perlvar


DESCRIPTION
   Predefined Names
       The following names have special meaning to Perl.  Most punctuation
       names have reasonable mnemonics, or analogs in the shells.
       Nevertheless, if you wish to use long variable names, you need only say

           use English;

       at the top of your program. This aliases all the short names to the
       long names in the current package. Some even have medium names,
       generally borrowed from awk. In general, it's best to use the

           use English '-no_match_vars';

       invocation if you don't need $PREMATCH, $MATCH, or $POSTMATCH, as it
       avoids a certain performance hit with the use of regular expressions.
       See English.

       Variables that depend on the currently selected filehandle may be set
       by calling an appropriate object method on the IO::Handle object,
       although this is less efficient than using the regular built-in
       variables. (Summary lines below for this contain the word HANDLE.)
       First you must say

           use IO::Handle;

       after which you may use either

           method HANDLE EXPR

       or more safely,

           HANDLE->method(EXPR)

       Each method returns the old value of the IO::Handle attribute.  The
       methods each take an optional EXPR, which, if supplied, specifies the
       new value for the IO::Handle attribute in question.  If not supplied,
       most methods do nothing to the current value--except for autoflush(),
       which will assume a 1 for you, just to be different.

       Because loading in the IO::Handle class is an expensive operation, you
       should learn how to use the regular built-in variables.

       A few of these variables are considered "read-only".  This means that
       if you try to assign to this variable, either directly or indirectly
       through a reference, you'll raise a run-time exception.

       You should be very careful when modifying the default values of most
       special variables described in this document. In most cases you want to
       localize these variables before changing them, since if you don't, the
       change may affect other modules which rely on the default values of the
       special variables that you have changed. This is one of the correct
       ways to read the whole file at once:

       since some other module, may want to read data from some file in the
       default "line mode", so if the code we have just presented has been
       executed, the global value of $/ is now changed for any other code
       running inside the same Perl interpreter.

       Usually when a variable is localized you want to make sure that this
       change affects the shortest scope possible. So unless you are already
       inside some short "{}" block, you should create one yourself. For
       example:

           my $content = '';
           open my $fh, "<", "foo" or die $!;
           {
               local $/;
               $content = <$fh>;
           }
           close $fh;

       Here is an example of how your own code can go broken:

           for (1..5){
               nasty_break();
               print "$_ ";
           }
           sub nasty_break {
               $_ = 5;
               # do something with $_
           }

       You probably expect this code to print:

           1 2 3 4 5

       but instead you get:

           5 5 5 5 5

       Why? Because nasty_break() modifies $_ without localizing it first. The
       fix is to add local():

               local $_ = 5;

       It's easy to notice the problem in such a short example, but in more
       complicated code you are looking for trouble if you don't localize
       changes to the special variables.

       The following list is ordered by scalar variables first, then the
       arrays, then the hashes.

       $ARG
       $_      The default input and pattern-searching space.  The following
               pairs are equivalent:

               Here are the places where Perl will assume $_ even if you don't
               use it:

               o  The following functions:

                  abs, alarm, chomp, chop, chr, chroot, cos, defined, eval,
                  exp, glob, hex, int, lc, lcfirst, length, log, lstat, mkdir,
                  oct, ord, pos, print, quotemeta, readlink, readpipe, ref,
                  require, reverse (in scalar context only), rmdir, sin, split
                  (on its second argument), sqrt, stat, study, uc, ucfirst,
                  unlink, unpack.

               o  All file tests ("-f", "-d") except for "-t", which defaults
                  to STDIN.  See "-X" in perlfunc

               o  The pattern matching operations "m//", "s///" and "tr///"
                  (aka "y///") when used without an "=~" operator.

               o  The default iterator variable in a "foreach" loop if no
                  other variable is supplied.

               o  The implicit iterator variable in the grep() and map()
                  functions.

               o  The implicit variable of given().

               o  The default place to put an input record when a "<FH>"
                  operation's result is tested by itself as the sole criterion
                  of a "while" test.  Outside a "while" test, this will not
                  happen.

               As $_ is a global variable, this may lead in some cases to
               unwanted side-effects.  As of perl 5.9.1, you can now use a
               lexical version of $_ by declaring it in a file or in a block
               with "my".  Moreover, declaring "our $_" restores the global $_
               in the current scope.

               (Mnemonic: underline is understood in certain operations.)

       $a
       $b      Special package variables when using sort(), see "sort" in
               perlfunc.  Because of this specialness $a and $b don't need to
               be declared (using use vars, or our()) even when using the
               "strict 'vars'" pragma.  Don't lexicalize them with "my $a" or
               "my $b" if you want to be able to use them in the sort()
               comparison block or function.

       $<digits>
               Contains the subpattern from the corresponding set of capturing
               parentheses from the last pattern match, not counting patterns
               matched in nested blocks that have been exited already.
               (Mnemonic: like \digits.)  These variables are all read-only
               and dynamically scoped to the current BLOCK.


       ${^MATCH}
               This is similar to $& ($MATCH) except that it does not incur
               the performance penalty associated with that variable, and is
               only guaranteed to return a defined value when the pattern was
               compiled or executed with the "/p" modifier.

       $PREMATCH
       $`      The string preceding whatever was matched by the last
               successful pattern match (not counting any matches hidden
               within a BLOCK or eval enclosed by the current BLOCK).
               (Mnemonic: "`" often precedes a quoted string.)  This variable
               is read-only.

               The use of this variable anywhere in a program imposes a
               considerable performance penalty on all regular expression
               matches.  See "BUGS".

