PERLPORT(1) Perl Programmers Reference Guide PERLPORT(1)
NAME
perlport - Writing portable Perl
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.
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 has 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.
When the code will run on only two or three operating systems, you may
need to consider only the differences of those particular systems. The
important thing is to decide where the code will run and to be
deliberate in your decision.
The material below is separated into three main sections: main issues of
portability ("ISSUES"), platform-specific issues ("PLATFORMS"), and
built-in Perl functions that behave differently on various ports
("FUNCTION IMPLEMENTATIONS").
This information should not be considered complete; it includes 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",
Mac OS uses "\015", and z/OS uses "\025".
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". On EBCDIC platforms, "\n" could be "\025" or "\045". 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 safely.
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 $/ is "\n", but robust socket code will recognize as either
"\012" or "\015\012" as end of line:
while (<$socket>) { # NOT ADVISABLE!
# ...
}
Because both CRLF and LF end in LF, the input record separator can be
set to LF and any CR stripped later. Better to write:
use Socket qw(:DEFAULT :crlf);
local($/) = LF; # not needed if $/ is already \012
while (<$socket>) {
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 |
----------------------
* text-mode STDIO
Numbers endianness and Width
Different CPUs store integers and floating point numbers in different
orders (called endianness) and widths (32-bit and 64-bit being the most
common today). This affects your programs when they attempt to transfer
numbers in binary format from one CPU architecture to another, usually
either "live" via network connection, or by storing the numbers to
secondary storage such as a disk file or tape.
Conflicting storage orders make an utter mess out of the numbers. If a
little-endian host (Intel, VAX) stores 0x12345678 (305419896 in
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.
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:).
Mac OS 9 and earlier used ":" as a path separator instead of "/".
The filesystem may support neither hard links ("link") nor symbolic
links ("symlink", "readlink", "lstat").
The filesystem may support neither access timestamp nor change timestamp
(meaning that about the only portable timestamp is the modification
timestamp), or one second granularity of any timestamps (e.g. the FAT
filesystem limits the time granularity to two seconds).
The "inode change timestamp" (the "-C" filetest) may really be the
"creation timestamp" (which it is not in Unix).
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.
The "File::Spec" modules provide methods to manipulate path
specifications and return the results in native format for each
platform. This is often unnecessary as Unix-style paths are understood
by Perl on every supported platform, but if you need to produce native
paths for a native utility that does not understand Unix syntax, or if
you are operating on paths or path components in unknown (and thus
possibly native) syntax, "File::Spec" is your friend. Here are two
brief examples:
use File::Spec::Functions;
chdir(updir()); # go up one directory
# Concatenate a path from its components
my $file = catfile(updir(), 'temp', 'file.txt');
# on Unix: '../temp/file.txt'
# on Win32: '..\temp\file.txt'
# on VMS: '[-.temp]file.txt'
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 to
override the default location of the file.
Don't assume a text file will end with a newline. They should, but
people forget.
Do not have two files or directories of the same name with different
case, like test.pl and Test.pl, as many platforms have case-insensitive
(or at least case-forgiving) filenames. Also, try not to have non-word
characters (except for ".") in the names, and keep them to the 8.3
convention, for maximum portability, onerous a burden though this may
appear.
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
the three-arg version of "open":
open my $fh, '<', $existing_file) or die $!;
Two-arg "open" is magic and can translate characters like ">", "<", and
"|" in filenames, which is usually the wrong thing to do. "sysopen" and
three-arg "open" don't have this problem.
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 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 s 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 S T U V W X Y Z
0 1 2 3 4 5 6 7 8 9
. _ -
and "-" 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.)
On Windows extra "."s at the end of a file or directory name are ignored
in most circumstances, and a directory name containing only three or
more "."s are treated as the current directory by some APIs.
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
with, so don't stay up late worrying about it.
Some platforms can't delete or rename files held open by the system,
this limitation may also apply to changing filesystem metainformation
like file permissions or owners. Remember to "close" files when you are
done with them. Don't "unlink" or "rename" an open file. Don't "tie"
or "open" a file already tied or opened; "untie" or "close" it first.
Don't open the same file more than once at a time for writing, as some
operating systems put mandatory locks on such files.
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 undeletable 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{PATH}, 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 are documented.
On VMS by default, changes to the %ENV hash persist after perl exits.
Subsequent invocations of perl in the same process can inadvertently
inherit environment settings that were meant to be temporary.
