Perl runs on numerous operating systems.  While most of them share much
       in common, they also have their own unique features.

       This document is meant to help you to find out what constitutes
       portable Perl code.  That way once you make a decision to write
       portably, you know where the lines are drawn, and you can stay within

       There is a tradeoff between taking full advantage of one particular
       type of computer and taking advantage of a full range of them.
       Naturally, as you broaden your range and become more diverse, the
       common factors drop, and you are left with an increasingly smaller area
       of common ground in which you can operate to accomplish a particular
       task.  Thus, when you begin attacking a problem, it is important to
       consider under which part of the tradeoff curve you want to operate.
       Specifically, you must decide whether it is important that the task
       that you are coding have the full generality of being portable, or
       whether to just get the job done right now.  This is the hardest choice
       to be made.  The rest is easy, because Perl provides many choices,
       whichever way you want to approach your problem.

       Looking at it another way, writing portable code is usually about
       willfully limiting your available choices.  Naturally, it takes
       discipline and sacrifice to do that.  The product of portability and
       convenience may be a constant.  You have been warned.

       Be aware of two important points:

       Not all Perl programs have to be portable
           There is no reason you should not use Perl as a language to glue
           Unix tools together, or to prototype a Macintosh application, or to
           manage the Windows registry.  If it makes no sense to aim for
           portability for one reason or another in a given program, then
           don't bother.

       Nearly all of Perl already is portable
           Don't be fooled into thinking that it is hard to create portable
           Perl code.  It isn't.  Perl tries its level-best to bridge the gaps
           between what's available on different platforms, and all the means
           available to use those features.  Thus almost all Perl code runs on
           any machine without modification.  But there are some significant
           issues in writing portable code, and this document is entirely
           about those issues.

       Here's the general rule: When you approach a task commonly done using a
       whole range of platforms, think about writing portable code.  That way,
       you don't sacrifice much by way of the implementation choices you can
       avail yourself of, and at the same time you can give your users lots of
       platform choices.  On the other hand, when you have to take advantage
       of some unique feature of a particular platform, as is often the case
       with systems programming (whether for Unix, Windows, VMS, etc.),
       consider writing platform-specific code.
       possibly transient information about idiosyncrasies of some of the
       ports, almost all of which are in a state of constant evolution.  Thus,
       this material should be considered a perpetual work in progress ("<IMG
       SRC="yellow_sign.gif" ALT="Under Construction">").

       In most operating systems, lines in files are terminated by newlines.
       Just what is used as a newline may vary from OS to OS.  Unix
       traditionally uses "\012", one type of DOSish I/O uses "\015\012", and
       Mac OS uses "\015".

       Perl uses "\n" to represent the "logical" newline, where what is
       logical may depend on the platform in use.  In MacPerl, "\n" always
       means "\015".  In DOSish perls, "\n" usually means "\012", but when
       accessing a file in "text" mode, perl uses the ":crlf" layer that
       translates it to (or from) "\015\012", depending on whether you're
       reading or writing. Unix does the same thing on ttys in canonical mode.
       "\015\012" is commonly referred to as CRLF.

       To trim trailing newlines from text lines use chomp().  With default
       settings that function looks for a trailing "\n" character and thus
       trims in a portable way.

       When dealing with binary files (or text files in binary mode) be sure
       to explicitly set $/ to the appropriate value for your file format
       before using chomp().

       Because of the "text" mode translation, DOSish perls have limitations
       in using "seek" and "tell" on a file accessed in "text" mode.  Stick to
       "seek"-ing to locations you got from "tell" (and no others), and you
       are usually free to use "seek" and "tell" even in "text" mode.  Using
       "seek" or "tell" or other file operations may be non-portable.  If you
       use "binmode" on a file, however, you can usually "seek" and "tell"
       with arbitrary values in safety.

       A common misconception in socket programming is that "\n" eq "\012"
       everywhere.  When using protocols such as common Internet protocols,
       "\012" and "\015" are called for specifically, and the values of the
       logical "\n" and "\r" (carriage return) are not reliable.

           print SOCKET "Hi there, client!\r\n";      # WRONG
           print SOCKET "Hi there, client!\015\012";  # RIGHT

       However, using "\015\012" (or "\cM\cJ", or "\x0D\x0A") can be tedious
       and unsightly, as well as confusing to those maintaining the code.  As
       such, the Socket module supplies the Right Thing for those who want it.

           use Socket qw(:DEFAULT :crlf);
           print SOCKET "Hi there, client!$CRLF"      # RIGHT

       When reading from a socket, remember that the default input record
       separator $/ is "\n", but robust socket code will recognize as either
       "\012" or "\015\012" as end of line:
               s/$CR?$LF/\n/;   # not sure if socket uses LF or CRLF, OK
           #   s/\015?\012/\n/; # same thing

       This example is preferred over the previous one--even for Unix
       platforms--because now any "\015"'s ("\cM"'s) are stripped out (and
       there was much rejoicing).

       Similarly, functions that return text data--such as a function that
       fetches a web page--should sometimes translate newlines before
       returning the data, if they've not yet been translated to the local
       newline representation.  A single line of code will often suffice:

           $data =~ s/\015?\012/\n/g;
           return $data;

       Some of this may be confusing.  Here's a handy reference to the ASCII
       CR and LF characters.  You can print it out and stick it in your

           LF  eq  \012  eq  \x0A  eq  \cJ  eq  chr(10)  eq  ASCII 10
           CR  eq  \015  eq  \x0D  eq  \cM  eq  chr(13)  eq  ASCII 13

                    | Unix | DOS  | Mac  |
               \n   |  LF  |  LF  |  CR  |
               \r   |  CR  |  CR  |  LF  |
               \n * |  LF  | CRLF |  CR  |
               \r * |  CR  |  CR  |  LF  |
               * text-mode STDIO

       The Unix column assumes that you are not accessing a serial line (like
       a tty) in canonical mode.  If you are, then CR on input becomes "\n",
       and "\n" on output becomes CRLF.

       These are just the most common definitions of "\n" and "\r" in Perl.
       There may well be others.  For example, on an EBCDIC implementation
       such as z/OS (OS/390) or OS/400 (using the ILE, the PASE is ASCII-
       based) the above material is similar to "Unix" but the code numbers

           LF  eq  \025  eq  \x15  eq  \cU  eq  chr(21)  eq  CP-1047 21
           LF  eq  \045  eq  \x25  eq           chr(37)  eq  CP-0037 37
           CR  eq  \015  eq  \x0D  eq  \cM  eq  chr(13)  eq  CP-1047 13
           CR  eq  \015  eq  \x0D  eq  \cM  eq  chr(13)  eq  CP-0037 13

                    | z/OS | OS/400 |
               \n   |  LF  |  LF    |
               \r   |  CR  |  CR    |
               \n * |  LF  |  LF    |
               \r * |  CR  |  CR    |

       decimal), a big-endian host (Motorola, Sparc, PA) reads it as
       0x78563412 (2018915346 in decimal).  Alpha and MIPS can be either:
       Digital/Compaq used/uses them in little-endian mode; SGI/Cray uses them
       in big-endian mode.  To avoid this problem in network (socket)
       connections use the "pack" and "unpack" formats "n" and "N", the
       "network" orders.  These are guaranteed to be portable.

       As of perl 5.10.0, you can also use the ">" and "<" modifiers to force
       big- or little-endian byte-order.  This is useful if you want to store
       signed integers or 64-bit integers, for example.