               See "@-" for a replacement.

       ${^PREMATCH}
               This is similar to "$`" ($PREMATCH) except that it does not
               incur the performance penalty associated with that variable,
               and is only guaranteed to return a defined value when the
               pattern was compiled or executed with the "/p" modifier.

       $POSTMATCH
       $'      The string following whatever was matched by the last
               successful pattern match (not counting any matches hidden
               within a BLOCK or eval() enclosed by the current BLOCK).
               (Mnemonic: "'" often follows a quoted string.)  Example:

                   local $_ = 'abcdefghi';
                   /def/;
                   print "$`:$&:$'\n";         # prints abc:def:ghi

               This variable is read-only and dynamically scoped to the
               current BLOCK.

               The use of this variable anywhere in a program imposes a
               considerable performance penalty on all regular expression
               matches.  See "BUGS".

               See "@-" for a replacement.

       ${^POSTMATCH}
               This is similar to "$'" ($POSTMATCH) except that it does not
               incur the performance penalty associated with that variable,
               and is only guaranteed to return a defined value when the
               pattern was compiled or executed with the "/p" modifier.

       $LAST_PAREN_MATCH
       $+      The text matched by the last bracket of the last successful
               search pattern.  This is useful if you don't know which one of

               This is primarily used inside "(?{...})" blocks for examining
               text recently matched. For example, to effectively capture text
               to a variable (in addition to $1, $2, etc.), replace "(...)"
               with

                    (?:(...)(?{ $var = $^N }))

               By setting and then using $var in this way relieves you from
               having to worry about exactly which numbered set of parentheses
               they are.

               This variable is dynamically scoped to the current BLOCK.

       @LAST_MATCH_END
       @+      This array holds the offsets of the ends of the last successful
               submatches in the currently active dynamic scope.  $+[0] is the
               offset into the string of the end of the entire match.  This is
               the same value as what the "pos" function returns when called
               on the variable that was matched against.  The nth element of
               this array holds the offset of the nth submatch, so $+[1] is
               the offset past where $1 ends, $+[2] the offset past where $2
               ends, and so on.  You can use $#+ to determine how many
               subgroups were in the last successful match.  See the examples
               given for the "@-" variable.

       %LAST_PAREN_MATCH
       %+      Similar to "@+", the "%+" hash allows access to the named
               capture buffers, should they exist, in the last successful
               match in the currently active dynamic scope.

               For example, $+{foo} is equivalent to $1 after the following
               match:

                 'foo' =~ /(?<foo>foo)/;

               The keys of the "%+" hash list only the names of buffers that
               have captured (and that are thus associated to defined values).

               The underlying behaviour of "%+" is provided by the
               Tie::Hash::NamedCapture module.

               Note: "%-" and "%+" are tied views into a common internal hash
               associated with the last successful regular expression.
               Therefore mixing iterative access to them via "each" may have
               unpredictable results.  Likewise, if the last successful match
               changes, then the results may be surprising.

       HANDLE->input_line_number(EXPR)
       $INPUT_LINE_NUMBER
       $NR
       $.      Current line number for the last filehandle accessed.

               Each filehandle in Perl counts the number of lines that have
               $. is reset when the filehandle is closed, but not when an open
               filehandle is reopened without an intervening close().  For
               more details, see "I/O Operators" in perlop.  Because "<>"
               never does an explicit close, line numbers increase across ARGV
               files (but see examples in "eof" in perlfunc).

               You can also use "HANDLE->input_line_number(EXPR)" to access
               the line counter for a given filehandle without having to worry
               about which handle you last accessed.

               (Mnemonic: many programs use "." to mean the current line
               number.)

       IO::Handle->input_record_separator(EXPR)
       $INPUT_RECORD_SEPARATOR
       $RS
       $/      The input record separator, newline by default.  This
               influences Perl's idea of what a "line" is.  Works like awk's
               RS variable, including treating empty lines as a terminator if
               set to the null string.  (An empty line cannot contain any
               spaces or tabs.)  You may set it to a multi-character string to
               match a multi-character terminator, or to "undef" to read
               through the end of file.  Setting it to "\n\n" means something
               slightly different than setting to "", if the file contains
               consecutive empty lines.  Setting to "" will treat two or more
               consecutive empty lines as a single empty line.  Setting to
               "\n\n" will blindly assume that the next input character
               belongs to the next paragraph, even if it's a newline.
               (Mnemonic: / delimits line boundaries when quoting poetry.)

                   local $/;           # enable "slurp" mode
                   local $_ = <FH>;    # whole file now here
                   s/\n[ \t]+/ /g;

               Remember: the value of $/ is a string, not a regex.  awk has to
               be better for something. :-)

               Setting $/ to a reference to an integer, scalar containing an
               integer, or scalar that's convertible to an integer will
               attempt to read records instead of lines, with the maximum
               record size being the referenced integer.  So this:

                   local $/ = \32768; # or \"32768", or \$var_containing_32768
                   open my $fh, "<", $myfile or die $!;
                   local $_ = <$fh>;

               will read a record of no more than 32768 bytes from FILE.  If
               you're not reading from a record-oriented file (or your OS
               doesn't have record-oriented files), then you'll likely get a
               full chunk of data with every read.  If a record is larger than
               the record size you've set, you'll get the record back in
               pieces.  Trying to set the record size to zero or less will
               cause reading in the (rest of the) whole file.

               write or print on the currently selected output channel.
               Default is 0 (regardless of whether the channel is really
               buffered by the system or not; $| tells you only whether you've
               asked Perl explicitly to flush after each write).  STDOUT will
               typically be line buffered if output is to the terminal and
               block buffered otherwise.  Setting this variable is useful
               primarily when you are outputting to a pipe or socket, such as
               when you are running a Perl program under rsh and want to see
               the output as it's happening.  This has no effect on input
               buffering.  See "getc" in perlfunc for that.  See "select" in
               perldoc on how to select the output channel.  See also
               IO::Handle. (Mnemonic: when you want your pipes to be piping
               hot.)