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
string 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. First,
many systems have "internal" commands that are built-in to the shell or
OS and while these commands can be invoked, there is no corresponding
file. Second, some operating systems (e.g., Cygwin, OS/2, and VOS) have
required suffixes for executable files; these suffixes are generally
permitted on the command name but are not required. Thus, a command
like "perl" might exist in a file named perl, perl.exe, or perl.pm,
depending on the operating system. The variable $Config{_exe} in the
"Config" module holds the executable suffix, if any. Third, the VMS
port carefully sets up $^X and $Config{perlpath} so that no further
processing is required. This is just as well, because the matching
regular expression used below would then have to deal with a possible
trailing version number in the VMS 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 $thisperl =~ m/\Q$Config{_exe}\E$/i;
}
To convert $Config{perlpath} to a file pathname, say:
use Config;
my $thisperl = $Config{perlpath};
if ($^O ne 'VMS') {
$thisperl .= $Config{_exe}
unless $thisperl =~ m/\Q$Config{_exe}\E$/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'ts 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.
Interprocess Communication (IPC)
In general, don't directly access the system in code meant to be
portable. That means, no "system", "exec", "fork", "pipe", `` or
"qx//", "open" with a "|", nor any of the other things that makes being
a Perl hacker worth being.
Commands that launch external processes are generally supported on most
platforms (though many of them do not support any type of forking). The
problem with using them arises from what you invoke them on. External
tools are often named differently on different platforms, may not be
available in the same location, might accept different arguments, can
behave differently, and often present their results in a 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(my $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" module, 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 exposes 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
the others are generally available on all Unix and DOSish ports, but not
in MacPerl, where only "NDBM_File" and "DB_File" are available.
The good news is that at least some DBM module should be available, and
"AnyDBM_File" will use whichever module it can find. Of course, then
the code needs to be fairly strict, dropping to the greatest common
factor (e.g., not exceeding 1K for each record), so that it will work
with any DBM module. See AnyDBM_File for more details.
Time and Date
The system's notion of time of day and calendar date is controlled in
widely different ways. Don't assume the timezone is stored in $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 "Time::Piece"
(see "Date Parsing" in Time::Piece) or "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.
use Time::Local qw(timegm);
my $offset = timegm(0, 0, 0, 1, 0, 1970);
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)". However,
starting in Perl v5.22, regular expression pattern bracketed character
class ranges specified like "qr/[\N{U+HH}-\N{U+HH}]/" are portable, and
starting in Perl v5.24, the same ranges are portable in "tr///". You
can portably use symbolic character classes like "[:print:]".
Do not assume that the alphabetic characters are encoded contiguously
(in the numeric sense). There may be gaps. Special coding in Perl,
however, guarantees that all subsets of "qr/[A-Z]/", "qr/[a-z]/", and
"qr/[0-9]/" behave as expected. "tr///" behaves the same for these
ranges. In patterns, any ranges specified with end points using the
"\N{...}" notations ensures character set portability, but it is a bug
in Perl v5.22 that this isn't true of "tr///", fixed in v5.24.
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 ä comes before "b". Unicode::Collate can be used to
sort this all out.
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.
If you really want to be international, you should consider Unicode.
See perluniintro and perlunicode for more information.
By default Perl assumes your source code is written in an 8-bit ASCII
superset. To embed Unicode characters in your strings and regexes, you
can use the "\x{HH}" or (more portably) "\N{U+HH}" notations. You can
also use the "utf8" pragma and write your code in UTF-8, which lets you
use Unicode characters directly (not just in quoted constructs but also
in identifiers).
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 than 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 the 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
$< and $> (or $( 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 $^O to differentiate platforms, as described in "PLATFORMS".
Beware of the "else syndrome":
if ($^O eq 'MSWin32') {
# code that assumes Windows
} else {
# code that assumes Linux
}
The "else" branch should be used for the really ultimate fallback, not
for code specific to some platform.
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 often
happens when tests spawn off other processes or call external programs
to aid in the testing, or when (as noted above) the tests assume certain
things about the filesystem and paths. Be careful not to depend on a
specific output style for errors, such as when checking $! after a
failed system call. Using $! for anything else than displaying it as
output is doubtful (though see the "Errno" module for testing reasonably
portably for error value). Some platforms expect a certain output
format, and Perl on those platforms may have been adjusted accordingly.
Most specifically, don't anchor a regex when testing an error value.
CPAN Testers
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:
• Mailing list: cpan-testers-discuss@perl.org
• Testing results: <https://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
DYNIX/ptx dynixptx i386-dynixptx
FreeBSD freebsd freebsd-i386
Haiku haiku BePC-haiku
Linux linux arm-linux
Linux linux armv5tel-linux
Linux linux i386-linux
Linux linux i586-linux
Linux linux ppc-linux
HP-UX hpux PA-RISC1.1
IRIX irix irix
Mac OS X darwin darwin
NeXT 3 next next-fat
NeXT 4 next OPENSTEP-Mach
openbsd openbsd i386-openbsd
OSF1 dec_osf alpha-dec_osf
reliantunix-n svr4 RM400-svr4
SCO_SV sco_sv i386-sco_sv
SINIX-N svr4 RM400-svr4
sn4609 unicos CRAY_C90-unicos
sn6521 unicosmk t3e-unicosmk
sn9617 unicos CRAY_J90-unicos
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 $filespec3 = 'c:\\foo\\bar\\file.txt';
System calls accept either "/" or "\" as the path separator. However,
many command-line utilities of DOS vintage treat "/" as the option
prefix, so may get confused by filenames containing "/". Aside from
calling any external programs, "/" will work just fine, and probably
better, as it is more consistent with popular usage, and avoids the
problem of remembering what to backwhack and what not to.
