perlport


DESCRIPTION
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
them.

type of computer and taking advantage of a full range of them.
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

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">").

ISSUES
Newlines
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 wallet. 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 change: 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

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
characters.

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
filenames.

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

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;}

Networking
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
port.

Don't assume that you can reach yourself or any node by the name
'localhost'.  The same goes for '127.0.0.1'.  You will have to try
both.

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 portability. 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
Time::Local.

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.  $offset can then be added to a Unix time value to get what should be the proper value on any system. Character sets and character encoding Assume very little about character sets. Assume nothing about numerical values ("ord", "chr") of characters. Do not use explicit code point ranges (like \xHH-\xHH); use for example symbolic character classes like "[:print:]". Do not assume that the alphabetic characters are encoded contiguously (in the numeric sense). There may be gaps. Do not assume anything about the ordering of the characters. The lowercase letters may come before or after the uppercase letters; the lowercase and uppercase may be interlaced so that both "a" and "A" come before "b"; the accented and other international characters may be interlaced so that ae comes before "b". Internationalisation If you may assume POSIX (a rather large assumption), you may read more about the POSIX locale system from perllocale. The locale system at least attempts to make things a little bit more portable, or at least more convenient and native-friendly for non-English users. The system affects character sets and encoding, and date and time formatting--amongst other things. embedding the bytes as-is. If you want to write your code in UTF-8, you can use the "utf8". System Resources If your code is destined for systems with severely constrained (or missing!) virtual memory systems then you want to be especially mindful of avoiding wasteful constructs such as: my @lines = <$very_large_file>;            # bad

while (<$fh>) {$file .= $_} # sometimes bad my$file = join('', <$fh>); # better The last two constructs may appear unintuitive to most people. The first repeatedly grows a string, whereas the second allocates a large chunk of memory in one go. On some systems, the second is more efficient that the first. Security Most multi-user platforms provide basic levels of security, usually implemented at the filesystem level. Some, however, unfortunately do not. Thus the notion of user id, or "home" directory, or even the state of being logged-in, may be unrecognizable on many platforms. If you write programs that are security-conscious, it is usually best to know what type of system you will be running under so that you can write code explicitly for that platform (or class of platforms). Don't assume the Unix filesystem access semantics: the operating system or the filesystem may be using some ACL systems, which are richer languages than the usual rwx. Even if the rwx exist, their semantics might be different. (From security viewpoint testing for permissions before attempting to do something is silly anyway: if one tries this, there is potential for race conditions. Someone or something might change the permissions between the permissions check and the actual operation. Just try the operation.) Don't assume the Unix user and group semantics: especially, don't expect the$< and $> (or the$( and $)) to work for switching identities (or memberships). Don't assume set-uid and set-gid semantics. (And even if you do, think twice: set-uid and set-gid are a known can of security worms.) Style For those times when it is necessary to have platform-specific code, consider keeping the platform-specific code in one place, making porting to other platforms easier. Use the Config module and the special variable$^O to differentiate platforms, as described in
"PLATFORMS".

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
notations.

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: cpan-testers-discuss@perl.org

o   Testing results: <http://www.cpantesters.org/>

PLATFORMS
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.

Unix
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
"opendir".

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,
unfortunately.

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

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, <http://www.delorie.com/djgpp/> and
perldos.

o   The EMX environment for DOS, OS/2, etc. emx@iaehv.nl,
<ftp://hobbes.nmsu.edu/pub/os2/dev/emx/>  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, <http://www.activestate.com/>

o   The Cygwin environment for Win32; README.cygwin (installed as
perlcygwin), <http://www.cygwin.com/>

o   The U/WIN environment for Win32,
<http://www.research.att.com/sw/tools/uwin/>

o   Build instructions for OS/2, perlos2

VMS
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__"
#!/usr/bin/perl

print "Hello from Perl!\n";

__END__
$endif Do take care with "$ 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
internally.

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.