       IO::Handle->output_field_separator EXPR
       $OUTPUT_FIELD_SEPARATOR
       $OFS
       $,      The output field separator for the print operator.  If defined,
               this value is printed between each of print's arguments.
               Default is "undef".  (Mnemonic: what is printed when there is a
               "," in your print statement.)

       IO::Handle->output_record_separator EXPR
       $OUTPUT_RECORD_SEPARATOR
       $ORS
       $\      The output record separator for the print operator.  If
               defined, this value is printed after the last of print's
               arguments.  Default is "undef".  (Mnemonic: you set "$\"
               instead of adding "\n" at the end of the print.  Also, it's
               just like $/, but it's what you get "back" from Perl.)

       $LIST_SEPARATOR
       $"      This is like $, except that it applies to array and slice
               values interpolated into a double-quoted string (or similar
               interpreted string).  Default is a space.  (Mnemonic: obvious,
               I think.)

       $SUBSCRIPT_SEPARATOR
       $SUBSEP
       $;      The subscript separator for multidimensional array emulation.
               If you refer to a hash element as

                   $foo{$a,$b,$c}

               it really means

                   $foo{join($;, $a, $b, $c)}

               But don't put

                   @foo{$a,$b,$c}      # a slice--note the @

               which means

       $FORMAT_PAGE_NUMBER
       $%      The current page number of the currently selected output
               channel.  Used with formats.  (Mnemonic: % is page number in
               nroff.)

       HANDLE->format_lines_per_page(EXPR)
       $FORMAT_LINES_PER_PAGE
       $=      The current page length (printable lines) of the currently
               selected output channel.  Default is 60.  Used with formats.
               (Mnemonic: = has horizontal lines.)

       HANDLE->format_lines_left(EXPR)
       $FORMAT_LINES_LEFT
       $-      The number of lines left on the page of the currently selected
               output channel.  Used with formats.  (Mnemonic: lines_on_page -
               lines_printed.)

       @LAST_MATCH_START
       @-      $-[0] is the offset of the start of the last successful match.
               "$-["n"]" is the offset of the start of the substring matched
               by n-th subpattern, or undef if the subpattern did not match.

               Thus after a match against $_, $& coincides with "substr $_,
               $-[0], $+[0] - $-[0]".  Similarly, $n coincides with "substr
               $_, $-[n], $+[n] - $-[n]" if "$-[n]" is defined, and $+
               coincides with "substr $_, $-[$#-], $+[$#-] - $-[$#-]".  One
               can use "$#-" to find the last matched subgroup in the last
               successful match.  Contrast with $#+, the number of subgroups
               in the regular expression.  Compare with "@+".

               This array holds the offsets of the beginnings of the last
               successful submatches in the currently active dynamic scope.
               "$-[0]" is the offset into the string of the beginning of the
               entire match.  The nth element of this array holds the offset
               of the nth submatch, so "$-[1]" is the offset where $1 begins,
               "$-[2]" the offset where $2 begins, and so on.

               After a match against some variable $var:

               "$`" is the same as "substr($var, 0, $-[0])"
               $& is the same as "substr($var, $-[0], $+[0] - $-[0])"
               "$'" is the same as "substr($var, $+[0])"
               $1 is the same as "substr($var, $-[1], $+[1] - $-[1])"
               $2 is the same as "substr($var, $-[2], $+[2] - $-[2])"
               $3 is the same as "substr($var, $-[3], $+[3] - $-[3])"
       %-      Similar to "%+", this variable allows access to the named
               capture buffers in the last successful match in the currently
               active dynamic scope. To each capture buffer name found in the
               regular expression, it associates a reference to an array
               containing the list of values captured by all buffers with that
               name (should there be several of them), in the order where they
               appear.

               Here's an example:
               would print out:

                   $-{A}[0] : '1'
                   $-{A}[1] : '3'
                   $-{B}[0] : '2'
                   $-{B}[1] : '4'

               The keys of the "%-" hash correspond to all buffer names found
               in the regular expression.

               The behaviour of "%-" is implemented via the
               Tie::Hash::NamedCapture module.

               Note: "%-" and "%+" are tied views into a common internal hash
               associated with the last successful regular expression.
               Therefore mixing iterative access to them via "each" may have
               unpredictable results.  Likewise, if the last successful match
               changes, then the results may be surprising.

       HANDLE->format_name(EXPR)
       $FORMAT_NAME
       $~      The name of the current report format for the currently
               selected output channel.  Default is the name of the
               filehandle.  (Mnemonic: brother to $^.)

       HANDLE->format_top_name(EXPR)
       $FORMAT_TOP_NAME
       $^      The name of the current top-of-page format for the currently
               selected output channel.  Default is the name of the filehandle
               with _TOP appended.  (Mnemonic: points to top of page.)