The DOS FAT filesystem can accommodate only "8.3" style filenames.
Under the "case-insensitive, but case-preserving" HPFS (OS/2) and NTFS
(NT) filesystems you may have to be careful about case returned with
functions like "readdir" or used with functions like "open" or
"opendir".
DOS also treats several filenames as special, such as AUX, PRN, NUL,
CON, COM1, LPT1, LPT2, etc. Unfortunately, sometimes these filenames
won't even work if you include an explicit directory prefix. It is best
to avoid such filenames, if you want your code to be portable to DOS and
its derivatives. It's hard to know what these all are, unfortunately.
Users of these operating systems may also wish to make use of scripts
such as pl2bat.bat to put wrappers around your scripts.
Newline ("\n") is translated as "\015\012" by the I/O system when
reading from and writing to files (see "Newlines").
binmode($filehandle) will keep "\n" translated as "\012" for that
filehandle. "binmode" should always be used for 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 $Config{archname} ID Version
---------------------------------------------------------
MS-DOS dos ?
PC-DOS dos ?
OS/2 os2 ?
Windows 3.1 ? ? 0 3 01
Windows 95 MSWin32 MSWin32-x86 1 4 00
Windows 98 MSWin32 MSWin32-x86 1 4 10
Windows ME MSWin32 MSWin32-x86 1 ?
Windows NT MSWin32 MSWin32-x86 2 4 xx
Windows NT MSWin32 MSWin32-ALPHA 2 4 xx
Windows NT MSWin32 MSWin32-ppc 2 4 xx
Windows 2000 MSWin32 MSWin32-x86 2 5 00
Windows XP MSWin32 MSWin32-x86 2 5 01
Windows 2003 MSWin32 MSWin32-x86 2 5 02
Windows Vista MSWin32 MSWin32-x86 2 6 00
Windows 7 MSWin32 MSWin32-x86 2 6 01
Windows 7 MSWin32 MSWin32-x64 2 6 01
Windows 2008 MSWin32 MSWin32-x86 2 6 01
Windows 2008 MSWin32 MSWin32-x64 2 6 01
Windows CE MSWin32 ? 3
Cygwin cygwin cygwin
The various MSWin32 Perl's can distinguish the OS they are running on
via the value of the fifth element of the list returned from
Win32::GetOSVersion(). For example:
if ($^O eq 'MSWin32') {
my @os_version_info = Win32::GetOSVersion();
print +('3.1','95','NT')[$os_version_info[4]],"\n";
}
There are also "Win32::IsWinNT()|Win32/Win32::IsWinNT()",
"Win32::IsWin95()|Win32/Win32::IsWin95()", and Win32::GetOSName(); try
"perldoc Win32". 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
Errors set by Winsock functions are now put directly into $^E, and the
relevant "WSAE*" error codes are now exported from the Errno and POSIX
modules for testing this against.
The previous behavior of putting the errors (converted to POSIX-style
"E*" error codes since Perl 5.20.0) into $! was buggy due to the non-
equivalence of like-named Winsock and POSIX error constants, a
relationship between which has unfortunately been established in one way
or another since Perl 5.8.0.
The new behavior provides a much more robust solution for checking
Winsock errors in portable software without accidentally matching POSIX
tests that were intended for other OSes and may have different meanings
for Winsock.
The old behavior is currently retained, warts and all, for backwards
compatibility, but users are encouraged to change any code that tests $!
against "E*" constants for Winsock errors to instead test $^E against
"WSAE*" constants. After a suitable deprecation period, which started
with Perl 5.24, the old behavior may be removed, leaving $! unchanged
after Winsock function calls, to avoid any possible confusion over which
error variable to check.
Also see:
• The EMX environment for DOS, OS/2, etc. emx@iaehv.nl,
<ftp://hobbes.nmsu.edu/pub/os2/dev/emx/> Also perlos2.
• Build instructions for Win32 in perlwin32, or under the Cygnus
environment in perlcygwin.
• The "Win32::*" modules in Win32.