       You can explore the endianness of your platform by unpacking a data
       structure packed in native format such as:

           print unpack("h*", pack("s2", 1, 2)), "\n";
           # '10002000' on e.g. Intel x86 or Alpha 21064 in little-endian mode
           # '00100020' on e.g. Motorola 68040

       If you need to distinguish between endian architectures you could use
       either of the variables set like so:

           $is_big_endian   = unpack("h*", pack("s", 1)) =~ /01/;
           $is_little_endian = unpack("h*", pack("s", 1)) =~ /^1/;

       Differing widths can cause truncation even between platforms of equal
       endianness.  The platform of shorter width loses the upper parts of the
       number.  There is no good solution for this problem except to avoid
       transferring or storing raw binary numbers.

       One can circumnavigate both these problems in two ways.  Either
       transfer and store numbers always in text format, instead of raw
       binary, or else consider using modules like Data::Dumper and Storable
       (included as of perl 5.8).  Keeping all data as text significantly
       simplifies matters.

       The v-strings are portable only up to v2147483647 (0x7FFFFFFF), that's
       how far EBCDIC, or more precisely UTF-EBCDIC will go.

   Files and Filesystems
       Most platforms these days structure files in a hierarchical fashion.
       So, it is reasonably safe to assume that all platforms support the
       notion of a "path" to uniquely identify a file on the system.  How that
       path is really written, though, differs considerably.

       Although similar, file path specifications differ between Unix,
       Windows, Mac OS, OS/2, VMS, VOS, RISC OS, and probably others.  Unix,
       for example, is one of the few OSes that has the elegant idea of a
       single root directory.

       DOS, OS/2, VMS, VOS, and Windows can work similarly to Unix with "/" as
       path separator, or in their own idiosyncratic ways (such as having
       several root directories and various "unrooted" device files such NIL:
       and LPT:).

       VOS perl can emulate Unix filenames with "/" as path separator.  The
       native pathname characters greater-than, less-than, number-sign, and
       percent-sign are always accepted.

       RISC OS perl can emulate Unix filenames with "/" as path separator, or
       go native and use "." for path separator and ":" to signal filesystems
       and disk names.

       Don't assume Unix filesystem access semantics: that read, write, and
       execute are all the permissions there are, and even if they exist, that
       their semantics (for example what do r, w, and x mean on a directory)
       are the Unix ones.  The various Unix/POSIX compatibility layers usually
       try to make interfaces like chmod() work, but sometimes there simply is
       no good mapping.

       If all this is intimidating, have no (well, maybe only a little) fear.
       There are modules that can help.  The File::Spec modules provide
       methods to do the Right Thing on whatever platform happens to be
       running the program.

           use File::Spec::Functions;
           chdir(updir());        # go up one directory
           my $file = catfile(curdir(), 'temp', 'file.txt');
           # on Unix and Win32, './temp/file.txt'
           # on Mac OS Classic, ':temp:file.txt'
           # on VMS, '[.temp]file.txt'

       File::Spec is available in the standard distribution as of version
       5.004_05.  File::Spec::Functions is only in File::Spec 0.7 and later,
       and some versions of perl come with version 0.6.  If File::Spec is not
       updated to 0.7 or later, you must use the object-oriented interface
       from File::Spec (or upgrade File::Spec).

       In general, production code should not have file paths hardcoded.
       Making them user-supplied or read from a configuration file is better,
       keeping in mind that file path syntax varies on different machines.

       This is especially noticeable in scripts like Makefiles and test
       suites, which often assume "/" as a path separator for subdirectories.

       Also of use is File::Basename from the standard distribution, which
       splits a pathname into pieces (base filename, full path to directory,
       and file suffix).

       Even when on a single platform (if you can call Unix a single
       platform), remember not to count on the existence or the contents of
       particular system-specific files or directories, like /etc/passwd,
       /etc/sendmail.conf, /etc/resolv.conf, or even /tmp/.  For example,
       /etc/passwd may exist but not contain the encrypted passwords, because
       the system is using some form of enhanced security.  Or it may not
       contain all the accounts, because the system is using NIS.  If code
       does need to rely on such a file, include a description of the file and
       its format in the code's documentation, then make it easy for the user
       Likewise, when using the AutoSplit module, try to keep your functions
       to 8.3 naming and case-insensitive conventions; or, at the least, make
       it so the resulting files have a unique (case-insensitively) first 8

       Whitespace in filenames is tolerated on most systems, but not all, and
       even on systems where it might be tolerated, some utilities might
       become confused by such whitespace.

       Many systems (DOS, VMS ODS-2) cannot have more than one "." in their

       Don't assume ">" won't be the first character of a filename.  Always
       use "<" explicitly to open a file for reading, or even better, use the
       three-arg version of open, unless you want the user to be able to
       specify a pipe open.

           open my $fh, '<', $existing_file) or die $!;

       If filenames might use strange characters, it is safest to open it with
       "sysopen" instead of "open".  "open" is magic and can translate
       characters like ">", "<", and "|", which may be the wrong thing to do.
       (Sometimes, though, it's the right thing.)  Three-arg open can also
       help protect against this translation in cases where it is undesirable.

       Don't use ":" as a part of a filename since many systems use that for
       their own semantics (Mac OS Classic for separating pathname components,
       many networking schemes and utilities for separating the nodename and
       the pathname, and so on).  For the same reasons, avoid "@", ";" and

       Don't assume that in pathnames you can collapse two leading slashes
       "//" into one: some networking and clustering filesystems have special
       semantics for that.  Let the operating system to sort it out.

       The portable filename characters as defined by ANSI C are

        a b c d e f g h i j k l m n o p q r t u v w x y z
        A B C D E F G H I J K L M N O P Q R T U V W X Y Z
        0 1 2 3 4 5 6 7 8 9
        . _ -

       and the "-" shouldn't be the first character.  If you want to be
       hypercorrect, stay case-insensitive and within the 8.3 naming
       convention (all the files and directories have to be unique within one
       directory if their names are lowercased and truncated to eight
       characters before the ".", if any, and to three characters after the
       ".", if any).  (And do not use "."s in directory names.)

   System Interaction
       Not all platforms provide a command line.  These are usually platforms
       that rely primarily on a Graphical User Interface (GUI) for user
       interaction.  A program requiring a command line interface might not
       work everywhere.  This is probably for the user of the program to deal
       Don't assume that write/modify permission on a directory gives the
       right to add or delete files/directories in that directory.  That is
       filesystem specific: in some filesystems you need write/modify
       permission also (or even just) in the file/directory itself.  In some
       filesystems (AFS, DFS) the permission to add/delete directory entries
       is a completely separate permission.

       Don't assume that a single "unlink" completely gets rid of the file:
       some filesystems (most notably the ones in VMS) have versioned
       filesystems, and unlink() removes only the most recent one (it doesn't
       remove all the versions because by default the native tools on those
       platforms remove just the most recent version, too).  The portable
       idiom to remove all the versions of a file is

           1 while unlink "file";

       This will terminate if the file is undeleteable for some reason
       (protected, not there, and so on).

       Don't count on a specific environment variable existing in %ENV.  Don't
       count on %ENV entries being case-sensitive, or even case-preserving.
       Don't try to clear %ENV by saying "%ENV = ();", or, if you really have
       to, make it conditional on "$^O ne 'VMS'" since in VMS the %ENV table
       is much more than a per-process key-value string table.

       On VMS, some entries in the %ENV hash are dynamically created when
       their key is used on a read if they did not previously exist.  The
       values for $ENV{HOME}, $ENV{TERM}, $ENV{HOME}, and $ENV{USER}, are
       known to be dynamically generated.  The specific names that are
       dynamically generated may vary with the version of the C library on
       VMS, and more may exist than is documented.