       IO::Handle->format_line_break_characters EXPR
       $FORMAT_LINE_BREAK_CHARACTERS
       $:      The current set of characters after which a string may be
               broken to fill continuation fields (starting with ^) in a
               format.  Default is " \n-", to break on whitespace or hyphens.
               (Mnemonic: a "colon" in poetry is a part of a line.)

       IO::Handle->format_formfeed EXPR
       $FORMAT_FORMFEED
       $^L     What formats output as a form feed.  Default is \f.

       $ACCUMULATOR
       $^A     The current value of the write() accumulator for format()
               lines.  A format contains formline() calls that put their
               result into $^A.  After calling its format, write() prints out
               the contents of $^A and empties.  So you never really see the
               contents of $^A unless you call formline() yourself and then
               look at it.  See perlform and "formline()" in perlfunc.

       $CHILD_ERROR
       $?      The status returned by the last pipe close, backtick ("``")
               command, successful call to wait() or waitpid(), or from the
               system() operator.  This is just the 16-bit status word

               Inside an "END" subroutine $? contains the value that is going
               to be given to "exit()".  You can modify $? in an "END"
               subroutine to change the exit status of your program.  For
               example:

                   END {
                       $? = 1 if $? == 255;  # die would make it 255
                   }

               Under VMS, the pragma "use vmsish 'status'" makes $? reflect
               the actual VMS exit status, instead of the default emulation of
               POSIX status; see "$?" in perlvms for details.

               Also see "Error Indicators".

       ${^CHILD_ERROR_NATIVE}
               The native status returned by the last pipe close, backtick
               ("``") command, successful call to wait() or waitpid(), or from
               the system() operator.  On POSIX-like systems this value can be
               decoded with the WIFEXITED, WEXITSTATUS, WIFSIGNALED, WTERMSIG,
               WIFSTOPPED, WSTOPSIG and WIFCONTINUED functions provided by the
               POSIX module.

               Under VMS this reflects the actual VMS exit status; i.e. it is
               the same as $? when the pragma "use vmsish 'status'" is in
               effect.

       ${^ENCODING}
               The object reference to the Encode object that is used to
               convert the source code to Unicode.  Thanks to this variable
               your perl script does not have to be written in UTF-8.  Default
               is undef.  The direct manipulation of this variable is highly
               discouraged.

       $OS_ERROR
       $ERRNO
       $!      If used numerically, yields the current value of the C "errno"
               variable, or in other words, if a system or library call fails,
               it sets this variable.  This means that the value of $! is
               meaningful only immediately after a failure:

                   if (open my $fh, "<", $filename) {
                       # Here $! is meaningless.
                       ...
                   } else {
                       # ONLY here is $! meaningful.
                       ...
                       # Already here $! might be meaningless.
                   }
                   # Since here we might have either success or failure,
                   # here $! is meaningless.

               In the above meaningless stands for anything: zero, non-zero,

       %ERRNO
       %!      Each element of "%!" has a true value only if $! is set to that
               value.  For example, $!{ENOENT} is true if and only if the
               current value of $! is "ENOENT"; that is, if the most recent
               error was "No such file or directory" (or its moral equivalent:
               not all operating systems give that exact error, and certainly
               not all languages).  To check if a particular key is meaningful
               on your system, use "exists $!{the_key}"; for a list of legal
               keys, use "keys %!".  See Errno for more information, and also
               see above for the validity of $!.

       $EXTENDED_OS_ERROR
       $^E     Error information specific to the current operating system.  At
               the moment, this differs from $! under only VMS, OS/2, and
               Win32 (and for MacPerl).  On all other platforms, $^E is always
               just the same as $!.

               Under VMS, $^E provides the VMS status value from the last
               system error.  This is more specific information about the last
               system error than that provided by $!.  This is particularly
               important when $! is set to EVMSERR.

               Under OS/2, $^E is set to the error code of the last call to
               OS/2 API either via CRT, or directly from perl.

               Under Win32, $^E always returns the last error information
               reported by the Win32 call "GetLastError()" which describes the
               last error from within the Win32 API.  Most Win32-specific code
               will report errors via $^E.  ANSI C and Unix-like calls set
               "errno" and so most portable Perl code will report errors via
               $!.

               Caveats mentioned in the description of $! generally apply to
               $^E, also.  (Mnemonic: Extra error explanation.)

               Also see "Error Indicators".

       $EVAL_ERROR
       $@      The Perl syntax error message from the last eval() operator.
               If $@ is the null string, the last eval() parsed and executed
               correctly (although the operations you invoked may have failed
               in the normal fashion).  (Mnemonic: Where was the syntax error
               "at"?)

               Warning messages are not collected in this variable.  You can,
               however, set up a routine to process warnings by setting
               $SIG{__WARN__} as described below.

               Also see "Error Indicators".

       $PROCESS_ID
       $PID
       $$      The process number of the Perl running this script.  You should
               consider this variable read-only, although it will be altered
               from, if you're running setuid.)  You can change both the real
               uid and the effective uid at the same time by using
               POSIX::setuid().  Since changes to $< require a system call,
               check $! after a change attempt to detect any possible errors.

       $EFFECTIVE_USER_ID
       $EUID
       $>      The effective uid of this process.  Example:

                   $< = $>;            # set real to effective uid
                   ($<,$>) = ($>,$<);  # swap real and effective uid

               You can change both the effective uid and the real uid at the
               same time by using POSIX::setuid().  Changes to $> require a
               check to $!  to detect any possible errors after an attempted
               change.

               (Mnemonic: it's the uid you went to, if you're running setuid.)
               $< and $> can be swapped only on machines supporting
               setreuid().

