perlport
(1)
Name
perlport - Writing portable Perl
Synopsis
Please see following description for synopsis
Description
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 have the full
generality of being portable, or whether to just get the job
done right now. This is the hardest choice to be made. The
rest is easy, because Perl provides many choices, whichever
way you want to approach your problem.
Looking at it another way, writing portable code is usually
about willfully limiting your available choices. Naturally,
it takes discipline and sacrifice to do that. The product
of portability and convenience may be a constant. You have
been warned.
Be aware of two important points:
Not all Perl programs have to be portable
There is no reason you should not use Perl as a language
to glue Unix tools together, or to prototype a Macintosh
application, or to manage the Windows registry. If it
makes no sense to aim for portability for one reason or
another in a given program, then don't bother.
Nearly all of Perl already is portable
Don't be fooled into thinking that it is hard to create
portable Perl code. It isn't. Perl tries its level-
best to bridge the gaps between what's available on
different platforms, and all the means available to use
those features. Thus almost all Perl code runs on any
machine without modification. But there are some
significant issues in writing portable code, and this
document is entirely about those issues.
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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", 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 $/ to the appropriate value
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for your file format before using chomp().
Because of the "text" mode translation, DOSish perls have
limitations in using "seek" and "tell" on a file accessed in
"text" mode. Stick to "seek"-ing to locations you got from
"tell" (and no others), and you are usually free to use
"seek" and "tell" even in "text" mode. Using "seek" or
"tell" or other file operations may be non-portable. If you
use "binmode" on a file, however, you can usually "seek" and
"tell" with arbitrary values in safety.
A common misconception in socket programming is that "\n" eq
"\012" everywhere. When using protocols such as common
Internet protocols, "\012" and "\015" are called for
specifically, and the values of the logical "\n" and "\r"
(carriage return) are not reliable.
print SOCKET "Hi there, client!\r\n"; # WRONG
print SOCKET "Hi there, client!\015\012"; # RIGHT
However, using "\015\012" (or "\cM\cJ", or "\x0D\x0A") can
be tedious and unsightly, as well as confusing to those
maintaining the code. As such, the Socket module supplies
the Right Thing for those who want it.
use Socket qw(:DEFAULT :crlf);
print SOCKET "Hi there, client!$CRLF" # RIGHT
When reading from a socket, remember that the default input
record separator $/ is "\n", but robust socket code will
recognize as either "\012" or "\015\012" as end of line:
while (<SOCKET>) {
# ...
}
Because both CRLF and LF end in LF, the input record
separator can be set to LF and any CR stripped later.
Better to write:
use Socket qw(:DEFAULT :crlf);
local($/) = 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).
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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
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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 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 5.9.2, 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 (included in the standard distribution as of
Perl 5.005) 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.
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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.
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
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whatever platform happens to be running the program.
use File::Spec::Functions;
chdir(updir()); # go up one directory
my $file = catfile(curdir(), 'temp', 'file.txt');
# on Unix and Win32, './temp/file.txt'
# on Mac OS Classic, ':temp:file.txt'
# on VMS, '[.temp]file.txt'
File::Spec is available in the standard distribution as of
version 5.004_05. File::Spec::Functions is only in
File::Spec 0.7 and later, and some versions of perl come
with version 0.6. If File::Spec is not updated to 0.7 or
later, you must use the object-oriented interface from
File::Spec (or upgrade File::Spec).
In general, production code should not have file paths
hardcoded. Making them user-supplied or read from a
configuration file is better, keeping in mind that file path
syntax varies on different machines.
This is especially noticeable in scripts like Makefiles and
test suites, which often assume "/" as a path separator for
subdirectories.
Also of use is File::Basename from the standard
distribution, which splits a pathname into pieces (base
filename, full path to directory, and file suffix).
Even when on a single platform (if you can call Unix a
single platform), remember not to count on the existence or
the contents of particular system-specific files or
directories, like /etc/passwd, /etc/sendmail.conf,
/etc/resolv.conf, or even /tmp/. For example, /etc/passwd
may exist but not contain the encrypted passwords, because
the system is using some form of enhanced security. Or it
may not contain all the accounts, because the system is
using NIS. If code does need to rely on such a file,
include a description of the file and its format in the
code's documentation, then make it easy for the user 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.
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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.)
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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 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
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generated. The specific names that are dynamically
generated may vary with the version of the C library on VMS,
and more may exist than is documented.
On VMS by default, changes to the %ENV hash are persistent
after the process exits. This can cause unintended issues.