• The ActiveState Pages, <https://www.activestate.com/>
• The Cygwin environment for Win32; README.cygwin (installed as
perlcygwin), <https://www.cygwin.com/>
• 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, designated by their on-
disk structure (ODS) level: ODS-2 and its successor ODS-5. The initial
port of Perl to VMS pre-dates ODS-5, but all current testing and
development assumes ODS-5 and its capabilities, including case
preservation, extended characters in filespecs, and names up to 8192
bytes long.
Perl on VMS can accept either VMS- or Unix-style file specifications as
in either of the following:
$ perl -ne "print if /perl_setup/i" SYS$LOGIN:LOGIN.COM
$ perl -ne "print if /perl_setup/i" /sys$login/login.com
but not a mixture of both as in:
$ perl -ne "print if /perl_setup/i" sys$login:/login.com
Can't open sys$login:/login.com: file specification syntax error
In general, the easiest path to portability is always to specify
filenames in Unix format unless they will need to be processed by native
commands or utilities. Because of this latter consideration, the
File::Spec module by default returns native format specifications
regardless of input format. This default may be reversed so that
filenames are always reported in Unix format by specifying the
"DECC$FILENAME_UNIX_REPORT" feature logical in the environment.
The file type, or extension, is always present in a VMS-format file
specification even if it's zero-length. This means that, by default,
"readdir" will return a trailing dot on a file with no extension, so
where you would see "a" on Unix you'll see "a." on VMS. However, the
trailing dot may be suppressed by enabling the
"DECC$READDIR_DROPDOTNOTYPE" feature in the environment (see the CRTL
documentation on feature logical names).
What "\n" represents depends on the type of file opened. It usually
represents "\012" but it could also be "\015", "\012", "\015\012",
"\000", "\040", or nothing depending on the file organization and record
format. The "VMS::Stdio" module provides access to the special fopen()
requirements of files with unusual attributes on VMS.
The value of $^O on OpenVMS is "VMS". To determine the architecture
that you are running on refer to $Config{archname}.
On VMS, perl determines the UTC offset from the
"SYS$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:
• README.vms (installed as README_vms), perlvms
• vmsperl list, vmsperl-subscribe@perl.org
• vmsperl on the web, <http://www.sidhe.org/vmsperl/index.html>
• VMS Software Inc. web site, <http://www.vmssoftware.com>
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 " " (space) or any
character from the set "!#%&'()*;<=>?".
Newer releases of VOS (OpenVOS Release 17.0 or later) support a feature
known as extended names. On these releases, file names can contain up
to 255 characters, are prohibited from starting with a "-" character,
and the set of prohibited characters is reduced to "#%*<>?". There are
restrictions involving spaces and apostrophes: these characters must
not begin or end a name, nor can they immediately precede or follow a
period. Additionally, a space must not immediately precede another
space or hyphen. Specifically, the following character combinations are
prohibited: space-space, space-hyphen, period-space, space-period,
period-apostrophe, 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 refer to $Config{archname}.
Also see:
• README.vos (installed as perlvos)
• 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.
• Stratus Technologies on the web at <http://www.stratus.com>
• VOS Open-Source Software on the web at
<http://ftp.stratus.com/pub/vos/vos.html>
EBCDIC Platforms
v5.22 core Perl runs on z/OS (formerly OS/390). Theoretically it could
run on the successors of OS/400 on AS/400 minicomputers as well as
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).
The rest of this section may need updating, but we don't know what it
should say. Please submit comments to
<https://github.com/Perl/perl5/issues>.
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
print "Hello from perl!\n";
OS/390 will support the "#!" shebang trick in release 2.8 and beyond.
Calls to "system" and backticks can use POSIX shell syntax on all S/390
systems.
On the AS/400, if PERL5 is in your library list, you may need to wrap
your Perl scripts in a CL procedure to invoke them like so:
BEGIN
CALL PGM(PERL5/PERL) PARM('/QOpenSys/hello.pl')
ENDPGM
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 z/OS):
print "Content-type: text/html\r\n\r\n";
The values of $^O on some of these platforms include:
uname $^O $Config{archname}
--------------------------------------------
OS/390 os390 os390
OS400 os400 os400
POSIX-BC posix-bc BS2000-posix-bc
Some simple tricks for determining if you are running on an EBCDIC
platform could include any of the following (perhaps all):
if ("\t" eq "\005") { print "EBCDIC may be spoken here!\n"; }
if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; }
if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; }
One thing you may not want to rely on is the EBCDIC encoding of
punctuation characters since these may differ from code page to code
page (and once your module or script is rumoured to work with EBCDIC,
folks will want it to work with all EBCDIC character sets).
Also see:
• perlos390, perlos400, perlbs2000, perlebcdic.
• The perl-mvs@perl.org list is for discussion of porting issues as
well as general usage issues for all EBCDIC Perls. Send a message
body of "subscribe perl-mvs" to majordomo@perl.org.
• AS/400 Perl information at <http://as400.rochester.ibm.com/> as well
as on CPAN in the ports/ directory.