       $REAL_GROUP_ID
       $GID
       $(      The real gid of this process.  If you are on a machine that
               supports membership in multiple groups simultaneously, gives a
               space separated list of groups you are in.  The first number is
               the one returned by getgid(), and the subsequent ones by
               getgroups(), one of which may be the same as the first number.

               However, a value assigned to $( must be a single number used to
               set the real gid.  So the value given by $( should not be
               assigned back to $( without being forced numeric, such as by
               adding zero. Note that this is different to the effective gid
               ($)) which does take a list.

               You can change both the real gid and the effective gid at the
               same time by using POSIX::setgid().  Changes to $( require a
               check to $!  to detect any possible errors after an attempted
               change.

               (Mnemonic: parentheses are used to group things.  The real gid
               is the group you left, if you're running setgid.)

       $EFFECTIVE_GROUP_ID
       $EGID
       $)      The effective gid of this process.  If you are on a machine
               that supports membership in multiple groups simultaneously,
               gives a space separated list of groups you are in.  The first
               number is the one returned by getegid(), and the subsequent
               ones by getgroups(), one of which may be the same as the first
               number.

               Similarly, a value assigned to $) must also be a space-
               separated list of numbers.  The first number sets the effective
               setgid.)

               $<, $>, $( and $) can be set only on machines that support the
               corresponding set[re][ug]id() routine.  $( and $) can be
               swapped only on machines supporting setregid().

       $PROGRAM_NAME
       $0      Contains the name of the program being executed.

               On some (read: not all) operating systems assigning to $0
               modifies the argument area that the "ps" program sees.  On some
               platforms you may have to use special "ps" options or a
               different "ps" to see the changes.  Modifying the $0 is more
               useful as a way of indicating the current program state than it
               is for hiding the program you're running.  (Mnemonic: same as
               sh and ksh.)

               Note that there are platform specific limitations on the
               maximum length of $0.  In the most extreme case it may be
               limited to the space occupied by the original $0.

               In some platforms there may be arbitrary amount of padding, for
               example space characters, after the modified name as shown by
               "ps".  In some platforms this padding may extend all the way to
               the original length of the argument area, no matter what you do
               (this is the case for example with Linux 2.2).

               Note for BSD users: setting $0 does not completely remove
               "perl" from the ps(1) output.  For example, setting $0 to
               "foobar" may result in "perl: foobar (perl)" (whether both the
               "perl: " prefix and the " (perl)" suffix are shown depends on
               your exact BSD variant and version).  This is an operating
               system feature, Perl cannot help it.

               In multithreaded scripts Perl coordinates the threads so that
               any thread may modify its copy of the $0 and the change becomes
               visible to ps(1) (assuming the operating system plays along).
               Note that the view of $0 the other threads have will not change
               since they have their own copies of it.

               If the program has been given to perl via the switches "-e" or
               "-E", $0 will contain the string "-e".

       $[      The index of the first element in an array, and of the first
               character in a substring.  Default is 0, but you could
               theoretically set it to 1 to make Perl behave more like awk (or
               Fortran) when subscripting and when evaluating the index() and
               substr() functions.  (Mnemonic: [ begins subscripts.)

               As of release 5 of Perl, assignment to $[ is treated as a
               compiler directive, and cannot influence the behavior of any
               other file.  (That's why you can only assign compile-time
               constants to it.)  Its use is highly discouraged.


               See also the documentation of "use VERSION" and "require
               VERSION" for a convenient way to fail if the running Perl
               interpreter is too old.

               The floating point representation can sometimes lead to
               inaccurate numeric comparisons.  See $^V for a more modern
               representation of the Perl version that allows accurate string
               comparisons.

       $COMPILING
       $^C     The current value of the flag associated with the -c switch.
               Mainly of use with -MO=... to allow code to alter its behavior
               when being compiled, such as for example to AUTOLOAD at compile
               time rather than normal, deferred loading.  Setting "$^C = 1"
               is similar to calling "B::minus_c".

       $DEBUGGING
       $^D     The current value of the debugging flags.  (Mnemonic: value of
               -D switch.) May be read or set. Like its command-line
               equivalent, you can use numeric or symbolic values, eg "$^D =
               10" or "$^D = "st"".

       ${^RE_DEBUG_FLAGS}
               The current value of the regex debugging flags. Set to 0 for no
               debug output even when the re 'debug' module is loaded. See re
               for details.

       ${^RE_TRIE_MAXBUF}
               Controls how certain regex optimisations are applied and how
               much memory they utilize. This value by default is 65536 which
               corresponds to a 512kB temporary cache. Set this to a higher
               value to trade memory for speed when matching large
               alternations. Set it to a lower value if you want the
               optimisations to be as conservative of memory as possible but
               still occur, and set it to a negative value to prevent the
               optimisation and conserve the most memory.  Under normal
               situations this variable should be of no interest to you.

       $SYSTEM_FD_MAX
       $^F     The maximum system file descriptor, ordinarily 2.  System file
               descriptors are passed to exec()ed processes, while higher file
               descriptors are not.  Also, during an open(), system file
               descriptors are preserved even if the open() fails.  (Ordinary
               file descriptors are closed before the open() is attempted.)
               The close-on-exec status of a file descriptor will be decided
               according to the value of $^F when the corresponding file,
               pipe, or socket was opened, not the time of the exec().

       $^H     WARNING: This variable is strictly for internal use only.  Its
               availability, behavior, and contents are subject to change
               without notice.