Don't count on signals or %SIG for anything.
Don't count on filename globbing. Use "opendir", "readdir",
and "closedir" instead.
Don't count on per-program environment variables, or per-
program current directories.
Don't count on specific values of $!, neither numeric nor
especially the strings values. Users may switch their
locales causing error messages to be translated into their
languages. If you can trust a POSIXish environment, you can
portably use the symbols defined by the Errno module, like
ENOENT. And don't trust on the values of $! at all except
immediately after a failed system call.
Command names versus file pathnames
Don't assume that the name used to invoke a command or
program with "system" or "exec" can also be used to test for
the existence of the file that holds the executable code for
that command or program. 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, DJGPP, 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
"_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 $thisperl =~ m/$Config{_exe}$/i;}
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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.
Interprocess Communication (IPC)
In general, don't directly access the system in code meant
to be portable. That means, no "system", "exec", "fork",
"pipe", "``", "qx//", "open" with a "|", nor any of the
other things that makes being a perl hacker worth being.
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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(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
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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 NBDM_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 to 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.
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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.
If you really want to be international, you should consider
Unicode. See perluniintro and perlunicode for more
information.
If you want to use non-ASCII bytes (outside the bytes
0x00..0x7f) in the "source code" of your code, to be
portable you have to be explicit about what bytes they are.
Someone might for example be using your code under a UTF-8
locale, in which case random native bytes might be illegal
("Malformed UTF-8 ...") This means that for example
embedding ISO 8859-1 bytes beyond 0x7f into your strings
might cause trouble later. If the bytes are native 8-bit
bytes, you can use the "bytes" pragma. If the bytes are in
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a string (regular expression being a curious string), you
can often also use the "\xHH" notation instead of embedding
the bytes as-is. (If you want to write your code in UTF-8,
you can use the "utf8".) The "bytes" and "utf8" pragmata are
available since Perl 5.6.0.
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:
# NOTE: this is no longer "bad" in perl5.005
for (0..10000000) {} # bad
for (my $x = 0; $x <= 10000000; ++$x) {} # good
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).
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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 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:
o Mailing list: [email protected]
o Testing results: http://testers.cpan.org/
PLATFORMS
As of version 5.002, 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.
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%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
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.
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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 nothing about their data.
The $^O variable and the $Config{archname} values for
various DOSish perls are as follows:
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OS $^O $Config{archname} ID Version
--------------------------------------------------------
MS-DOS dos ?
PC-DOS dos ?
OS/2 os2 ?
Windows 3.1 ? ? 0 3 01
Windows 95 MSWin32 MSWin32-x86 1 4 00
Windows 98 MSWin32 MSWin32-x86 1 4 10
Windows ME MSWin32 MSWin32-x86 1 ?
Windows NT MSWin32 MSWin32-x86 2 4 xx
Windows NT MSWin32 MSWin32-ALPHA 2 4 xx
Windows NT MSWin32 MSWin32-ppc 2 4 xx
Windows 2000 MSWin32 MSWin32-x86 2 5 00
Windows XP MSWin32 MSWin32-x86 2 5 01
Windows 2003 MSWin32 MSWin32-x86 2 5 02
Windows Vista MSWin32 MSWin32-x86 2 6 00
Windows 7 MSWin32 MSWin32-x86 2 6 01
Windows 7 MSWin32 MSWin32-x64 2 6 01
Windows CE MSWin32 ? 3
Cygwin cygwin cygwin
The various MSWin32 Perl's can distinguish the OS they are
running on via the value of the fifth element of the list
returned from Win32::GetOSVersion(). For example:
if ($^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. [email protected],
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/
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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.
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
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 "$read = <STDIN>;".
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The VMS operating system has two filesystems, known as ODS-2
and ODS-5.
For ODS-2, filenames are in the format
"name.extension;version". The maximum length for filenames
is 39 characters, and the maximum length for extensions is
also 39 characters. Version is a number from 1 to 32767.
Valid characters are "/[A-Z0-9$_-]/".
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 specification they should return a VMS
format unless they are documented to do a conversion.
For routines that generate return a file specification, VMS
allows setting if the C library which Perl is built on if it
will be returned in VMS format or in Unix format.
With the ODS-2 file system, there is not much difference in
syntax of filenames without paths for VMS or Unix. With the
extended character set available with ODS-5 there can be a
significant difference.
Because of this, existing Perl scripts written for VMS were
sometimes 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
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a Unix system.