Acorn RISC OS
Because Acorns use ASCII with newlines ("\n") in text files as "\012"
like Unix, and because Unix filename emulation is turned on by default,
most simple scripts will probably work "out of the box". The native
filesystem is modular, and individual filesystems are free to be case-
sensitive or insensitive, and are usually case-preserving. Some native
filesystems have name length limits, which file and directory names are
silently truncated to fit. Scripts should be aware that the standard
filesystem currently has a name length limit of 10 characters, with up
to 77 items in a directory, but other filesystems may not impose such
limitations.
Native filenames are of the form
Filesystem#Special_Field::DiskName.$.Directory.Directory.File
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|/.|./|", swapping dots
and slashes.
Note that ""ADFS::HardDisk.$.File" ne 'ADFS::HardDisk.$.File'" and that
the second stage of "$" interpolation in regular expressions will fall
foul of the $. variable if scripts are not careful.
Logical paths specified by system variables containing comma-separated
search lists are also allowed; hence "System:Modules" is a valid
filename, and the filesystem will prefix "Modules" with each section of
"System$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 the three-
argument form of "open" should always be used.
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$Name". Each filesystem maintains a current directory, and
the current filesystem's current directory is the global current
directory. Consequently, sociable programs don't change the current
directory but rely on full pathnames, and programs (and Makefiles)
cannot assume that they can spawn a child process which can change the
current directory without affecting its parent (and everyone else for
that matter).
Because native operating system filehandles are global and are currently
allocated down from 255, with 0 being a reserved value, the Unix
emulation library emulates Unix filehandles. Consequently, you can't
rely on passing "STDIN", "STDOUT", or "STDERR" to your children.
The desire of users to express filenames of the form "<Foo$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
See also:
• Amiga, README.amiga (installed as perlamiga).
• Plan 9, README.plan9
FUNCTION IMPLEMENTATIONS
Listed below are functions that are either completely unimplemented or
else have been implemented differently on various platforms. Preceding
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
doubt, consult the platform-specific README files in the Perl source
distribution, and any other documentation resources accompanying a given
port.
Be aware, moreover, that even among Unix-ish systems there are
variations.
For many functions, you can also query %Config, exported by default from
the "Config" module. For example, to check whether the platform has the
"lstat" call, check $Config{d_lstat}. See Config for a full description
of available variables.
Alphabetical Listing of Perl Functions
-X (Win32) "-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).
(VMS) "-r", "-w", "-x", and "-o" tell whether the file is
accessible, which may not reflect UIC-based file protections.
(RISC OS) "-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.
(Win32, VMS, RISC OS) "-R", "-W", "-X", "-O" are
indistinguishable from "-r", "-w", "-x", "-o".
(Win32, VMS, RISC OS) "-g", "-k", "-u", "-A" are not
particularly meaningful.
(VMS, RISC OS) "-l" is not particularly meaningful.
(Win32) "-l" returns true for both symlinks and directory
junctions.
(VMS, RISC OS) "-p" is not particularly meaningful.
(VMS) "-d" is true if passed a device spec without an explicit
directory.
(Win32) "-x" (or "-X") determine if a file ends in one of the
executable suffixes.
(RISC OS) "-x" (or "-X") determine if a file has an executable
file type.
alarm (Win32) Emulated using timers that must be explicitly polled
whenever Perl wants to dispatch "safe signals" and therefore
cannot interrupt blocking system calls.
atan2 (Tru64, HP-UX 10.20) 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.
The current version of the standards for "atan2" is available at
<http://www.opengroup.org/onlinepubs/009695399/functions/atan2.html>.
binmode (RISC OS) Meaningless.
(VMS) Reopens file and restores pointer; if function fails,
underlying filehandle may be closed, or pointer may be in a
different position.
(Win32) The value returned by "tell" may be affected after the
call, and the filehandle may be flushed.
chdir (Win32) The current directory reported by the system may include
any symbolic links specified to chdir().
chmod (Win32) Only good for changing "owner" read-write access;
"group" and "other" bits are meaningless.
(RISC OS) Only good for changing "owner" and "other" read-write
access.
(VOS) Access permissions are mapped onto VOS access-control list
changes.
(Cygwin) The actual permissions set depend on the value of the
"CYGWIN" variable in the SYSTEM environment settings.
(Android) Setting the exec bit on some locations (generally
/sdcard) will return true but not actually set the bit.
(VMS) A mode argument of zero sets permissions to the user's
default permission mask rather than disabling all permissions.
chown (Plan 9, RISC OS) Not implemented.
(Win32) Does nothing, but won't fail.
(VOS) A little funky, because VOS's notion of ownership is a
little funky.
chroot (Win32, VMS, Plan 9, RISC OS, VOS) Not implemented.
crypt (Win32) May not be available if library or source was not
provided when building perl.