       On VMS by default, changes to the %ENV hash are persistent after the
       process exits.  This can cause unintended issues.

       Don't count on signals or %SIG for anything.

       Don't count on filename globbing.  Use "opendir", "readdir", and
       "closedir" instead.

       Don't count on per-program environment variables, or per-program
       current directories.

       Don't count on specific values of $!, neither numeric nor especially
       the strings values. Users may switch their locales causing error
       messages to be translated into their languages.  If you can trust a
       POSIXish environment, you can portably use the symbols defined by the
       Errno module, like ENOENT.  And don't trust on the values of $!  at all
       except immediately after a failed system call.

   Command names versus file pathnames
       Don't assume that the name used to invoke a command or program with
       "system" or "exec" can also be used to test for the existence of the
       file that holds the executable code for that command or program.
       file name.

       To convert $^X to a file pathname, taking account of the requirements
       of the various operating system possibilities, say:

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

       To convert $Config{perlpath} to a file pathname, say:

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

       Don't assume that you can reach the public Internet.

       Don't assume that there is only one way to get through firewalls to the
       public Internet.

       Don't assume that you can reach outside world through any other port
       than 80, or some web proxy.  ftp is blocked by many firewalls.

       Don't assume that you can send email by connecting to the local SMTP

       Don't assume that you can reach yourself or any node by the name
       'localhost'.  The same goes for ''.  You will have to try

       Don't assume that the host has only one network card, or that it can't
       bind to many virtual IP addresses.

       Don't assume a particular network device name.

       Don't assume a particular set of ioctl()s will work.

       Don't assume that you can ping hosts and get replies.

       Don't assume that any particular port (service) will respond.

       Don't assume that Sys::Hostname (or any other API or command) returns
       either a fully qualified hostname or a non-qualified hostname: it all
       depends on how the system had been configured.  Also remember that for
       things such as DHCP and NAT, the hostname you get back might not be
       very useful.

       All the above "don't":s may look daunting, and they are, but the key is
       to degrade gracefully if one cannot reach the particular network
       service one wants.  Croaking or hanging do not look very professional.

       platform-dependent way.  Thus, you should seldom depend on them to
       produce consistent results. (Then again, if you're calling netstat -a,
       you probably don't expect it to run on both Unix and CP/M.)

       One especially common bit of Perl code is opening a pipe to sendmail:

           open(MAIL, '|/usr/lib/sendmail -t')
               or die "cannot fork sendmail: $!";

       This is fine for systems programming when sendmail is known to be
       available.  But it is not fine for many non-Unix systems, and even some
       Unix systems that may not have sendmail installed.  If a portable
       solution is needed, see the various distributions on CPAN that deal
       with it.  Mail::Mailer and Mail::Send in the MailTools distribution are
       commonly used, and provide several mailing methods, including mail,
       sendmail, and direct SMTP (via Net::SMTP) if a mail transfer agent is
       not available.  Mail::Sendmail is a standalone module that provides
       simple, platform-independent mailing.

       The Unix System V IPC ("msg*(), sem*(), shm*()") is not available even
       on all Unix platforms.

       Do not use either the bare result of "pack("N", 10, 20, 30, 40)" or
       bare v-strings (such as "v10.20.30.40") to represent IPv4 addresses:
       both forms just pack the four bytes into network order.  That this
       would be equal to the C language "in_addr" struct (which is what the
       socket code internally uses) is not guaranteed.  To be portable use the
       routines of the Socket extension, such as "inet_aton()", "inet_ntoa()",
       and "sockaddr_in()".

       The rule of thumb for portable code is: Do it all in portable Perl, or
       use a module (that may internally implement it with platform-specific
       code, but expose a common interface).

   External Subroutines (XS)
       XS code can usually be made to work with any platform, but dependent
       libraries, header files, etc., might not be readily available or
       portable, or the XS code itself might be platform-specific, just as
       Perl code might be.  If the libraries and headers are portable, then it
       is normally reasonable to make sure the XS code is portable, too.

       A different type of portability issue arises when writing XS code:
       availability of a C compiler on the end-user's system.  C brings with
       it its own portability issues, and writing XS code will expose you to
       some of those.  Writing purely in Perl is an easier way to achieve

   Standard Modules
       In general, the standard modules work across platforms.  Notable
       exceptions are the CPAN module (which currently makes connections to
       external programs that may not be available), platform-specific modules
       (like ExtUtils::MM_VMS), and DBM modules.

       There is no one DBM module available on all platforms.  SDBM_File and
       $ENV{TZ}, and even if it is, don't assume that you can control the
       timezone through that variable.  Don't assume anything about the three-
       letter timezone abbreviations (for example that MST would be the
       Mountain Standard Time, it's been known to stand for Moscow Standard
       Time).  If you need to use timezones, express them in some unambiguous
       format like the exact number of minutes offset from UTC, or the POSIX
       timezone format.

       Don't assume that the epoch starts at 00:00:00, January 1, 1970,
       because that is OS- and implementation-specific.  It is better to store
       a date in an unambiguous representation.  The ISO 8601 standard defines
       YYYY-MM-DD as the date format, or YYYY-MM-DDTHH:MM:SS (that's a literal
       "T" separating the date from the time).  Please do use the ISO 8601
       instead of making us guess what date 02/03/04 might be.  ISO 8601 even
       sorts nicely as-is.  A text representation (like "1987-12-18") can be
       easily converted into an OS-specific value using a module like
       Date::Parse.  An array of values, such as those returned by
       "localtime", can be converted to an OS-specific representation using

       When calculating specific times, such as for tests in time or date
       modules, it may be appropriate to calculate an offset for the epoch.

           require Time::Local;
           my $offset = Time::Local::timegm(0, 0, 0, 1, 0, 70);

       The value for $offset in Unix will be 0, but in Mac OS Classic will be
       some large number.  $offset can then be added to a Unix time value to
       get what should be the proper value on any system.

   Character sets and character encoding
       Assume very little about character sets.

       Assume nothing about numerical values ("ord", "chr") of characters.  Do
       not use explicit code point ranges (like \xHH-\xHH); use for example
       symbolic character classes like "[:print:]".

       Do not assume that the alphabetic characters are encoded contiguously
       (in the numeric sense).  There may be gaps.

       Do not assume anything about the ordering of the characters.  The
       lowercase letters may come before or after the uppercase letters; the
       lowercase and uppercase may be interlaced so that both "a" and "A" come
       before "b"; the accented and other international characters may be
       interlaced so that ae comes before "b".

       If you may assume POSIX (a rather large assumption), you may read more
       about the POSIX locale system from perllocale.  The locale system at
       least attempts to make things a little bit more portable, or at least
       more convenient and native-friendly for non-English users.  The system
       affects character sets and encoding, and date and time
       formatting--amongst other things.

       embedding the bytes as-is.  If you want to write your code in UTF-8,
       you can use the "utf8".

   System Resources
       If your code is destined for systems with severely constrained (or
       missing!) virtual memory systems then you want to be especially mindful
       of avoiding wasteful constructs such as:

           my @lines = <$very_large_file>;            # bad

           while (<$fh>) {$file .= $_}                # sometimes bad
           my $file = join('', <$fh>);                # better

       The last two constructs may appear unintuitive to most people.  The
       first repeatedly grows a string, whereas the second allocates a large
       chunk of memory in one go.  On some systems, the second is more
       efficient that the first.

       Most multi-user platforms provide basic levels of security, usually
       implemented at the filesystem level.  Some, however, unfortunately do
       not.  Thus the notion of user id, or "home" directory, or even the
       state of being logged-in, may be unrecognizable on many platforms.  If
       you write programs that are security-conscious, it is usually best to
       know what type of system you will be running under so that you can
       write code explicitly for that platform (or class of platforms).