VMS file specifications without extensions have a trailing
dot. An equivalent Unix file specification should not show
the trailing dot.
The result of all of this, is that for VMS, for portable
scripts, you can not depend on Perl to present the filenames
in lowercase, to be case sensitive, and that the filenames
could be returned in either Unix or VMS format.
And if a routine returns a file specification, unless it is
intended to convert it, it should return it in the same
format as it found it.
"readdir" by default has traditionally returned lowercased
filenames. When the ODS-5 support is enabled, it will
return the exact case of the filename on the disk.
Files without extensions have a trailing period on them, so
doing a "readdir" in the default mode with a file named A.;5
will return a. when VMS is (though that file could be opened
with "open(FH, 'A')").
With support for extended file specifications and if
"opendir" was given a Unix format directory, a file named
A.;5 will return a and optionally in the exact case on the
disk. When "opendir" is given a VMS format directory, then
"readdir" should return a., and again with the optionally
the exact case.
RMS had an eight level limit on directory depths from any
rooted logical (allowing 16 levels overall) prior to VMS
7.2, and even with versions of VMS on VAX up through 7.3.
Hence "PERL_ROOT:[LIB.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
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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", "\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.
TCP/IP stacks are optional on VMS, so socket routines might
not be implemented. UDP sockets may not be supported.
The TCP/IP library support for all current versions of VMS
is dynamically loaded if present, so even if the routines
are configured, they may return a status indicating that
they are not implemented.
The value of $^O on OpenVMS is "VMS". 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 (grep(/VMS_AXP/, @INC)) {
print "I'm on Alpha!\n";
} elsif (grep(/VMS_VAX/, @INC)) {
print "I'm on VAX!\n";
} elsif (grep(/VMS_IA64/, @INC)) {
print "I'm on IA64!\n";
} else {
print "I'm not so sure about where $^O is...\n";
}
In general, the significant differences should only be if
Perl is running on VMS_VAX or one of the 64 bit OpenVMS
platforms.
On VMS, perl determines the UTC offset from the
"SYS$TIMEZONE_DIFFERENTIAL" logical name. Although the VMS
epoch began at 17-NOV-1858 00:00:00.00, calls to "localtime"
are adjusted to count offsets from 01-JAN-1970 00:00:00.00,
just like Unix.
Also see:
o README.vms (installed as README_vms), perlvms
o vmsperl list, [email protected]
o vmsperl on the web,
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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 matching "tr/
!#%&'()*;<=>?//".
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 any character
matching "tr/#%*<>?//". There are restrictions involving
spaces and apostrophies: 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 $^O on VOS is "VOS". To determine the
architecture that you are running on without resorting to
loading all of %Config you can examine the content of the
@INC array like so:
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if ($^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 post comments to the comp.sys.stratus newsgroup, or
use the contact information located in the distribution
files on the Stratus Anonymous FTP site.
o VOS Perl on the web at
http://ftp.stratus.com/pub/vos/posix/posix.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 5.8.1/5.9.0 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.
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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
OS/390 & VM/ESA):
print "Content-type: text/html\r\n\r\n";
The values of $^O on some of these platforms includes:
uname $^O $Config{'archname'}
--------------------------------------------
OS/390 os390 os390
OS400 os400 os400
POSIX-BC posix-bc BS2000-posix-bc
VM/ESA vmesa vmesa
Some simple tricks for determining if you are running on an
EBCDIC platform could include any of the following (perhaps
all):
if ("\t" eq "\05") { print "EBCDIC may be spoken here!\n"; }
if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; }
if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; }
One thing you may not want to rely on is the EBCDIC encoding
of punctuation characters since these may differ from code
page to code page (and once your module or script is
rumoured to work with EBCDIC, folks will want it to work
with all EBCDIC character sets).
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Also see:
o perlos390, README.os390, perlbs2000, README.vmesa,
perlebcdic.
o The [email protected] list is for discussion of porting
issues as well as general usage issues for all EBCDIC
Perls. Send a message body of "subscribe perl-mvs" to
[email protected].
o AS/400 Perl information at
http://as400.rochester.ibm.com/ as well as on CPAN in
the ports/ directory.
Acorn RISC OS
Because Acorns use ASCII with newlines ("\n") in text files
as "\012" like Unix, and because Unix filename emulation is
turned on by default, most simple scripts will probably work
"out of the box". The native filesystem is modular, and
individual filesystems are free to be case-sensitive or
insensitive, and are usually case-preserving. Some native
filesystems have name length limits, which file and
directory names are silently truncated to fit. Scripts
should be aware that the standard filesystem currently has a
name length limit of 10 characters, with up to 77 items in a
directory, but other filesystems may not impose such
limitations.