(Android) Not implemented.
dbmclose
(VMS, Plan 9, VOS) Not implemented.
dbmopen (VMS, Plan 9, VOS) Not implemented.
dump (RISC OS) Not useful.
(Cygwin, Win32) Not supported.
(VMS) Invokes VMS debugger.
exec (Win32) "exec LIST" without the use of indirect object syntax
("exec PROGRAM LIST") may fall back to trying the shell if the
first spawn() fails.
Note that the list form of exec() is emulated since the Win32
API CreateProcess() accepts a simple string rather than an array
of command-line arguments. This may have security implications
for your code.
(SunOS, Solaris, HP-UX) Does not automatically flush output
handles on some platforms.
exit (VMS) 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.
(Solaris) "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".
exit unless $Config{archname} =~ /\bsolaris\b/;
require POSIX;
POSIX::_exit(0);
fcntl (Win32) Not implemented.
(VMS) Some functions available based on the version of VMS.
flock (VMS, RISC OS, VOS) Not implemented.
fork (AmigaOS, RISC OS, VMS) Not implemented.
(Win32) Emulated using multiple interpreters. See perlfork.
(SunOS, Solaris, HP-UX) Does not automatically flush output
handles on some platforms.
getlogin
(RISC OS) Not implemented.
getpgrp (Win32, VMS, RISC OS) Not implemented.
getppid (Win32, RISC OS) Not implemented.
getpriority
(Win32, VMS, RISC OS, VOS) Not implemented.
getpwnam
(Win32) Not implemented.
(RISC OS) Not useful.
getgrnam
(Win32, VMS, RISC OS) Not implemented.
getnetbyname
(Android, Win32, Plan 9) Not implemented.
getpwuid
(Win32) Not implemented.
(RISC OS) Not useful.
getgrgid
(Win32, VMS, RISC OS) Not implemented.
getnetbyaddr
(Android, Win32, Plan 9) Not implemented.
getprotobynumber
(Android) Not implemented.
getpwent
(Android, Win32) Not implemented.
getgrent
(Android, Win32, VMS) Not implemented.
gethostbyname
(Irix 5) gethostbyname('localhost') does not work everywhere:
you may have to use gethostbyname('127.0.0.1').
gethostent
(Win32) Not implemented.
getnetent
(Android, Win32, Plan 9) Not implemented.
getprotoent
(Android, Win32, Plan 9) Not implemented.
getservent
(Win32, Plan 9) Not implemented.
seekdir (Android) Not implemented.
sethostent
(Android, Win32, Plan 9, RISC OS) Not implemented.
setnetent
(Win32, Plan 9, RISC OS) Not implemented.
setprotoent
(Android, Win32, Plan 9, RISC OS) Not implemented.
setservent
(Plan 9, Win32, RISC OS) Not implemented.
endpwent
(Win32) Not implemented.
(Android) Either not implemented or a no-op.
endgrent
(Android, RISC OS, VMS, Win32) Not implemented.
endhostent
(Android, Win32) Not implemented.
endnetent
(Android, Win32, Plan 9) Not implemented.
endprotoent
(Android, Win32, Plan 9) Not implemented.
endservent
(Plan 9, Win32) Not implemented.
getsockopt
(Plan 9) Not implemented.
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.
(VOS) Time values are 32-bit quantities.
ioctl (VMS) Not implemented.
(Win32) Available only for socket handles, and it does what the
ioctlsocket() call in the Winsock API does.
(RISC OS) Available only for socket handles.
kill (RISC OS) Not implemented, hence not useful for taint checking.
(Win32) "kill" 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.
(VMS) A pid of -1 indicating all processes on the system is not
currently supported.
link (RISC OS, VOS) Not implemented.
(AmigaOS) Link count not updated because hard links are not
quite that hard (They are sort of half-way between hard and soft
links).
(Win32) Hard links are implemented on Win32 under NTFS only.
They are natively supported on Windows 2000 and later. On
Windows NT they are implemented using the Windows POSIX
subsystem support and the Perl process will need Administrator
or Backup Operator privileges to create hard links.
(VMS) Available on 64 bit OpenVMS 8.2 and later.
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 (RISC OS) Not implemented.
(Win32) Treats directory junctions as symlinks.
msgctl
msgget
msgsnd
msgrcv (Android, Win32, VMS, Plan 9, RISC OS, VOS) Not implemented.
open (RISC OS) Open modes "|-" and "-|" are unsupported.
(SunOS, Solaris, HP-UX) Opening a process does not automatically
flush output handles on some platforms.
(Win32) Both of modes "|-" and "-|" are supported, but the list
form is emulated since the Win32 API CreateProcess() accepts a
simple string rather than an array of arguments. This may have
security implications for your code.
readlink
(VMS, RISC OS) Not implemented.