       Don't assume the Unix filesystem access semantics: the operating system
       or the filesystem may be using some ACL systems, which are richer
       languages than the usual rwx.  Even if the rwx exist, their semantics
       might be different.

       (From security viewpoint testing for permissions before attempting to
       do something is silly anyway: if one tries this, there is potential for
       race conditions. Someone or something might change the permissions
       between the permissions check and the actual operation.  Just try the

       Don't assume the Unix user and group semantics: especially, don't
       expect the $< and $> (or the $( and $)) to work for switching
       identities (or memberships).

       Don't assume set-uid and set-gid semantics. (And even if you do, think
       twice: set-uid and set-gid are a known can of security worms.)

       For those times when it is necessary to have platform-specific code,
       consider keeping the platform-specific code in one place, making
       porting to other platforms easier.  Use the Config module and the
       special variable $^O to differentiate platforms, as described in

       Be careful in the tests you supply with your module or programs.
       Module code may be fully portable, but its tests might not be.  This
       Modules uploaded to CPAN are tested by a variety of volunteers on
       different platforms.  These CPAN testers are notified by mail of each
       new upload, and reply to the list with PASS, FAIL, NA (not applicable
       to this platform), or UNKNOWN (unknown), along with any relevant

       The purpose of the testing is twofold: one, to help developers fix any
       problems in their code that crop up because of lack of testing on other
       platforms; two, to provide users with information about whether a given
       module works on a given platform.

       Also see:

       o   Mailing list:

       o   Testing results: <>

       Perl is built with a $^O variable that indicates the operating system
       it was built on.  This was implemented to help speed up code that would
       otherwise have to "use Config" and use the value of $Config{osname}.
       Of course, to get more detailed information about the system, looking
       into %Config is certainly recommended.

       %Config cannot always be trusted, however, because it was built at
       compile time.  If perl was built in one place, then transferred
       elsewhere, some values may be wrong.  The values may even have been
       edited after the fact.

       Perl works on a bewildering variety of Unix and Unix-like platforms
       (see e.g. most of the files in the hints/ directory in the source code
       kit).  On most of these systems, the value of $^O (hence
       $Config{'osname'}, too) is determined either by lowercasing and
       stripping punctuation from the first field of the string returned by
       typing "uname -a" (or a similar command) at the shell prompt or by
       testing the file system for the presence of uniquely named files such
       as a kernel or header file.  Here, for example, are a few of the more
       popular Unix flavors:

           uname         $^O        $Config{'archname'}
           AIX           aix        aix
           BSD/OS        bsdos      i386-bsdos
           Darwin        darwin     darwin
           dgux          dgux       AViiON-dgux
           DYNIX/ptx     dynixptx   i386-dynixptx
           FreeBSD       freebsd    freebsd-i386
           Haiku         haiku      BePC-haiku
           Linux         linux      arm-linux
           Linux         linux      i386-linux
           Linux         linux      i586-linux
           Linux         linux      ppc-linux
           HP-UX         hpux       PA-RISC1.1
           SunOS         solaris    sun4-solaris
           SunOS         solaris    i86pc-solaris
           SunOS4        sunos      sun4-sunos

       Because the value of $Config{archname} may depend on the hardware
       architecture, it can vary more than the value of $^O.

   DOS and Derivatives
       Perl has long been ported to Intel-style microcomputers running under
       systems like PC-DOS, MS-DOS, OS/2, and most Windows platforms you can
       bring yourself to mention (except for Windows CE, if you count that).
       Users familiar with COMMAND.COM or CMD.EXE style shells should be aware
       that each of these file specifications may have subtle differences:

           my $filespec0 = "c:/foo/bar/file.txt";
           my $filespec1 = "c:\\foo\\bar\\file.txt";
           my $filespec2 = 'c:\foo\bar\file.txt';
           my $filespec3 = 'c:\\foo\\bar\\file.txt';

       System calls accept either "/" or "\" as the path separator.  However,
       many command-line utilities of DOS vintage treat "/" as the option
       prefix, so may get confused by filenames containing "/".  Aside from
       calling any external programs, "/" will work just fine, and probably
       better, as it is more consistent with popular usage, and avoids the
       problem of remembering what to backwhack and what not to.

       The DOS FAT filesystem can accommodate only "8.3" style filenames.
       Under the "case-insensitive, but case-preserving" HPFS (OS/2) and NTFS
       (NT) filesystems you may have to be careful about case returned with
       functions like "readdir" or used with functions like "open" or

       DOS also treats several filenames as special, such as AUX, PRN, NUL,
       CON, COM1, LPT1, LPT2, etc.  Unfortunately, sometimes these filenames
       won't even work if you include an explicit directory prefix.  It is
       best to avoid such filenames, if you want your code to be portable to
       DOS and its derivatives.  It's hard to know what these all are,

       Users of these operating systems may also wish to make use of scripts
       such as pl2bat.bat or pl2cmd to put wrappers around your scripts.

       Newline ("\n") is translated as "\015\012" by STDIO when reading from
       and writing to files (see "Newlines").  "binmode(FILEHANDLE)" will keep
       "\n" translated as "\012" for that filehandle.  Since it is a no-op on
       other systems, "binmode" should be used for cross-platform code that
       deals with binary data.  That's assuming you realize in advance that
       your data is in binary.  General-purpose programs should often assume
       nothing about their data.

       The $^O variable and the $Config{archname} values for various DOSish
       perls are as follows:

            OS            $^O      $Config{archname}   ID    Version
            Windows XP    MSWin32    MSWin32-x86       2      5 01
            Windows 2003  MSWin32    MSWin32-x86       2      5 02
            Windows Vista MSWin32    MSWin32-x86       2      6 00
            Windows 7     MSWin32    MSWin32-x86       2      6 01
            Windows 7     MSWin32    MSWin32-x64       2      6 01
            Windows 2008  MSWin32    MSWin32-x86       2      6 01
            Windows 2008  MSWin32    MSWin32-x64       2      6 01
            Windows CE    MSWin32    ?                 3
            Cygwin        cygwin     cygwin

       The various MSWin32 Perl's can distinguish the OS they are running on
       via the value of the fifth element of the list returned from
       Win32::GetOSVersion().  For example:

           if ($^O eq 'MSWin32') {
               my @os_version_info = Win32::GetOSVersion();
               print +('3.1','95','NT')[$os_version_info[4]],"\n";

       There are also Win32::IsWinNT() and Win32::IsWin95(), try "perldoc
       Win32", and as of libwin32 0.19 (not part of the core Perl
       distribution) Win32::GetOSName().  The very portable POSIX::uname()
       will work too:

           c:\> perl -MPOSIX -we "print join '|', uname"
           Windows NT|moonru|5.0|Build 2195 (Service Pack 2)|x86

       Also see:

       o   The djgpp environment for DOS, <> and

       o   The EMX environment for DOS, OS/2, etc.,
           <>  Also perlos2.

       o   Build instructions for Win32 in perlwin32, or under the Cygnus
           environment in perlcygwin.

       o   The "Win32::*" modules in Win32.

       o   The ActiveState Pages, <>

       o   The Cygwin environment for Win32; README.cygwin (installed as
           perlcygwin), <>

       o   The U/WIN environment for Win32,

       o   Build instructions for OS/2, perlos2

       Perl on VMS is discussed in perlvms in the perl distribution.