Native filenames are of the form
Filesystem#Special_Field::DiskName.$.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|/.|./|;"
Note that ""ADFS::HardDisk.$.File" ne
'ADFS::HardDisk.$.File'" and that the second stage of "$"
interpolation in regular expressions will fall foul of the
$. if scripts are not careful.
Logical paths specified by system variables containing
comma-separated search lists are also allowed; hence
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"System:Modules" is a valid filename, and the filesystem
will prefix "Modules" with each section of "System$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$Name". Each
filesystem maintains a current directory, and the current
filesystem's current directory is the global current
directory. Consequently, sociable programs don't change the
current directory but rely on full pathnames, and programs
(and Makefiles) cannot assume that they can spawn a child
process which can change the current directory without
affecting its parent (and everyone else for that matter).
Because native operating system filehandles are global and
are currently allocated down from 255, with 0 being a
reserved value, the Unix emulation library emulates Unix
filehandles. Consequently, you can't rely on passing
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"STDIN", "STDOUT", or "STDERR" to your children.
The desire of users to express filenames of the form
"<Foo$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,
BeOS, HP MPE/iX, 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
BeOS beos
MPE/iX mpeix PA-RISC1.1
See also:
o Amiga, README.amiga (installed as perlamiga).
o Be OS, README.beos
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o HP 300 MPE/iX, README.mpeix and Mark Bixby's web page
http://www.bixby.org/mark/porting.html
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.
o Plan 9, README.plan9
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 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 "-w" only inspects the read-only file attribute
(FILE_ATTRIBUTE_READONLY), which determines whether
the directory can be deleted, not whether it can be
written to. Directories always have read and write
access unless denied by discretionary access control
lists (DACLs). (Win32)
"-r", "-w", "-x", and "-o" tell whether the file is
accessible, which may not reflect UIC-based file
protections. (VMS)
"-s" by name on an open file will return the space
reserved on disk, rather than the current extent.
"-s" on an open filehandle returns the current size.
(RISC OS)
"-R", "-W", "-X", "-O" are indistinguishable from
"-r", "-w", "-x", "-o". (Win32, VMS, RISC OS)
"-g", "-k", "-l", "-u", "-A" are not particularly
meaningful. (Win32, VMS, RISC OS)
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"-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)
chmod Only good for changing "owner" read-write access,
"group", and "other" bits are meaningless. (Win32)
Only good for changing "owner" and "other" read-
write access. (RISC OS)
Access permissions are mapped onto VOS access-
control list changes. (VOS)
The actual permissions set depend on the value of
the "CYGWIN" in the SYSTEM environment settings.
(Cygwin)
chown Not implemented. (Win32, Plan 9, RISC OS)
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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,
VM/ESA)
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 Implemented via Spawn. (VM/ESA)
Does not automatically flush output handles on some
platforms. (SunOS, Solaris, HP-UX)
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)
fcntl Not implemented. (Win32) Some functions available
based on the version of VMS. (VMS)
flock Not implemented (VMS, RISC OS, VOS).
Available only on Windows NT (not on Windows 95).
(Win32)
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fork Not implemented. (AmigaOS, RISC OS, VM/ESA, VMS)
Emulated using multiple interpreters. See perlfork.
(Win32)
Does not automatically flush output handles on some
platforms. (SunOS, Solaris, HP-UX)
getlogin
Not implemented. (RISC OS)
getpgrp Not implemented. (Win32, VMS, RISC OS)
getppid Not implemented. (Win32, RISC OS)
getpriority
Not implemented. (Win32, VMS, RISC OS, VOS, VM/ESA)
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, VM/ESA)
getgrent
Not implemented. (Win32, VMS, VM/ESA)
gethostbyname
"gethostbyname('localhost')" does not work
everywhere: you may have to use
"gethostbyname('127.0.0.1')". (Irix 5)
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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, Plan 9, RISC OS)
setnetent
Not implemented. (Win32, Plan 9, RISC OS)
setprotoent
Not implemented. (Win32, Plan 9, RISC OS)
setservent
Not implemented. (Plan 9, Win32, RISC OS)
endpwent
Not implemented. (MPE/iX, VM/ESA, Win32)
endgrent
Not implemented. (MPE/iX, RISC OS, VM/ESA, 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
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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)
Is not supported for process identification number
of 0 or negative numbers. (VMS)
link Not implemented. (MPE/iX, RISC OS, VOS)
Link count not updated because hard links are not
quite that hard (They are sort of half-way between
hard and soft links). (AmigaOS)
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.