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.2.3.4.5.6.7.8]" is a valid directory specification but
"PERL_ROOT:[LIB.2.3.4.5.6.7.8.9]" 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   vmsperl list, vmsperl-subscribe@perl.org

o   vmsperl on the web, <http://www.sidhe.org/vmsperl/index.html>

VOS
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
following:

$perl -ne "print if /perl_setup/i" >system>notices$ 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"; die; } 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 <http://www.stratus.com> o VOS Open-Source Software on the web at <http://ftp.stratus.com/pub/vos/vos.html> 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 hello.pl in the root of the QOpenSys
file system.  On the AS/400 calls to "system" or backticks must use CL
syntax.

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        $Config{'archname'} -------------------------------------------- OS/390 os390 os390 OS400 os400 os400 POSIX-BC posix-bc BS2000-posix-bc Some simple tricks for determining if you are running on an EBCDIC platform could include any of the following (perhaps all): if ("\t" eq "\005") { print "EBCDIC may be spoken here!\n"; } if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; } if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; } One thing you may not want to rely on is the EBCDIC encoding of punctuation characters since these may differ from code page to code page (and once your module or script is rumoured to work with EBCDIC, folks will want it to work with all EBCDIC character sets). Also see: o perlos390, README.os390, perlbs2000, perlebcdic. o The perl-mvs@perl.org list is for discussion of porting issues as well as general usage issues for all EBCDIC Perls. Send a message body of "subscribe perl-mvs" to majordomo@perl.org. o AS/400 Perl information at <http://as400.rochester.ibm.com/> as well as on CPAN in the ports/ directory. Acorn RISC OS Because Acorns use ASCII with newlines ("\n") in text files as "\012" like Unix, and because Unix filename emulation is turned on by default, where Special_Field is not usually present, but may contain . and$ .
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$Dir'} . 'Modules'". The obvious implication of this is that fully qualified filenames can start with "<>" and should be protected when "open" is used for input. Because "." was in use as a directory separator and filenames could not be assumed to be unique after 10 characters, Acorn implemented the C compiler to strip the trailing ".c" ".h" ".s" and ".o" suffix from filenames specified in source code and store the respective files in subdirectories named after the suffix. Hence files are translated: foo.h h.foo C:foo.h C:h.foo (logical path variable) sys/os.h sys.h.os (C compiler groks Unix-speak) 10charname.c c.10charname 10charname.o o.10charname 11charname_.c c.11charname (assuming filesystem truncates at 10) The Unix emulation library's translation of filenames to native assumes that this sort of translation is required, and it allows a user-defined list of known suffixes that it will transpose in this fashion. This may seem transparent, but consider that with these rules foo/bar/baz.h and foo/bar/h/baz both map to foo.bar.h.baz, and that "readdir" and "glob" cannot and do not attempt to emulate the reverse mapping. Other "."'s in filenames are translated to "/". As implied above, the environment accessed through %ENV is global, and the convention is that program specific environment variables are of the form "Program$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
$^O is "riscos" (because we don't like shouting). Other perls Perl has been ported to many platforms that do not fit into any of the categories listed above. Some, such as AmigaOS, QNX, Plan 9, and VOS, have been well-integrated into the standard Perl source code kit. You may need to see the ports/ directory on CPAN for information, and possibly binaries, for the likes of: aos, Atari ST, lynxos, riscos, Novell Netware, Tandem Guardian, etc. (Yes, we know that some of these OSes may fall under the Unix category, but we are not a standards body.) Some approximate operating system names and their$^O values in the
"OTHER" category include:

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

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
<http://www.novell.com/> as well as from CPAN.

FUNCTION IMPLEMENTATIONS
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
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
at
<http://www.opengroup.org/onlinepubs/009695399/functions/atan2.html>.