       The official name of VMS as of this writing is OpenVMS.
       Interacting with Perl from the Digital Command Language (DCL) shell
       often requires a different set of quotation marks than Unix shells do.
       For example:

           $ perl -e "print ""Hello, world.\n"""
           Hello, world.

       There are several ways to wrap your perl scripts in DCL .COM files, if
       you are so inclined.  For example:

           $ write sys$output "Hello from DCL!"
           $ if p1 .eqs. ""
           $ then perl -x 'f$environment("PROCEDURE")
           $ else perl -x - 'p1 'p2 'p3 'p4 'p5 'p6 'p7 'p8
           $ deck/dollars="__END__"

           print "Hello from Perl!\n";

           $ endif

       Do take care with "$ ASSIGN/nolog/user SYS$COMMAND: SYS$INPUT" if your
       perl-in-DCL script expects to do things like "$read = <STDIN>;".

       The VMS operating system has two filesystems, known as ODS-2 and ODS-5.

       For ODS-2, filenames are in the format "name.extension;version".  The
       maximum length for filenames is 39 characters, and the maximum length
       for extensions is also 39 characters.  Version is a number from 1 to
       32767.  Valid characters are "/[A-Z0-9$_-]/".

       The ODS-2 filesystem is case-insensitive and does not preserve case.
       Perl simulates this by converting all filenames to lowercase

       For ODS-5, filenames may have almost any character in them and can
       include Unicode characters.  Characters that could be misinterpreted by
       the DCL shell or file parsing utilities need to be prefixed with the
       "^" character, or replaced with hexadecimal characters prefixed with
       the "^" character.  Such prefixing is only needed with the pathnames
       are in VMS format in applications.  Programs that can accept the Unix
       format of pathnames do not need the escape characters.  The maximum
       length for filenames is 255 characters.  The ODS-5 file system can
       handle both a case preserved and a case sensitive mode.

       ODS-5 is only available on the OpenVMS for 64 bit platforms.

       Support for the extended file specifications is being done as optional
       settings to preserve backward compatibility with Perl scripts that
       assume the previous VMS limitations.

       In general routines on VMS that get a Unix format file specification
       should return it in a Unix format, and when they get a VMS format
       treating VMS and Unix filenames interchangeably.  Without the extended
       character set enabled, this behavior will mostly be maintained for
       backwards compatibility.

       When extended characters are enabled with ODS-5, the handling of Unix
       formatted file specifications is to that of a Unix system.

       VMS file specifications without extensions have a trailing dot.  An
       equivalent Unix file specification should not show the trailing dot.

       The result of all of this, is that for VMS, for portable scripts, you
       can not depend on Perl to present the filenames in lowercase, to be
       case sensitive, and that the filenames could be returned in either Unix
       or VMS format.

       And if a routine returns a file specification, unless it is intended to
       convert it, it should return it in the same format as it found it.

       "readdir" by default has traditionally returned lowercased filenames.
       When the ODS-5 support is enabled, it will return the exact case of the
       filename on the disk.

       Files without extensions have a trailing period on them, so doing a
       "readdir" in the default mode with a file named A.;5 will return a.
       when VMS is (though that file could be opened with "open(FH, 'A')").

       With support for extended file specifications and if "opendir" was
       given a Unix format directory, a file named A.;5 will return a and
       optionally in the exact case on the disk.  When "opendir" is given a
       VMS format directory, then "readdir" should return a., and again with
       the optionally the exact case.

       RMS had an eight level limit on directory depths from any rooted
       logical (allowing 16 levels overall) prior to VMS 7.2, and even with
       versions of VMS on VAX up through 7.3.  Hence
       "PERL_ROOT:[LIB.]" is a valid directory specification but
       "PERL_ROOT:[LIB.]" is not.  Makefile.PL authors might
       have to take this into account, but at least they can refer to the
       former as "/PERL_ROOT/lib/2/3/4/5/6/7/8/".

       Pumpkings and module integrators can easily see whether files with too
       many directory levels have snuck into the core by running the following
       in the top-level source directory:

        $ perl -ne "$_=~s/\s+.*//; print if scalar(split /\//) > 8;" < MANIFEST

       The VMS::Filespec module, which gets installed as part of the build
       process on VMS, is a pure Perl module that can easily be installed on
       non-VMS platforms and can be helpful for conversions to and from RMS
       native formats.  It is also now the only way that you should check to
       see if VMS is in a case sensitive mode.

       What "\n" represents depends on the type of file opened.  It usually
       represents "\012" but it could also be "\015", "\012", "\015\012",
       that you are running on without resorting to loading all of %Config you
       can examine the content of the @INC array like so:

           if (grep(/VMS_AXP/, @INC)) {
               print "I'm on Alpha!\n";

           } elsif (grep(/VMS_VAX/, @INC)) {
               print "I'm on VAX!\n";

           } elsif (grep(/VMS_IA64/, @INC)) {
               print "I'm on IA64!\n";

           } else {
               print "I'm not so sure about where $^O is...\n";

       In general, the significant differences should only be if Perl is
       running on VMS_VAX or one of the 64 bit OpenVMS platforms.

       On VMS, perl determines the UTC offset from the
       "SYS$TIMEZONE_DIFFERENTIAL" logical name.  Although the VMS epoch began
       at 17-NOV-1858 00:00:00.00, calls to "localtime" are adjusted to count
       offsets from 01-JAN-1970 00:00:00.00, just like Unix.

       Also see:

       o   README.vms (installed as README_vms), perlvms

       o   vmsperl list,

       o   vmsperl on the web, <>

       Perl on VOS (also known as OpenVOS) is discussed in README.vos in the
       perl distribution (installed as perlvos).  Perl on VOS can accept
       either VOS- or Unix-style file specifications as in either of the

           $ perl -ne "print if /perl_setup/i" >system>notices
           $ perl -ne "print if /perl_setup/i" /system/notices

       or even a mixture of both as in:

           $ perl -ne "print if /perl_setup/i" >system/notices

       Even though VOS allows the slash character to appear in object names,
       because the VOS port of Perl interprets it as a pathname delimiting
       character, VOS files, directories, or links whose names contain a slash
       character cannot be processed.  Such files must be renamed before they
       can be processed by Perl.

       Older releases of VOS (prior to OpenVOS Release 17.0) limit file names
       to 32 or fewer characters, prohibit file names from starting with a "-"
       character, and prohibit file names from containing any character
       apostrophe-period, leading or trailing space, and leading or trailing
       apostrophe.  Although an extended file name is limited to 255
       characters, a path name is still limited to 256 characters.

       The value of $^O on VOS is "vos".  To determine the architecture that
       you are running on without resorting to loading all of %Config you can
       examine the content of the @INC array like so:

           if ($^O =~ /vos/) {
               print "I'm on a Stratus box!\n";
           } else {
               print "I'm not on a Stratus box!\n";

       Also see:

       o   README.vos (installed as perlvos)

       o   The VOS mailing list.

           There is no specific mailing list for Perl on VOS.  You can contact
           the Stratus Technologies Customer Assistance Center (CAC) for your
           region, or you can use the contact information located in the
           distribution files on the Stratus Anonymous FTP site.

       o   Stratus Technologies on the web at <>

       o   VOS Open-Source Software on the web at

   EBCDIC Platforms
       Recent versions of Perl have been ported to platforms such as OS/400 on
       AS/400 minicomputers as well as OS/390, VM/ESA, and BS2000 for S/390
       Mainframes.  Such computers use EBCDIC character sets internally
       (usually Character Code Set ID 0037 for OS/400 and either 1047 or
       POSIX-BC for S/390 systems).  On the mainframe perl currently works
       under the "Unix system services for OS/390" (formerly known as
       OpenEdition), VM/ESA OpenEdition, or the BS200 POSIX-BC system (BS2000
       is supported in perl 5.6 and greater).  See perlos390 for details.
       Note that for OS/400 there is also a port of Perl 5.8.1/5.10.0 or later
       to the PASE which is ASCII-based (as opposed to ILE which is EBCDIC-
       based), see perlos400.