Available on 64 bit OpenVMS 8.2 and later. (VMS)
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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)
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. (MPE/iX, VMS, Win32, RISC OS)
setpgrp Not implemented. (Win32, VMS, RISC OS, VOS)
setpriority
Not implemented. (Win32, VMS, RISC OS, VOS)
setpwent
Not implemented. (MPE/iX, Win32, RISC OS)
setsockopt
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Not implemented. (Plan 9)
shmctl
shmget
shmread
shmwrite
Not implemented. (Win32, VMS, RISC OS, VOS)
sockatmark
A relatively recent addition to socket functions,
may not be implemented even in Unix platforms.
socketpair
Not implemented. (RISC OS, VM/ESA)
Available on OpenVOS Release 17.0 or later. (VOS)
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)
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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, VM/ESA)
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, VM/ESA)
system 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".
$? is set in a way compatible with Unix (i.e. the
exitstatus of the subprocess is obtained by "$? >>
8", as described in the documentation). (Win32)
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, 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
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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 Returns undef where unavailable, as of version
5.005.
"umask" works but the correct permissions are set
only when the file is finally closed. (AmigaOS)
utime Only the modification time is updated. (BeOS, 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)
Not useful. (RISC OS)
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
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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
Haiku
Irix (6.5. What else?)
OpenBSD
Dragonfly BSD
MirOS BSD
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 5.12)
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
The following platforms may still work as of Perl 5.12, but
Perl's developers have made an explicit decision to
discontinue support for them:
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/
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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)
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
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.
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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 champion on these
platforms--or both. They used to work, though, so go ahead
and try compiling them, and let [email protected] 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
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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.
ATTRIBUTES
See attributes(5) for descriptions of the following
attributes:
+---------------+------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+------------------+
|Availability | runtime/perl-512 |
+---------------+------------------+
|Stability | Uncommitted |
+---------------+------------------+
SEE ALSO
perlaix, perlamiga, perlapollo, perlbeos, perlbs2000,
perlce, perlcygwin, perldgux, perldos, perlepoc, perlebcdic,
perlfreebsd, perlhurd, perlhpux, perlirix, perlmacos,
perlmacosx, perlmpeix, perlnetware, perlos2, perlos390,
perlos400, perlplan9, perlqnx, perlsolaris, perltru64,
perlunicode, perlvmesa, perlvms, perlvos, perlwin32, and
Win32.
AUTHORS / CONTRIBUTORS
Abigail <[email protected]>, Charles Bailey
<[email protected]>, Graham Barr <[email protected]>,
Tom Christiansen <[email protected]>, Nicholas Clark
perl v5.12.5 Last change: 2012-11-03 43
Perl Programmers Reference Guide PERLPORT(1)
<[email protected]>, Thomas Dorner <[email protected]>,
Andy Dougherty <[email protected]>, Dominic Dunlop
<[email protected]>, Neale Ferguson
<[email protected]>, David J. Fiander
<[email protected]>, Paul Green <[email protected]>,
M.J.T. Guy <[email protected]>, Jarkko Hietaniemi <[email protected]>,
Luther Huffman <[email protected]>, Nick Ing-Simmons
<[email protected]>, Andreas J. Koenig
<[email protected]>, Markus Laker <[email protected]>,
Andrew M. Langmead <[email protected]>, Larry Moore
<[email protected]>, Paul Moore
<[email protected]>, Chris Nandor
<[email protected]>, Matthias Neeracher <[email protected]>,
Philip Newton <[email protected]>, Gary Ng
<[email protected]>, Tom Phoenix
<[email protected]>, Andre Pirard <[email protected]>,
Peter Prymmer <[email protected]>, Hugo van der Sanden
<[email protected]>, Gurusamy Sarathy
<[email protected]>, Paul J. Schinder
<[email protected]>, Michael G Schwern <[email protected]>,
Dan Sugalski <[email protected]>, Nathan Torkington
<[email protected]>. John Malmberg <[email protected]>
NOTES
This software was built from source available at
https://java.net/projects/solaris-userland. The original
community source was downloaded from
http://www.cpan.org/src/5.0/perl-5.12.5.tar.bz2
Further information about this software can be found on the
open source community website at http://www.perl.org/.
perl v5.12.5 Last change: 2012-11-03 44