be assigned to, in which case parentheses are
               needed to give the expression the correct precedence as in

                   vec($image, $max_x * $x + $y, 8) = 3;

               If the selected element is outside the string, the value 0 is
               returned.  If an element off the end of the string is written
               to, Perl will first extend the string with sufficiently many
               zero bytes.   It is an error to try to write off the beginning
               of the string (i.e. negative OFFSET).

               If the string happens to be encoded as UTF-8 internally (and
               thus has the UTF8 flag set), this is ignored by "vec", and it
               operates on the internal byte string, not the conceptual
               character string, even if you only have characters with values
               less than 256.

               Strings created with "vec" can also be manipulated with the
               logical operators "|", "&", "^", and "~".  These operators will
               assume a bit vector operation is desired when both operands are
               strings.  See "Bitwise String Operators" in perlop.

               The following code will build up an ASCII string saying
               'PerlPerlPerl'.  The comments show the string after each step.
               Note that this code works in the same way on big-endian or
               little-endian machines.

                   my $foo = '';
                   vec($foo,  0, 32) = 0x5065726C;     # 'Perl'
                   vec($foo, 93,  1) = 1;              # 'PerlPerlPer'  . "\x2c"
                   vec($foo, 94,  1) = 1;              # 'PerlPerlPerl'
                                                       # 'l' is "\x6c"

               To transform a bit vector into a string or list of 0's and 1's,
               use these:

                   $bits = unpack("b*", $vector);
                   @bits = split(//, unpack("b*", $vector));

               If you know the exact length in bits, it can be used in place
               of the "*".

               Here is an example to illustrate how the bits actually fall in
               place:

                   #!/usr/bin/perl -wl

                   print <<'EOT';
                                                     0         1         2         3
                                      unpack("V",$_) 01234567890123456789012345678901
                   ------------------------------------------------------------------
                   EOT

                   for $w (0..3) {
                       $width = 2**$w;
                       for ($shift=0; $shift < $width; ++$shift) {
                           for ($off=0; $off < 32/$width; ++$off) {
                               $str = pack("B*", "0"x32);
                               $bits = (1<<$shift);
                               vec($str, $off, $width) = $bits;
                               $res = unpack("b*",$str);
                               $val = unpack("V", $str);
                               write;
                           }
                       }
                   }

                   format STDOUT =
                   vec($_,@#,@#) = @<< == @######### @>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
                   $off, $width, $bits, $val, $res
                   .
                   __END__

               Regardless of the machine architecture on which it is run, the
               above example should print the following table:

                                                     0         1         2         3
                                      unpack("V",$_) 01234567890123456789012345678901
                   ------------------------------------------------------------------
                   vec($_, 0, 1) = 1   ==          1 10000000000000000000000000000000
                   vec($_, 1, 1) = 1   ==          2 01000000000000000000000000000000
                   vec($_, 2, 1) = 1   ==          4 00100000000000000000000000000000
                   vec($_, 3, 1) = 1   ==          8 00010000000000000000000000000000
                   vec($_,16, 1) = 1   ==      65536 00000000000000001000000000000000
                   vec($_,17, 1) = 1   ==     131072 00000000000000000100000000000000
                   vec($_,18, 1) = 1   ==     262144 00000000000000000010000000000000
                   vec($_,19, 1) = 1   ==     524288 00000000000000000001000000000000
                   vec($_,20, 1) = 1   ==    1048576 00000000000000000000100000000000
                   vec($_,21, 1) = 1   ==    2097152 00000000000000000000010000000000
                   vec($_,22, 1) = 1   ==    4194304 00000000000000000000001000000000
                   vec($_,23, 1) = 1   ==    8388608 00000000000000000000000100000000
                   vec($_,24, 1) = 1   ==   16777216 00000000000000000000000010000000
                   vec($_,25, 1) = 1   ==   33554432 00000000000000000000000001000000
                   vec($_,26, 1) = 1   ==   67108864 00000000000000000000000000100000
                   vec($_,27, 1) = 1   ==  134217728 00000000000000000000000000010000
                   vec($_,28, 1) = 1   ==  268435456 00000000000000000000000000001000
                   vec($_,29, 1) = 1   ==  536870912 00000000000000000000000000000100
                   vec($_,30, 1) = 1   == 1073741824 00000000000000000000000000000010
                   vec($_,31, 1) = 1   == 2147483648 00000000000000000000000000000001
                   vec($_, 0, 2) = 1   ==          1 10000000000000000000000000000000
                   vec($_, 1, 2) = 1   ==          4 00100000000000000000000000000000
                   vec($_, 2, 2) = 1   ==         16 00001000000000000000000000000000
                   vec($_, 3, 2) = 1   ==         64 00000010000000000000000000000000
                   vec($_, 4, 2) = 1   ==        256 00000000100000000000000000000000
                   vec($_, 5, 2) = 1   ==       1024 00000000001000000000000000000000
                   vec($_, 6, 2) = 1   ==       4096 00000000000010000000000000000000
                   vec($_, 7, 2) = 1   ==      16384 00000000000000100000000000000000
                   vec($_, 8, 2) = 1   ==      65536 00000000000000001000000000000000
                   vec($_, 9, 2) = 1   ==     262144 00000000000000000010000000000000
                   vec($_,10, 2) = 1   ==    1048576 00000000000000000000100000000000
                   vec($_,11, 2) = 1   ==    4194304 00000000000000000000001000000000
                   vec($_,12, 2) = 1   ==   16777216 00000000000000000000000010000000
                   vec($_,13, 2) = 1   ==   67108864 00000000000000000000000000100000
                   vec($_,14, 2) = 1   ==  268435456 00000000000000000000000000001000
                   vec($_,15, 2) = 1   == 1073741824 00000000000000000000000000000010
                   vec($_, 0, 2) = 2   ==          2 01000000000000000000000000000000
                   vec($_, 1, 2) = 2   ==          8 00010000000000000000000000000000
                   vec($_, 2, 2) = 2   ==         32 00000100000000000000000000000000
                   vec($_, 3, 2) = 2   ==        128 00000001000000000000000000000000
                   vec($_, 4, 2) = 2   ==        512 00000000010000000000000000000000
                   vec($_, 5, 2) = 2   ==       2048 00000000000100000000000000000000
                   vec($_, 6, 2) = 2   ==       8192 00000000000001000000000000000000
                   vec($_, 7, 2) = 2   ==      32768 00000000000000010000000000000000
                   vec($_, 8, 2) = 2   ==     131072 00000000000000000100000000000000
                   vec($_, 9, 2) = 2   ==     524288 00000000000000000001000000000000
                   vec($_,10, 2) = 2   ==    2097152 00000000000000000000010000000000
                   vec($_,11, 2) = 2   ==    8388608 00000000000000000000000100000000
                   vec($_,12, 2) = 2   ==   33554432 00000000000000000000000001000000
                   vec($_,13, 2) = 2   ==  134217728 00000000000000000000000000010000
                   vec($_,14, 2) = 2   ==  536870912 00000000000000000000000000000100