       As of R2.5 of USS for OS/390 and Version 2.3 of VM/ESA these Unix sub-
       systems do not support the "#!" shebang trick for script invocation.
       Hence, on OS/390 and VM/ESA perl scripts can be executed with a header
       similar to the following simple script:

           : # use perl
               eval 'exec /usr/local/bin/perl -S $0 ${1+"$@"}'
                   if 0;
           #!/usr/local/bin/perl     # just a comment really

       This will invoke the perl script in the root of the QOpenSys
       file system.  On the AS/400 calls to "system" or backticks must use CL

       On these platforms, bear in mind that the EBCDIC character set may have
       an effect on what happens with some perl functions (such as "chr",
       "pack", "print", "printf", "ord", "sort", "sprintf", "unpack"), as well
       as bit-fiddling with ASCII constants using operators like "^", "&" and
       "|", not to mention dealing with socket interfaces to ASCII computers
       (see "Newlines").

       Fortunately, most web servers for the mainframe will correctly
       translate the "\n" in the following statement to its ASCII equivalent
       ("\r" is the same under both Unix and OS/390):

           print "Content-type: text/html\r\n\r\n";

       The values of $^O on some of these platforms includes:

           uname         $^O        $Config{'archname'}
           OS/390        os390      os390
           OS400         os400      os400
           POSIX-BC      posix-bc   BS2000-posix-bc

       Some simple tricks for determining if you are running on an EBCDIC
       platform could include any of the following (perhaps all):

           if ("\t" eq "\005")   { print "EBCDIC may be spoken here!\n"; }

           if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; }

           if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; }

       One thing you may not want to rely on is the EBCDIC encoding of
       punctuation characters since these may differ from code page to code
       page (and once your module or script is rumoured to work with EBCDIC,
       folks will want it to work with all EBCDIC character sets).

       Also see:

       o   perlos390, README.os390, perlbs2000, perlebcdic.

       o   The list is for discussion of porting issues as
           well as general usage issues for all EBCDIC Perls.  Send a message
           body of "subscribe perl-mvs" to

       o   AS/400 Perl information at <> as
           well as on CPAN in the ports/ directory.

   Acorn RISC OS
       Because Acorns use ASCII with newlines ("\n") in text files as "\012"
       like Unix, and because Unix filename emulation is turned on by default,


           Special_Field is not usually present, but may contain . and $ .
           Filesystem =~ m|[A-Za-z0-9_]|
           DsicName   =~ m|[A-Za-z0-9_/]|
           $ represents the root directory
           . is the path separator
           @ is the current directory (per filesystem but machine global)
           ^ is the parent directory
           Directory and File =~ m|[^\0- "\.\$\%\&:\@\\^\|\177]+|

       The default filename translation is roughly "tr|/.|./|;"

       Note that ""ADFS::HardDisk.$.File" ne 'ADFS::HardDisk.$.File'" and that
       the second stage of "$" interpolation in regular expressions will fall
       foul of the $. if scripts are not careful.

       Logical paths specified by system variables containing comma-separated
       search lists are also allowed; hence "System:Modules" is a valid
       filename, and the filesystem will prefix "Modules" with each section of
       "System$Path" until a name is made that points to an object on disk.
       Writing to a new file "System:Modules" would be allowed only if
       "System$Path" contains a single item list.  The filesystem will also
       expand system variables in filenames if enclosed in angle brackets, so
       "<System$Dir>.Modules" would look for the file
       "$ENV{'System$Dir'} . 'Modules'".  The obvious implication of this is
       that fully qualified filenames can start with "<>" and should be
       protected when "open" is used for input.

       Because "." was in use as a directory separator and filenames could not
       be assumed to be unique after 10 characters, Acorn implemented the C
       compiler to strip the trailing ".c" ".h" ".s" and ".o" suffix from
       filenames specified in source code and store the respective files in
       subdirectories named after the suffix.  Hence files are translated:

           C:foo.h        (logical path variable)
           sys/os.h        sys.h.os       (C compiler groks Unix-speak)
           10charname.c    c.10charname
           10charname.o    o.10charname
           11charname_.c   c.11charname   (assuming filesystem truncates at 10)

       The Unix emulation library's translation of filenames to native assumes
       that this sort of translation is required, and it allows a user-defined
       list of known suffixes that it will transpose in this fashion.  This
       may seem transparent, but consider that with these rules foo/bar/baz.h
       and foo/bar/h/baz both map to, and that "readdir" and
       "glob" cannot and do not attempt to emulate the reverse mapping.  Other
       "."'s in filenames are translated to "/".

       As implied above, the environment accessed through %ENV is global, and
       the convention is that program specific environment variables are of
       the form "Program$Name".  Each filesystem maintains a current
       The desire of users to express filenames of the form "<Foo$Dir>.Bar" on
       the command line unquoted causes problems, too: "``" command output
       capture has to perform a guessing game.  It assumes that a string
       "<[^<>]+\$[^<>]>" is a reference to an environment variable, whereas
       anything else involving "<" or ">" is redirection, and generally
       manages to be 99% right.  Of course, the problem remains that scripts
       cannot rely on any Unix tools being available, or that any tools found
       have Unix-like command line arguments.

       Extensions and XS are, in theory, buildable by anyone using free tools.
       In practice, many don't, as users of the Acorn platform are used to
       binary distributions.  MakeMaker does run, but no available make
       currently copes with MakeMaker's makefiles; even if and when this
       should be fixed, the lack of a Unix-like shell will cause problems with
       makefile rules, especially lines of the form "cd sdbm && make all", and
       anything using quoting.

       "RISC OS" is the proper name for the operating system, but the value in
       $^O is "riscos" (because we don't like shouting).

   Other perls
       Perl has been ported to many platforms that do not fit into any of the
       categories listed above.  Some, such as AmigaOS, QNX, Plan 9, and VOS,
       have been well-integrated into the standard Perl source code kit.  You
       may need to see the ports/ directory on CPAN for information, and
       possibly binaries, for the likes of: aos, Atari ST, lynxos, riscos,
       Novell Netware, Tandem Guardian, etc.  (Yes, we know that some of these
       OSes may fall under the Unix category, but we are not a standards

       Some approximate operating system names and their $^O values in the
       "OTHER" category include:

           OS            $^O        $Config{'archname'}
           Amiga DOS     amigaos    m68k-amigos

       See also:

       o   Amiga, README.amiga (installed as perlamiga).

       o   A free perl5-based PERL.NLM for Novell Netware is available in
           precompiled binary and source code form from
           <> as well as from CPAN.

       o   Plan 9, README.plan9

       Listed below are functions that are either completely unimplemented or
       else have been implemented differently on various platforms.  Following
       each description will be, in parentheses, a list of platforms that the
       description applies to.