(Win32) readlink() on a directory junction returns the object
name, not a simple path.
rename (Win32) Can't move directories between directories on different
logical volumes.
rewinddir
(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.
select (Win32, VMS) Only implemented on sockets.
(RISC OS) Only reliable on sockets.
Note that the "select FILEHANDLE" form is generally portable.
semctl
semget
semop (Android, Win32, VMS, RISC OS) Not implemented.
setgrent
(Android, VMS, Win32, RISC OS) Not implemented.
setpgrp (Win32, VMS, RISC OS, VOS) Not implemented.
setpriority
(Win32, VMS, RISC OS, VOS) Not implemented.
setpwent
(Android, Win32, RISC OS) Not implemented.
setsockopt
(Plan 9) Not implemented.
shmctl
shmget
shmread
shmwrite
(Android, Win32, VMS, RISC OS) Not implemented.
sleep (Win32) Emulated using synchronization functions such that it
can be interrupted by "alarm", and limited to a maximum of
4294967 seconds, approximately 49 days.
socketpair
(RISC OS) Not implemented.
(VMS) Available on 64 bit OpenVMS 8.2 and later.
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.
(Mac OS X) "ctime" not supported on UFS.
(Win32) "ctime" is creation time instead of inode change time.
(VMS) "dev" and "ino" are not necessarily reliable.
(RISC OS) "mtime", "atime" and "ctime" all return the last
modification time. "dev" and "ino" are not necessarily
reliable.
(OS/2) "dev", "rdev", "blksize", and "blocks" are not available.
"ino" is not meaningful and will differ between stat calls on
the same file.
(Cygwin) Some versions of cygwin when doing a stat("foo") and
not finding it may then attempt to stat("foo.exe").
symlink (RISC OS) Not implemented.
(Win32) Requires either elevated permissions or developer mode
and a sufficiently recent version of Windows 10. You can check
whether the current process has the required privileges using
the Win32::IsSymlinkCreationAllowed() function.
Since Windows needs to know whether the target is a directory or
not when creating the link the target Perl will only create the
link as a directory link when the target exists and is a
directory.
Windows does not recognize forward slashes as path separators in
symbolic links. Hence on Windows, any "/" in the OLDFILE
parameter to symlink() are converted to "\". This is reflected
in the result returned by readlink(), the "\" in the result are
not converted back to "/".
(VMS) 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 (Win32, VMS, RISC OS, VOS) Not implemented.
sysopen (Mac OS, OS/390) 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.
system (Win32) As an optimization, may not call the command shell
specified in $ENV{PERL5SHELL}. "system(1, @args)" spawns an
external process and immediately returns its process designator,
without waiting for it to terminate. Return value may be used
subsequently in "wait" or "waitpid". Failure to spawn() a
subprocess is indicated by setting $? to "255 << 8". $? is set
in a way compatible with Unix (i.e. the exit status of the
subprocess is obtained by "$? >> 8", as described in the
documentation).
Note that the list form of system() is emulated since the Win32
API CreateProcess() accepts a simple string rather than an array
of command-line arguments. This may have security implications
for your code.
(RISC OS) There is no shell to process metacharacters, and the
native standard is to pass a command line terminated by "\n"
"\r" or "\0" to the spawned program. Redirection such as ">
foo" is 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, provided
the child program uses a compatible version of the emulation
library. "system SCALAR" will call the native command line
directly and no such emulation of a child Unix program will
occur. Mileage will vary.
(Win32) "system LIST" without the use of indirect object syntax
("system PROGRAM LIST") may fall back to trying the shell if the
first spawn() fails.
(SunOS, Solaris, HP-UX) Does not automatically flush output
handles on some platforms.
(VMS) As with Win32, "system(1, @args)" spawns an external
process and immediately returns its process designator without
waiting for the process to terminate. In this case the return
value may be used subsequently in "wait" or "waitpid".
Otherwise 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.
telldir (Android) Not implemented.
times (Win32) "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.
(RISC OS) Not useful.
truncate
(Older versions of VMS) Not implemented.
(VOS) Truncation to same-or-shorter lengths only.
(Win32) If a FILEHANDLE is supplied, it must be writable and
opened in append mode (i.e., use "open(my $fh, '>>',
'filename')" or "sysopen(my $fh, ..., O_APPEND|O_RDWR)". If a
filename is supplied, it should not be held open elsewhere.
umask Returns "undef" where unavailable.
(AmigaOS) "umask" works but the correct permissions are set only
when the file is finally closed.
utime (VMS, RISC OS) Only the modification time is updated.
(Win32) 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.
wait
waitpid (Win32) Can only be applied to process handles returned for
processes spawned using "system(1, ...)" or pseudo processes
created with "fork".
(RISC OS) Not useful.