               This variable contains compile-time hints for the Perl

               This behavior provides the semantic of lexical scoping, and is
               used in, for instance, the "use strict" pragma.

               The contents should be an integer; different bits of it are
               used for different pragmatic flags.  Here's an example:

                   sub add_100 { $^H |= 0x100 }

                   sub foo {
                       BEGIN { add_100() }
                       bar->baz($boon);
                   }

               Consider what happens during execution of the BEGIN block.  At
               this point the BEGIN block has already been compiled, but the
               body of foo() is still being compiled.  The new value of $^H
               will therefore be visible only while the body of foo() is being
               compiled.

               Substitution of the above BEGIN block with:

                   BEGIN { require strict; strict->import('vars') }

               demonstrates how "use strict 'vars'" is implemented.  Here's a
               conditional version of the same lexical pragma:

                   BEGIN { require strict; strict->import('vars') if $condition }

       %^H     The %^H hash provides the same scoping semantic as $^H.  This
               makes it useful for implementation of lexically scoped pragmas.
               See perlpragma.

       $INPLACE_EDIT
       $^I     The current value of the inplace-edit extension.  Use "undef"
               to disable inplace editing.  (Mnemonic: value of -i switch.)

       $^M     By default, running out of memory is an untrappable, fatal
               error.  However, if suitably built, Perl can use the contents
               of $^M as an emergency memory pool after die()ing.  Suppose
               that your Perl were compiled with "-DPERL_EMERGENCY_SBRK" and
               used Perl's malloc.  Then

                   $^M = 'a' x (1 << 16);

               would allocate a 64K buffer for use in an emergency.  See the
               INSTALL file in the Perl distribution for information on how to
               add custom C compilation flags when compiling perl.  To
               discourage casual use of this advanced feature, there is no
               English long name for this variable.

       $OSNAME
       $^O     The name of the operating system under which this copy of Perl
               was built, as determined during the configuration process.  The
               layers, the second part describes the output layers.

       $PERLDB
       $^P     The internal variable for debugging support.  The meanings of
               the various bits are subject to change, but currently indicate:

               0x01  Debug subroutine enter/exit.

               0x02  Line-by-line debugging. Causes DB::DB() subroutine to be
                     called for each statement executed. Also causes saving
                     source code lines (like 0x400).

               0x04  Switch off optimizations.

               0x08  Preserve more data for future interactive inspections.

               0x10  Keep info about source lines on which a subroutine is
                     defined.

               0x20  Start with single-step on.

               0x40  Use subroutine address instead of name when reporting.

               0x80  Report "goto &subroutine" as well.

               0x100 Provide informative "file" names for evals based on the
                     place they were compiled.

               0x200 Provide informative names to anonymous subroutines based
                     on the place they were compiled.

               0x400 Save source code lines into "@{"_<$filename"}".

               Some bits may be relevant at compile-time only, some at run-
               time only.  This is a new mechanism and the details may change.
               See also perldebguts.

       $LAST_REGEXP_CODE_RESULT
       $^R     The result of evaluation of the last successful "(?{ code })"
               regular expression assertion (see perlre).  May be written to.

       $EXCEPTIONS_BEING_CAUGHT
       $^S     Current state of the interpreter.

                   $^S         State
                   ---------   -------------------
                   undef       Parsing module/eval
                   true (1)    Executing an eval
                   false (0)   Otherwise

               The first state may happen in $SIG{__DIE__} and $SIG{__WARN__}
               handlers.

       $BASETIME
               the possible values. This variable is set during Perl startup
               and is thereafter read-only.

       ${^UTF8CACHE}
               This variable controls the state of the internal UTF-8 offset
               caching code.  1 for on (the default), 0 for off, -1 to debug
               the caching code by checking all its results against linear
               scans, and panicking on any discrepancy.

       ${^UTF8LOCALE}
               This variable indicates whether an UTF-8 locale was detected by
               perl at startup. This information is used by perl when it's in
               adjust-utf8ness-to-locale mode (as when run with the "-CL"
               command-line switch); see perlrun for more info on this.

       $PERL_VERSION
       $^V     The revision, version, and subversion of the Perl interpreter,
               represented as a "version" object.

               This variable first appeared in perl 5.6.0; earlier versions of
               perl will see an undefined value. Before perl 5.10.0 $^V was
               represented as a v-string.

               $^V can be used to determine whether the Perl interpreter
               executing a script is in the right range of versions.
               (Mnemonic: use ^V for Version Control.)  Example:

                   warn "Hashes not randomized!\n" if !$^V or $^V lt v5.8.1

               To convert $^V into its string representation use sprintf()'s
               "%vd" conversion:

                   printf "version is v%vd\n", $^V;  # Perl's version

               See the documentation of "use VERSION" and "require VERSION"
               for a convenient way to fail if the running Perl interpreter is
               too old.

               See also $] for an older representation of the Perl version.

       $WARNING
       $^W     The current value of the warning switch, initially true if -w
               was used, false otherwise, but directly modifiable.  (Mnemonic:
               related to the -w switch.)  See also warnings.

       ${^WARNING_BITS}
               The current set of warning checks enabled by the "use warnings"
               pragma.  See the documentation of "warnings" for more details.

       ${^WIN32_SLOPPY_STAT}
               If this variable is set to a true value, then stat() on Windows
               will not try to open the file. This means that the link count
               cannot be determined and file attributes may be out of date if
               additional hardlinks to the file exist. On the other hand, not
               Depending on the host operating system, the value of $^X may be
               a relative or absolute pathname of the perl program file, or
               may be the string used to invoke perl but not the pathname of
               the perl program file.  Also, most operating systems permit
               invoking programs that are not in the PATH environment
               variable, so there is no guarantee that the value of $^X is in
               PATH.  For VMS, the value may or may not include a version
               number.