       The list may well be incomplete, or even wrong in some places.  When in

   Alphabetical Listing of Perl Functions
       -X      "-w" only inspects the read-only file attribute
               (FILE_ATTRIBUTE_READONLY), which determines whether the
               directory can be deleted, not whether it can be written to.
               Directories always have read and write access unless denied by
               discretionary access control lists (DACLs).  (Win32)

               "-r", "-w", "-x", and "-o" tell whether the file is accessible,
               which may not reflect UIC-based file protections.  (VMS)

               "-s" by name on an open file will return the space reserved on
               disk, rather than the current extent.  "-s" on an open
               filehandle returns the current size.  (RISC OS)

               "-R", "-W", "-X", "-O" are indistinguishable from "-r", "-w",
               "-x", "-o". (Win32, VMS, RISC OS)

               "-g", "-k", "-l", "-u", "-A" are not particularly meaningful.
               (Win32, VMS, RISC OS)

               "-p" is not particularly meaningful. (VMS, RISC OS)

               "-d" is true if passed a device spec without an explicit
               directory.  (VMS)

               "-x" (or "-X") determine if a file ends in one of the
               executable suffixes.  "-S" is meaningless.  (Win32)

               "-x" (or "-X") determine if a file has an executable file type.
               (RISC OS)

       alarm   Emulated using timers that must be explicitly polled whenever
               Perl wants to dispatch "safe signals" and therefore cannot
               interrupt blocking system calls.  (Win32)

       atan2   Due to issues with various CPUs, math libraries, compilers, and
               standards, results for "atan2()" may vary depending on any
               combination of the above.  Perl attempts to conform to the Open
               Group/IEEE standards for the results returned from "atan2()",
               but cannot force the issue if the system Perl is run on does
               not allow it.  (Tru64, HP-UX 10.20)

               The current version of the standards for "atan2()" is available

       binmode Meaningless.  (RISC OS)

               Reopens file and restores pointer; if function fails,
               underlying filehandle may be closed, or pointer may be in a
               different position.  (VMS)

               The value returned by "tell" may be affected after the call,
               and the filehandle may be flushed. (Win32)

       chown   Not implemented. (Win32, Plan 9, RISC OS)

               Does nothing, but won't fail. (Win32)

               A little funky, because VOS's notion of ownership is a little
               funky (VOS).

       chroot  Not implemented. (Win32, VMS, Plan 9, RISC OS, VOS)

       crypt   May not be available if library or source was not provided when
               building perl. (Win32)

               Not implemented. (VMS, Plan 9, VOS)

       dbmopen Not implemented. (VMS, Plan 9, VOS)

       dump    Not useful. (RISC OS)

               Not supported. (Cygwin, Win32)

               Invokes VMS debugger. (VMS)

       exec    Does not automatically flush output handles on some platforms.
               (SunOS, Solaris, HP-UX)

               Not supported. (Symbian OS)

       exit    Emulates Unix exit() (which considers "exit 1" to indicate an
               error) by mapping the 1 to SS$_ABORT (44).  This behavior may
               be overridden with the pragma "use vmsish 'exit'".  As with the
               CRTL's exit() function, "exit 0" is also mapped to an exit
               status of SS$_NORMAL (1); this mapping cannot be overridden.
               Any other argument to exit() is used directly as Perl's exit
               status.  On VMS, unless the future POSIX_EXIT mode is enabled,
               the exit code should always be a valid VMS exit code and not a
               generic number.  When the POSIX_EXIT mode is enabled, a generic
               number will be encoded in a method compatible with the C
               library _POSIX_EXIT macro so that it can be decoded by other
               programs, particularly ones written in C, like the GNV package.

               "exit()" resets file pointers, which is a problem when called
               from a child process (created by "fork()") in "BEGIN".  A
               workaround is to use "POSIX::_exit".  (Solaris)

                   exit unless $Config{archname} =~ /\bsolaris\b/;
                   require POSIX and POSIX::_exit(0);

       fcntl   Not implemented. (Win32)

               Some functions available based on the version of VMS. (VMS)

       getpgrp Not implemented. (Win32, VMS, RISC OS)

       getppid Not implemented. (Win32, RISC OS)

               Not implemented. (Win32, VMS, RISC OS, VOS)

               Not implemented. (Win32)

               Not useful. (RISC OS)

               Not implemented. (Win32, VMS, RISC OS)

               Not implemented. (Win32, Plan 9)

               Not implemented. (Win32)

               Not useful. (RISC OS)

               Not implemented. (Win32, VMS, RISC OS)

               Not implemented. (Win32, Plan 9)

               Not implemented. (Win32)

               Not implemented. (Win32, VMS)

               "gethostbyname('localhost')" does not work everywhere: you may
               have to use "gethostbyname('')". (Irix 5)

               Not implemented. (Win32)

               Not implemented. (Win32, Plan 9)

               Not implemented. (Win32, Plan 9)

               Not implemented. (Win32, Plan 9)

               Not implemented. (Win32)

               Not implemented. (RISC OS, VMS, Win32)

               Not implemented. (Win32)

               Not implemented. (Win32, Plan 9)

               Not implemented. (Win32, Plan 9)

               Not implemented. (Plan 9, Win32)

       getsockopt SOCKET,LEVEL,OPTNAME
               Not implemented. (Plan 9)

       glob    This operator is implemented via the File::Glob extension on
               most platforms.  See File::Glob for portability information.

       gmtime  In theory, gmtime() is reliable from -2**63 to 2**63-1.
               However, because work arounds in the implementation use
               floating point numbers, it will become inaccurate as the time
               gets larger.  This is a bug and will be fixed in the future.

               On VOS, time values are 32-bit quantities.

               Not implemented. (VMS)

               Available only for socket handles, and it does what the
               ioctlsocket() call in the Winsock API does. (Win32)

               Available only for socket handles. (RISC OS)

       kill    Not implemented, hence not useful for taint checking. (RISC OS)

               "kill()" doesn't have the semantics of "raise()", i.e. it
               doesn't send a signal to the identified process like it does on
               Unix platforms.  Instead "kill($sig, $pid)" terminates the
               process identified by $pid, and makes it exit immediately with
               exit status $sig.  As in Unix, if $sig is 0 and the specified
               process exists, it returns true without actually terminating
               it. (Win32)

               "kill(-9, $pid)" will terminate the process specified by $pid
               and recursively all child processes owned by it.  This is
               different from the Unix semantics, where the signal will be
               delivered to all processes in the same process group as the
               process specified by $pid. (Win32)

               and the Perl process will need Administrator or Backup Operator
               privileges to create hard links.

               Available on 64 bit OpenVMS 8.2 and later.  (VMS)

               localtime() has the same range as "gmtime", but because time
               zone rules change its accuracy for historical and future times
               may degrade but usually by no more than an hour.

       lstat   Not implemented. (RISC OS)

               Return values (especially for device and inode) may be bogus.

       msgrcv  Not implemented. (Win32, VMS, Plan 9, RISC OS, VOS)

       open    open to "|-" and "-|" are unsupported. (Win32, RISC OS)

               Opening a process does not automatically flush output handles
               on some platforms.  (SunOS, Solaris, HP-UX)

               Not implemented. (Win32, VMS, RISC OS)

       rename  Can't move directories between directories on different logical
               volumes. (Win32)

               Will not cause readdir() to re-read the directory stream.  The
               entries already read before the rewinddir() call will just be
               returned again from a cache buffer. (Win32)

       select  Only implemented on sockets. (Win32, VMS)

               Only reliable on sockets. (RISC OS)

               Note that the "select FILEHANDLE" form is generally portable.

       semop   Not implemented. (Win32, VMS, RISC OS)

               Not implemented. (VMS, Win32, RISC OS)

       setpgrp Not implemented. (Win32, VMS, RISC OS, VOS)

               Not implemented. (Win32, VMS, RISC OS, VOS)

       sleep   Emulated using synchronization functions such that it can be
               interrupted by alarm(), and limited to a maximum of 4294967
               seconds, approximately 49 days. (Win32)

               A relatively recent addition to socket functions, may not be
               implemented even in Unix platforms.