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)

dbmclose
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.
(VMS)

"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) getpriority Not implemented. (Win32, VMS, RISC OS, VOS) getpwnam Not implemented. (Win32) Not useful. (RISC OS) getgrnam Not implemented. (Win32, VMS, RISC OS) getnetbyname Not implemented. (Win32, Plan 9) getpwuid Not implemented. (Win32) Not useful. (RISC OS) getgrgid Not implemented. (Win32, VMS, RISC OS) getnetbyaddr Not implemented. (Win32, Plan 9) getprotobynumber getservbyport getpwent Not implemented. (Win32) getgrent Not implemented. (Win32, VMS) gethostbyname "gethostbyname('localhost')" does not work everywhere: you may have to use "gethostbyname('127.0.0.1')". (Irix 5) gethostent Not implemented. (Win32) getnetent Not implemented. (Win32, Plan 9) getprotoent Not implemented. (Win32, Plan 9) getservent Not implemented. (Win32, Plan 9) sethostent Not implemented. (Win32) endgrent Not implemented. (RISC OS, VMS, Win32) endhostent Not implemented. (Win32) endnetent Not implemented. (Win32, Plan 9) endprotoent Not implemented. (Win32, Plan 9) endservent 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. ioctl FILEHANDLE,FUNCTION,SCALAR 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 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. (Win32) msgctl msgget msgsnd 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) readlink Not implemented. (Win32, VMS, RISC OS) rename Can't move directories between directories on different logical volumes. (Win32) rewinddir 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. semctl semget semop Not implemented. (Win32, VMS, RISC OS) setgrent Not implemented. (VMS, Win32, RISC OS) setpgrp Not implemented. (Win32, VMS, RISC OS, VOS) setpriority 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) sockatmark A relatively recent addition to socket functions, may not be implemented even in Unix platforms. socketpair 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. (os2) 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
path.

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)

truncate
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" 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)

wait
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
Cygwin
Solaris (x86, SPARC)
OpenVMS
Alpha (7.2 and later)
I64 (8.2 and later)
Symbian
NetBSD
FreeBSD
Debian GNU/kFreeBSD
Haiku
Irix (6.5. What else?)
OpenBSD
Dragonfly BSD
Midnight BSD
QNX Neutrino RTOS (6.5.0)
MirOS BSD
Stratus OpenVOS (17.0 or later)
Caveats:

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

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 <http://www.cpan.org/src/>

AIX
BeOS
Mac OS X        (Darwin)
MPE/iX
NetBSD
NetWare
NonStop-UX
ReliantUNIX     (formerly SINIX)
OpenBSD
OpenVMS         (formerly VMS)
Open UNIX       (Unixware) (since Perl 5.8.1/5.9.0)
OS/2
OS/400          (using the PASE) (since Perl 5.8.1/5.9.0)
PowerUX
POSIX-BC        (formerly BS2000)
QNX
Solaris
SunOS 4
SUPER-UX        (NEC)
Tru64 UNIX      (formerly DEC OSF/1, Digital UNIX)
UNICOS
UNICOS/mk
UTS
VOS / OpenVOS
Win95/98/ME/2K/XP 2)
WinCE
z/OS            (formerly OS/390)
VM/ESA

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.

BSD/OS
DomainOS
Hurd
LynxOS
MachTen
PowerMAX
SCO SV
SVR4
Unixware
Windows 3.1

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

AmigaOS

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
ESIX
FPS
GENIX
Greenhills
ISC
MachTen 68k
MPC
NEWS-OS
NextSTEP
OpenSTEP
Opus
Plan 9
RISC/os
SCO ODT/OSR
Stellar
SVR2
TI1500
TitanOS
Ultrix
Unisys Dynix

The following platforms have their own source code distributions and
binaries available via <http://www.cpan.org/ports/>

Perl release

OS/400 (ILE)            5.005_02
Tandem Guardian         5.004

The following platforms have only binaries available via
<http://www.cpan.org/ports/index.html> :

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 <http://www.cpan.org/ports/index.html>
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.

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