                   vec($_,15, 2) = 2   == 2147483648 00000000000000000000000000000001
                   vec($_, 0, 4) = 1   ==          1 10000000000000000000000000000000
                   vec($_, 1, 4) = 1   ==         16 00001000000000000000000000000000
                   vec($_, 2, 4) = 1   ==        256 00000000100000000000000000000000
                   vec($_, 3, 4) = 1   ==       4096 00000000000010000000000000000000
                   vec($_, 4, 4) = 1   ==      65536 00000000000000001000000000000000
                   vec($_, 5, 4) = 1   ==    1048576 00000000000000000000100000000000
                   vec($_, 2, 4) = 4   ==       1024 00000000001000000000000000000000
                   vec($_, 3, 4) = 4   ==      16384 00000000000000100000000000000000
                   vec($_, 4, 4) = 4   ==     262144 00000000000000000010000000000000
                   vec($_, 5, 4) = 4   ==    4194304 00000000000000000000001000000000
                   vec($_, 6, 4) = 4   ==   67108864 00000000000000000000000000100000
                   vec($_, 7, 4) = 4   == 1073741824 00000000000000000000000000000010
                   vec($_, 0, 4) = 8   ==          8 00010000000000000000000000000000
                   vec($_, 1, 4) = 8   ==        128 00000001000000000000000000000000
                   vec($_, 2, 4) = 8   ==       2048 00000000000100000000000000000000
                   vec($_, 3, 4) = 8   ==      32768 00000000000000010000000000000000
                   vec($_, 4, 4) = 8   ==     524288 00000000000000000001000000000000
                   vec($_, 5, 4) = 8   ==    8388608 00000000000000000000000100000000
                   vec($_, 6, 4) = 8   ==  134217728 00000000000000000000000000010000
                   vec($_, 7, 4) = 8   == 2147483648 00000000000000000000000000000001
                   vec($_, 0, 8) = 1   ==          1 10000000000000000000000000000000
                   vec($_, 1, 8) = 1   ==        256 00000000100000000000000000000000
                   vec($_, 2, 8) = 1   ==      65536 00000000000000001000000000000000
                   vec($_, 3, 8) = 1   ==   16777216 00000000000000000000000010000000
                   vec($_, 0, 8) = 2   ==          2 01000000000000000000000000000000
                   vec($_, 1, 8) = 2   ==        512 00000000010000000000000000000000
                   vec($_, 2, 8) = 2   ==     131072 00000000000000000100000000000000
                   vec($_, 3, 8) = 2   ==   33554432 00000000000000000000000001000000
                   vec($_, 0, 8) = 4   ==          4 00100000000000000000000000000000
                   vec($_, 1, 8) = 4   ==       1024 00000000001000000000000000000000
                   vec($_, 2, 8) = 4   ==     262144 00000000000000000010000000000000
                   vec($_, 3, 8) = 4   ==   67108864 00000000000000000000000000100000
                   vec($_, 0, 8) = 8   ==          8 00010000000000000000000000000000
                   vec($_, 1, 8) = 8   ==       2048 00000000000100000000000000000000
                   vec($_, 2, 8) = 8   ==     524288 00000000000000000001000000000000
                   vec($_, 3, 8) = 8   ==  134217728 00000000000000000000000000010000
                   vec($_, 0, 8) = 16  ==         16 00001000000000000000000000000000
                   vec($_, 1, 8) = 16  ==       4096 00000000000010000000000000000000
                   vec($_, 2, 8) = 16  ==    1048576 00000000000000000000100000000000
                   vec($_, 3, 8) = 16  ==  268435456 00000000000000000000000000001000
                   vec($_, 0, 8) = 32  ==         32 00000100000000000000000000000000
                   vec($_, 1, 8) = 32  ==       8192 00000000000001000000000000000000
                   vec($_, 2, 8) = 32  ==    2097152 00000000000000000000010000000000
                   vec($_, 3, 8) = 32  ==  536870912 00000000000000000000000000000100
                   vec($_, 0, 8) = 64  ==         64 00000010000000000000000000000000
                   vec($_, 1, 8) = 64  ==      16384 00000000000000100000000000000000
                   vec($_, 2, 8) = 64  ==    4194304 00000000000000000000001000000000
                   vec($_, 3, 8) = 64  == 1073741824 00000000000000000000000000000010
                   vec($_, 0, 8) = 128 ==        128 00000001000000000000000000000000
                   vec($_, 1, 8) = 128 ==      32768 00000000000000010000000000000000
                   vec($_, 2, 8) = 128 ==    8388608 00000000000000000000000100000000
                   vec($_, 3, 8) = 128 == 2147483648 00000000000000000000000000000001