               You usually can use the value of $^X to re-invoke an
               independent copy of the same perl that is currently running,
               e.g.,

                 @first_run = `$^X -le "print int rand 100 for 1..100"`;

               But recall that not all operating systems support forking or
               capturing of the output of commands, so this complex statement
               may not be portable.

               It is not safe to use the value of $^X as a path name of a
               file, as some operating systems that have a mandatory suffix on
               executable files do not require use of the suffix when invoking
               a command.  To convert the value of $^X to a path name, use the
               following statements:

                 # Build up a set of file names (not command names).
                 use Config;
                 $this_perl = $^X;
                 if ($^O ne 'VMS')
                    {$this_perl .= $Config{_exe}
                         unless $this_perl =~ m/$Config{_exe}$/i;}

               Because many operating systems permit anyone with read access
               to the Perl program file to make a copy of it, patch the copy,
               and then execute the copy, the security-conscious Perl
               programmer should take care to invoke the installed copy of
               perl, not the copy referenced by $^X.  The following statements
               accomplish this goal, and produce a pathname that can be
               invoked as a command or referenced as a file.

                 use Config;
                 $secure_perl_path = $Config{perlpath};
                 if ($^O ne 'VMS')
                    {$secure_perl_path .= $Config{_exe}
                         unless $secure_perl_path =~ m/$Config{_exe}$/i;}

       ARGV    The special filehandle that iterates over command-line
               filenames in @ARGV. Usually written as the null filehandle in
               the angle operator "<>". Note that currently "ARGV" only has
               its magical effect within the "<>" operator; elsewhere it is
               just a plain filehandle corresponding to the last file opened
               by "<>". In particular, passing "\*ARGV" as a parameter to a
               function that expects a filehandle may not cause your function
               to automatically read the contents of all the files in @ARGV.

       @F      The array @F contains the fields of each line read in when
               autosplit mode is turned on.  See perlrun for the -a switch.
               This array is package-specific, and must be declared or given a
               full package name if not in package main when running under
               "strict 'vars'".

       @INC    The array @INC contains the list of places that the "do EXPR",
               "require", or "use" constructs look for their library files.
               It initially consists of the arguments to any -I command-line
               switches, followed by the default Perl library, probably
               /usr/local/lib/perl, followed by ".", to represent the current
               directory.  ("." will not be appended if taint checks are
               enabled, either by "-T" or by "-t".)  If you need to modify
               this at runtime, you should use the "use lib" pragma to get the
               machine-dependent library properly loaded also:

                   use lib '/mypath/libdir/';
                   use SomeMod;

               You can also insert hooks into the file inclusion system by
               putting Perl code directly into @INC.  Those hooks may be
               subroutine references, array references or blessed objects.
               See "require" in perlfunc for details.

       @ARG
       @_      Within a subroutine the array @_ contains the parameters passed
               to that subroutine.  See perlsub.

       %INC    The hash %INC contains entries for each filename included via
               the "do", "require", or "use" operators.  The key is the
               filename you specified (with module names converted to
               pathnames), and the value is the location of the file found.
               The "require" operator uses this hash to determine whether a
               particular file has already been included.

               If the file was loaded via a hook (e.g. a subroutine reference,
               see "require" in perlfunc for a description of these hooks),
               this hook is by default inserted into %INC in place of a
               filename.  Note, however, that the hook may have set the %INC
               entry by itself to provide some more specific info.

       %ENV
       $ENV{expr}
               The hash %ENV contains your current environment.  Setting a
               value in "ENV" changes the environment for any child processes
               you subsequently fork() off.

       %SIG
       $SIG{expr}
               The hash %SIG contains signal handlers for signals.  For
               example:

                   sub handler {       # 1st argument is signal name

               Using a value of 'IGNORE' usually has the effect of ignoring
               the signal, except for the "CHLD" signal.  See perlipc for more
               about this special case.

               Here are some other examples:

                   $SIG{"PIPE"} = "Plumber";   # assumes main::Plumber (not recommended)
                   $SIG{"PIPE"} = \&Plumber;   # just fine; assume current Plumber
                   $SIG{"PIPE"} = *Plumber;    # somewhat esoteric
                   $SIG{"PIPE"} = Plumber();   # oops, what did Plumber() return??

               Be sure not to use a bareword as the name of a signal handler,
               lest you inadvertently call it.

               If your system has the sigaction() function then signal
               handlers are installed using it.  This means you get reliable
               signal handling.

               The default delivery policy of signals changed in Perl 5.8.0
               from immediate (also known as "unsafe") to deferred, also known
               as "safe signals".  See perlipc for more information.

               Certain internal hooks can be also set using the %SIG hash.
               The routine indicated by $SIG{__WARN__} is called when a
               warning message is about to be printed.  The warning message is
               passed as the first argument.  The presence of a "__WARN__"
               hook causes the ordinary printing of warnings to "STDERR" to be
               suppressed.  You can use this to save warnings in a variable,
               or turn warnings into fatal errors, like this:

                   local $SIG{__WARN__} = sub { die $_[0] };
                   eval $proggie;

               As the 'IGNORE' hook is not supported by "__WARN__", you can
               disable warnings using the empty subroutine:

                   local $SIG{__WARN__} = sub {};

               The routine indicated by $SIG{__DIE__} is called when a fatal
               exception is about to be thrown.  The error message is passed
               as the first argument.  When a "__DIE__" hook routine returns,
               the exception processing continues as it would have in the
               absence of the hook, unless the hook routine itself exits via a
               "goto", a loop exit, or a "die()".  The "__DIE__" handler is
               explicitly disabled during the call, so that you can die from a
               "__DIE__" handler.  Similarly for "__WARN__".