               Not implemented. (RISC OS)

               Available on 64 bit OpenVMS 8.2 and later.  (VMS)

       stat    Platforms that do not have rdev, blksize, or blocks will return
               these as '', so numeric comparison or manipulation of these
               fields may cause 'not numeric' warnings.

               ctime not supported on UFS (Mac OS X).

               ctime is creation time instead of inode change time  (Win32).

               device and inode are not meaningful.  (Win32)

               device and inode are not necessarily reliable.  (VMS)

               mtime, atime and ctime all return the last modification time.
               Device and inode are not necessarily reliable.  (RISC OS)

               dev, rdev, blksize, and blocks are not available.  inode is not
               meaningful and will differ between stat calls on the same file.

               some versions of cygwin when doing a stat("foo") and if not
               finding it may then attempt to stat("foo.exe") (Cygwin)

               On Win32 stat() needs to open the file to determine the link
               count and update attributes that may have been changed through
               hard links.  Setting ${^WIN32_SLOPPY_STAT} to a true value
               speeds up stat() by not performing this operation. (Win32)

       symlink Not implemented. (Win32, RISC OS)

               Implemented on 64 bit VMS 8.3.  VMS requires the symbolic link
               to be in Unix syntax if it is intended to resolve to a valid

       syscall Not implemented. (Win32, VMS, RISC OS, VOS)

       sysopen The traditional "0", "1", and "2" MODEs are implemented with
               different numeric values on some systems.  The flags exported
               by "Fcntl" (O_RDONLY, O_WRONLY, O_RDWR) should work everywhere
               though.  (Mac OS, OS/390)

       system  As an optimization, may not call the command shell specified in
               performed (if at all) by the run time library of the spawned
               program.  "system" list will call the Unix emulation library's
               "exec" emulation, which attempts to provide emulation of the
               stdin, stdout, stderr in force in the parent, providing the
               child program uses a compatible version of the emulation
               library.  scalar will call the native command line direct and
               no such emulation of a child Unix program will exists.  Mileage
               will vary.  (RISC OS)

               Does not automatically flush output handles on some platforms.
               (SunOS, Solaris, HP-UX)

               The return value is POSIX-like (shifted up by 8 bits), which
               only allows room for a made-up value derived from the severity
               bits of the native 32-bit condition code (unless overridden by
               "use vmsish 'status'").  If the native condition code is one
               that has a POSIX value encoded, the POSIX value will be decoded
               to extract the expected exit value.  For more details see "$?"
               in perlvms. (VMS)

       times   "cumulative" times will be bogus.  On anything other than
               Windows NT or Windows 2000, "system" time will be bogus, and
               "user" time is actually the time returned by the clock()
               function in the C runtime library. (Win32)

               Not useful. (RISC OS)

               Not implemented. (Older versions of VMS)

               Truncation to same-or-shorter lengths only. (VOS)

               If a FILEHANDLE is supplied, it must be writable and opened in
               append mode (i.e., use "open(FH, '>>filename')" or
               "sysopen(FH,...,O_APPEND|O_RDWR)".  If a filename is supplied,
               it should not be held open elsewhere. (Win32)

       umask   Returns undef where unavailable.

               "umask" works but the correct permissions are set only when the
               file is finally closed. (AmigaOS)

       utime   Only the modification time is updated. (VMS, RISC OS)

               May not behave as expected.  Behavior depends on the C runtime
               library's implementation of utime(), and the filesystem being
               used.  The FAT filesystem typically does not support an "access
               time" field, and it may limit timestamps to a granularity of
               two seconds. (Win32)

       waitpid Can only be applied to process handles returned for processes
               spawned using "system(1, ...)" or pseudo processes created with
               "fork()". (Win32)

           Windows 2000
           Windows XP
           Windows Server 2003
           Windows Vista
           Windows Server 2008
           Windows 7
       Solaris (x86, SPARC)
           Alpha (7.2 and later)
           I64 (8.2 and later)
       Debian GNU/kFreeBSD
       Irix (6.5. What else?)
       Dragonfly BSD
       Midnight BSD
       QNX Neutrino RTOS (6.5.0)
       MirOS BSD
       Stratus OpenVOS (17.0 or later)

           time_t issues that may or may not be fixed
       Symbian (Series 60 v3, 3.2 and 5 - what else?)
       Stratus VOS / OpenVOS

EOL Platforms (Perl 5.14)
       The following platforms were supported by a previous version of Perl
       but have been officially removed from Perl's source code as of 5.12:

       Atari MiNT
       Apollo Domain/OS
       Apple Mac OS 8/9
       Tenon Machten

       The following platforms were supported up to 5.10.  They may still have
       worked in 5.12, but supporting code has been removed for 5.14:

       Windows 95
       Windows 98
       Windows ME
       Windows NT4

Supported Platforms (Perl 5.8)
       As of July 2002 (the Perl release 5.8.0), the following platforms were
       able to build Perl from the standard source code distribution available
       at <>

               Mac OS X        (Darwin)
               ReliantUNIX     (formerly SINIX)
               OpenVMS         (formerly VMS)
               Open UNIX       (Unixware) (since Perl 5.8.1/5.9.0)
               OS/400          (using the PASE) (since Perl 5.8.1/5.9.0)
               POSIX-BC        (formerly BS2000)
               SunOS 4
               SUPER-UX        (NEC)
               Tru64 UNIX      (formerly DEC OSF/1, Digital UNIX)
               VOS / OpenVOS
               Win95/98/ME/2K/XP 2)
               z/OS            (formerly OS/390)

               1) in DOS mode either the DOS or OS/2 ports can be used
               2) compilers: Borland, MinGW (GCC), VC6

       The following platforms worked with the previous releases (5.6 and
       5.7), but we did not manage either to fix or to test these in time for
       the 5.8.0 release.  There is a very good chance that many of these will
       work fine with the 5.8.0.

               SCO SV
               Windows 3.1

       Known to be broken for 5.8.0 (but 5.6.1 and 5.7.2 can be used):


       The following platforms have been known to build Perl from source in
       the past (5.005_03 and earlier), but we haven't been able to verify
       their status for the current release, either because the
       hardware/software platforms are rare or because we don't have an active
               MachTen 68k
               Plan 9
               SCO ODT/OSR
               Unisys Dynix

       The following platforms have their own source code distributions and
       binaries available via <>

                                       Perl release

               OS/400 (ILE)            5.005_02
               Tandem Guardian         5.004

       The following platforms have only binaries available via
       <> :

                                       Perl release

               Acorn RISCOS            5.005_02
               AOS                     5.002
               LynxOS                  5.004_02

       Although we do suggest that you always build your own Perl from the
       source code, both for maximal configurability and for security, in case
       you are in a hurry you can check <>
       for binary distributions.

       perlaix, perlamiga, perlbs2000, perlce, perlcygwin, perldgux, perldos,
       perlebcdic, perlfreebsd, perlhurd, perlhpux, perlirix, perlmacos,
       perlmacosx, perlnetware, perlos2, perlos390, perlos400, perlplan9,
       perlqnx, perlsolaris, perltru64, perlunicode, perlvms, perlvos,
       perlwin32, and Win32.

       Abigail <>, Charles Bailey <>,
       Graham Barr <>, Tom Christiansen <>,
       Nicholas Clark <>, Thomas Dorner <>,
       der Sanden <>, Gurusamy Sarathy
       <>, Paul J. Schinder <>, Michael
       G Schwern <>, Dan Sugalski <>, Nathan
       Torkington <>, John Malmberg <>

perl v5.18.2                      2014-01-06                       PERLPORT(1)
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