       wait    Behaves like the wait(2) system call on your system: it waits
               for a child process to terminate and returns the pid of the
               deceased process, or "-1" if there are no child processes.  The
               status is returned in $?  and "${^CHILD_ERROR_NATIVE}".  Note
               that a return value of "-1" could mean that child processes are
               being automatically reaped, as described in perlipc.


               then you can do a non-blocking wait for all pending zombie
               processes.  Non-blocking wait is available on machines
               supporting either the waitpid(2) or wait4(2) system calls.
               However, waiting for a particular pid with FLAGS of 0 is
               implemented everywhere.  (Perl emulates the system call by
               remembering the status values of processes that have exited but
               have not been harvested by the Perl script yet.)

               Note that on some systems, a return value of "-1" could mean
               that child processes are being automatically reaped.  See
               perlipc for details, and for other examples.

       wantarray
               Returns true if the context of the currently executing
               subroutine or "eval" is looking for a list value.  Returns
               false if the context is looking for a scalar.  Returns the
               undefined value if the context is looking for no value (void
               context).

                   return unless defined wantarray;    # don't bother doing more
                   my @a = complex_calculation();
                   return wantarray ? @a : "@a";

               "wantarray()"'s result is unspecified in the top level of a
               file, in a "BEGIN", "UNITCHECK", "CHECK", "INIT" or "END"
               block, or in a "DESTROY" method.

               This function should have been named wantlist() instead.

       warn LIST
               Prints the value of LIST to STDERR.  If the last element of
               LIST does not end in a newline, it appends the same file/line
               number text as "die" does.

               If LIST is empty and $@ already contains a value (typically
               from a previous eval) that value is used after appending
               "\t...caught" to $@.  This is useful for staying almost, but
               not entirely similar to "die".

               If $@ is empty then the string "Warning: Something's wrong" is
               used.

               No message is printed if there is a $SIG{__WARN__} handler
               installed.  It is the handler's responsibility to deal with the
               message as it sees fit (like, for instance, converting it into
               a "die").  Most handlers must therefore make arrangements to
               actually display the warnings that they are not prepared to
               deal with, by calling "warn" again in the handler.  Note that
               this is quite safe and will not produce an endless loop, since
               "__WARN__" hooks are not called from inside one.

               You will find this behavior is slightly different from that of
               $SIG{__DIE__} handlers (which don't suppress the error text,

                   # run-time warnings enabled after here
                   warn "\$foo is alive and $foo!";     # does show up

               See perlvar for details on setting %SIG entries, and for more
               examples.  See the Carp module for other kinds of warnings
               using its carp() and cluck() functions.

       write FILEHANDLE
       write EXPR
       write   Writes a formatted record (possibly multi-line) to the
               specified FILEHANDLE, using the format associated with that
               file.  By default the format for a file is the one having the
               same name as the filehandle, but the format for the current
               output channel (see the "select" function) may be set
               explicitly by assigning the name of the format to the $~
               variable.

               Top of form processing is handled automatically:  if there is
               insufficient room on the current page for the formatted record,
               the page is advanced by writing a form feed, a special top-of-
               page format is used to format the new page header, and then the
               record is written.  By default the top-of-page format is the
               name of the filehandle with "_TOP" appended, but it may be
               dynamically set to the format of your choice by assigning the
               name to the $^ variable while the filehandle is selected.  The
               number of lines remaining on the current page is in variable
               "$-", which can be set to 0 to force a new page.

               If FILEHANDLE is unspecified, output goes to the current
               default output channel, which starts out as STDOUT but may be
               changed by the "select" operator.  If the FILEHANDLE is an
               EXPR, then the expression is evaluated and the resulting string
               is used to look up the name of the FILEHANDLE at run time.  For
               more on formats, see perlform.

               Note that write is not the opposite of "read".  Unfortunately.

       y///    The transliteration operator.  Same as "tr///".  See "Quote and
               Quote-like Operators" in perlop.



perl v5.10.1                      2009-08-12                       PERLFUNC(1)
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