               Due to an implementation glitch, the $SIG{__DIE__} hook is
               called even inside an eval().  Do not use this to rewrite a
               pending exception in $@, or as a bizarre substitute for
               overriding "CORE::GLOBAL::die()".  This strange action at a
               distance may be fixed in a future release so that $SIG{__DIE__}
               is only called if your program is about to exit, as was the
               original intent.  Any other use is deprecated.
                        To see backtrace try starting Perl with -MCarp switch";

               Here the first line will load Carp unless it is the parser who
               called the handler.  The second line will print backtrace and
               die if Carp was available.  The third line will be executed
               only if Carp was not available.

               See "die" in perlfunc, "warn" in perlfunc, "eval" in perlfunc,
               and warnings for additional information.

   Error Indicators
       The variables $@, $!, $^E, and $? contain information about different
       types of error conditions that may appear during execution of a Perl
       program.  The variables are shown ordered by the "distance" between the
       subsystem which reported the error and the Perl process.  They
       correspond to errors detected by the Perl interpreter, C library,
       operating system, or an external program, respectively.

       To illustrate the differences between these variables, consider the
       following Perl expression, which uses a single-quoted string:

           eval q{
               open my $pipe, "/cdrom/install |" or die $!;
               my @res = <$pipe>;
               close $pipe or die "bad pipe: $?, $!";
           };

       After execution of this statement all 4 variables may have been set.

       $@ is set if the string to be "eval"-ed did not compile (this may
       happen if "open" or "close" were imported with bad prototypes), or if
       Perl code executed during evaluation die()d .  In these cases the value
       of $@ is the compile error, or the argument to "die" (which will
       interpolate $! and $?).  (See also Fatal, though.)

       When the eval() expression above is executed, open(), "<PIPE>", and
       "close" are translated to calls in the C run-time library and thence to
       the operating system kernel.  $! is set to the C library's "errno" if
       one of these calls fails.

       Under a few operating systems, $^E may contain a more verbose error
       indicator, such as in this case, "CDROM tray not closed."  Systems that
       do not support extended error messages leave $^E the same as $!.

       Finally, $? may be set to non-0 value if the external program
       /cdrom/install fails.  The upper eight bits reflect specific error
       conditions encountered by the program (the program's exit() value).
       The lower eight bits reflect mode of failure, like signal death and
       core dump information  See wait(2) for details.  In contrast to $! and
       $^E, which are set only if error condition is detected, the variable $?
       is set on each "wait" or pipe "close", overwriting the old value.  This
       is more like $@, which on every eval() is always set on failure and
       cleared on success.

       punctuation or control character.  These names are all reserved for
       special uses by Perl; for example, the all-digits names are used to
       hold data captured by backreferences after a regular expression match.
       Perl has a special syntax for the single-control-character names: It
       understands "^X" (caret "X") to mean the control-"X" character.  For
       example, the notation $^W (dollar-sign caret "W") is the scalar
       variable whose name is the single character control-"W".  This is
       better than typing a literal control-"W" into your program.

       Finally, new in Perl 5.6, Perl variable names may be alphanumeric
       strings that begin with control characters (or better yet, a caret).
       These variables must be written in the form "${^Foo}"; the braces are
       not optional.  "${^Foo}" denotes the scalar variable whose name is a
       control-"F" followed by two "o"'s.  These variables are reserved for
       future special uses by Perl, except for the ones that begin with "^_"
       (control-underscore or caret-underscore).  No control-character name
       that begins with "^_" will acquire a special meaning in any future
       version of Perl; such names may therefore be used safely in programs.
       $^_ itself, however, is reserved.

       Perl identifiers that begin with digits, control characters, or
       punctuation characters are exempt from the effects of the "package"
       declaration and are always forced to be in package "main"; they are
       also exempt from "strict 'vars'" errors.  A few other names are also
       exempt in these ways:

               ENV             STDIN
               INC             STDOUT
               ARGV            STDERR
               ARGVOUT         _
               SIG

       In particular, the new special "${^_XYZ}" variables are always taken to
       be in package "main", regardless of any "package" declarations
       presently in scope.

BUGS
       Due to an unfortunate accident of Perl's implementation, "use English"
       imposes a considerable performance penalty on all regular expression
       matches in a program, regardless of whether they occur in the scope of
       "use English".  For that reason, saying "use English" in libraries is
       strongly discouraged.  See the Devel::SawAmpersand module documentation
       from CPAN ( http://www.cpan.org/modules/by-module/Devel/ ) for more
       information. Writing "use English '-no_match_vars';" avoids the
       performance penalty.

       Having to even think about the $^S variable in your exception handlers
       is simply wrong.  $SIG{__DIE__} as currently implemented invites
       grievous and difficult to track down errors.  Avoid it and use an
       "END{}" or CORE::GLOBAL::die override instead.



perl v5.10.1                      2009-04-18                        PERLVAR(1)
Man Pages Copyright Respective Owners. Site Copyright (C) 1994 - 2014 Hurricane Electric. All Rights Reserved.