Supported Platforms
The following platforms are known to build Perl 5.12 (as of April 2010,
its release date) from the standard source code distribution available
at <http://www.cpan.org/src>
Linux (x86, ARM, IA64)
HP-UX
AIX
Win32
Windows 2000
Windows XP
Windows Server 2003
Windows Vista
Windows Server 2008
Windows 7
Cygwin
Some tests are known to fail:
• ext/XS-APItest/t/call_checker.t - see
<https://github.com/Perl/perl5/issues/10750>
• dist/I18N-Collate/t/I18N-Collate.t
• ext/Win32CORE/t/win32core.t - may fail on recent cygwin
installs.
Solaris (x86, SPARC)
OpenVMS
Alpha (7.2 and later)
I64 (8.2 and later)
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
Stratus VOS / OpenVOS
AIX
Android
FreeMINT
Perl now builds with FreeMiNT/Atari. It fails a few tests, that
needs some investigation.
The FreeMiNT port uses GNU dld for loadable module capabilities. So
ensure you have that library installed when building perl.
EOL Platforms
(Perl 5.37.1)
The following platforms were supported by a previous version of Perl but
have been officially removed from Perl's source code as of 5.37.1:
Ultrix
(Perl 5.36)
The following platforms were supported by a previous version of Perl but
have been officially removed from Perl's source code as of 5.36:
NetWare
DOS/DJGPP
AT&T UWIN
(Perl 5.20)
The following platforms were supported by a previous version of Perl but
have been officially removed from Perl's source code as of 5.20:
AT&T 3b1
(Perl 5.14)
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
(Perl 5.12)
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
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
BSD/OS (BSDi)
Cygwin
DG/UX
DOS DJGPP 1)
DYNIX/ptx
EPOC R5
FreeBSD
HI-UXMPP (Hitachi) (5.8.0 worked but we didn't know it)
HP-UX
IRIX
Linux
Mac OS Classic
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)
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 3
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 champion on these
platforms--or both. They used to work, though, so go ahead and try
compiling them, and let <https://github.com/Perl/perl5/issues> know of
any trouble.
3b1
A/UX
ConvexOS
CX/UX
DC/OSx
DDE SMES
DOS EMX
Dynix
EP/IX
ESIX
FPS
GENIX
Greenhills
ISC
MachTen 68k
MPC
NEWS-OS
NextSTEP
OpenSTEP
Opus
Plan 9
RISC/os
SCO ODT/OSR
Stellar
SVR2
TI1500
TitanOS
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.
SEE ALSO
perlaix, perlamiga, perlbs2000, perlcygwin, perlebcdic, perlfreebsd,
perlhurd, perlhpux, perlirix, perlmacosx, perlos2, perlos390, perlos400,
perlplan9, perlqnx, perlsolaris, perltru64, perlunicode, perlvms,
perlvos, perlwin32, and Win32.
AUTHORS / CONTRIBUTORS
Abigail <abigail@abigail.be>, Charles Bailey <bailey@newman.upenn.edu>,
Graham Barr <gbarr@pobox.com>, Tom Christiansen <tchrist@perl.com>,
Nicholas Clark <nick@ccl4.org>, Thomas Dorner <Thomas.Dorner@start.de>,
Andy Dougherty <doughera@lafayette.edu>, Dominic Dunlop
<domo@computer.org>, Neale Ferguson <neale@vma.tabnsw.com.au>, David J.
Fiander <davidf@mks.com>, Paul Green <Paul.Green@stratus.com>, M.J.T.
Guy <mjtg@cam.ac.uk>, Jarkko Hietaniemi <jhi@iki.fi>, Luther Huffman
<lutherh@stratcom.com>, Nick Ing-Simmons <nick@ing-simmons.net>, Andreas
J. König <a.koenig@mind.de>, Markus Laker <mlaker@contax.co.uk>, Andrew
M. Langmead <aml@world.std.com>, Lukas Mai <l.mai@web.de>, Larry Moore
<ljmoore@freespace.net>, Paul Moore <Paul.Moore@uk.origin-it.com>, Chris
Nandor <pudge@pobox.com>, Matthias Neeracher <neeracher@mac.com>, Philip
Newton <pne@cpan.org>, Gary Ng <71564.1743@CompuServe.COM>, Tom Phoenix
<rootbeer@teleport.com>, André Pirard <A.Pirard@ulg.ac.be>, Peter
Prymmer <pvhp@forte.com>, Hugo van der Sanden <hv@crypt0.demon.co.uk>,
Gurusamy Sarathy <gsar@activestate.com>, Paul J. Schinder
<schinder@pobox.com>, Michael G Schwern <schwern@pobox.com>, Dan
Sugalski <dan@sidhe.org>, Nathan Torkington <gnat@frii.com>, John
Malmberg <wb8tyw@qsl.net>
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