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 impor-tant important
tant 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 pro-totype prototype
totype 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, Mac OS, 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 dif-ferences differences
ferences 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 vari-ous various
ous 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, STDIO 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 com-monly commonly
monly referred to as CRLF.
A common cause of unportable programs is the misuse of chop() to trim newlines:
# XXX UNPORTABLE!
while(<FILE>) {
chop;
@array = split(/:/);
#...
}
You can get away with this on Unix and Mac OS (they have a single character end-of-line), but the
same program will break under DOSish perls because you're only chop()ing half the end-of-line.
Instead, chomp() should be used to trim newlines. The Dunce::Files module can help audit your code
for misuses of chop().
When dealing with binary files (or text files in binary mode) be sure to explicitly set $/ to the
appropriate value for your file format before using chomp().
Because of the "text" mode translation, DOSish perls have limitations in using "seek" and "tell" on a
file accessed in "text" mode. Stick to "seek"-ing to locations you got from "tell" (and no others),
and you are usually free to use "seek" and "tell" even in "text" mode. Using "seek" or "tell" or
other file operations may be non-portable. If you use "binmode" on a file, however, you can usually
"seek" and "tell" with arbitrary values in safety.
A common misconception in socket programming is that "\n" eq "\012" everywhere. When using protocols
such as common Internet protocols, "\012" and "\015" are called for specifically, and the values of
the logical "\n" and "\r" (carriage return) are not reliable.
print SOCKET "Hi there, client!\r\n"; # WRONG
print SOCKET "Hi there, client!\015\012"; # RIGHT
However, using "\015\012" (or "\cM\cJ", or "\x0D\x0A") can be tedious and unsightly, as well as con-fusing confusing
fusing to those maintaining the code. As such, the Socket module supplies the Right Thing for those
who want it.
use Socket qw(:DEFAULT :crlf);
print SOCKET "Hi there, client!$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).
Similarly, functions that return text data--such as a function that fetches a web page--should some-times sometimes
times 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 --------------------------\n
\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 ---------------------\n
\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 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 guaran-teed guaranteed
teed to be portable.
As of perl 5.8.5, 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 pre-
cisely UTF-EBCDIC will go.
Files and Filesystems
Most platforms these days structure files in a hierarchical fashion. So, it is reasonably safe to
assume that all platforms support the notion of a "path" to uniquely identify a file on the system.
How that path is really written, though, differs considerably.
Although similar, file path specifications differ between Unix, Windows, Mac OS, OS/2, VMS, VOS,
RISC OS, and probably others. Unix, for example, is one of the few OSes that has the elegant idea of
a single root directory.
DOS, OS/2, VMS, VOS, and Windows can work similarly to Unix with "/" as path separator, or in their
own idiosyncratic ways (such as having several root directories and various "unrooted" device files
such NIL: and LPT:).
Mac OS uses ":" 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 inter-faces interfaces
faces like chmod() work, but sometimes there simply is no good mapping.
If all this is intimidating, have no (well, maybe only a little) fear. There are modules that can
help. The File::Spec modules provide methods to do the Right Thing on whatever platform happens to
be running the program.
use File::Spec::Functions;
chdir(updir()); # go up one directory
$file = catfile(curdir(), 'temp', 'file.txt');
# on Unix and Win32, './temp/file.txt'
# on Mac OS, ':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 con-tain contain
tain 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 max-imum maximum
imum 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-insensi-tive case-insensitive
tive 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) 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(FILE, '<', $existing_file) or die $!;
If filenames might use strange characters, it is safest to open it with "sysopen" instead of "open".
"open" is magic and can translate characters like ">", "<", and "|", which may be the wrong thing to
do. (Sometimes, though, it's the right thing.) Three-arg open can also help protect against this
translation in cases where it is undesirable.
Don't use ":" as a part of a filename since many systems use that for their own semantics (Mac OS
Classic for separating pathname components, many networking schemes and utilities for separating the
nodename and the pathname, and so on). For the same reasons, avoid "@", ";" and "|".
Don't assume that in pathnames you can collapse two leading slashes "//" into one: some networking
and clustering filesystems have special semantics for that. Let the operating system to sort it out.
The portable filename characters as defined by ANSI C are
a b c d e f g h i j k l m n o p q r t u v w x y z
A B C D E F G H I J K L M N O P Q R T U V W X Y Z
0 1 2 3 4 5 6 7 8 9
. _ -
and the "-" shouldn't be the first character. If you want to be hypercorrect, stay case-insensitive
and within the 8.3 naming convention (all the files and directories have to be unique within one
directory if their names are lowercased and truncated to eight characters before the ".", if any, and
to three characters after the ".", if any). (And do not use "."s in directory names.)
System Interaction
Not all platforms provide a command line. These are usually platforms that rely primarily on a
Graphical User Interface (GUI) for user interaction. A program requiring a command line interface
might not work everywhere. This is probably for the user of the program to deal 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 manda-tory mandatory
tory 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.
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 pro-gram. program.
gram. 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 gener-ally generally
ally 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;
$thisperl = $^X;
if ($^O ne 'VMS')
{$thisperl .= $Config{_exe} unless $thisperl =~ m/$Config{_exe}$/i;}
To convert $Config{perlpath} to a file pathname, say:
use Config;
$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 host-name hostname
name or a non-qualified hostname: it all depends on how the system had been configured. Also remem-ber remember
ber things like 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 pro-fessional. professional.
fessional.
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.
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 porta-ble portable
ble 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 inter-nally internally
nally implement it with platform-specific code, but expose a common interface).
External Subroutines (XS)
XS code can usually be made to work with any platform, but dependent libraries, header files, etc.,
might not be readily available or portable, or the XS code itself might be platform-specific, just as
Perl code might be. If the libraries and headers are portable, then it is normally reasonable to
make sure the XS code is portable, too.
A different type of portability issue arises when writing XS code: availability of a C compiler on
the end-user's system. C brings with it its own portability issues, and writing XS code will expose
you to some of those. Writing purely in Perl is an easier way to achieve portability.
Standard Modules
In general, the standard modules work across platforms. Notable exceptions are the CPAN module
(which currently makes connections to external programs that may not be available), platform-specific
modules (like ExtUtils::MM_VMS), and DBM modules.
There is no one DBM module available on all platforms. SDBM_File and the others are generally avail-able available
able on all Unix and DOSish ports, but not in MacPerl, where only NBDM_File and DB_File are avail-able. available.
able.
The good news is that at least some DBM module should be available, and AnyDBM_File will use which-ever whichever
ever module it can find. Of course, then the code needs to be fairly strict, dropping to the great-est greatest
est 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 Stan-dard Standard
dard 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 implementa-tion-specific. implementation-specific.
tion-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.
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;
$offset = Time::Local::timegm(0, 0, 0, 1, 0, 70);
The value for $offset in Unix will be 0, but in Mac OS 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.
On Windows (at least), you shouldn't pass a negative value to "gmtime" or "localtime".
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 perluni-code perlunicode
code 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 a string (regular expression being a curious string), you can often also use the "\xHH"
notation instead of embedding the bytes as-is. If they are in some particular legacy encoding (ether
single-byte or something more complicated), you can use the "encoding" pragma. (If you want to write
your code in UTF-8, you can use either the "utf8" pragma, or the "encoding" pragma.) The "bytes" and
"utf8" pragmata are available since Perl 5.6.0, and the "encoding" pragma since Perl 5.8.0.
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
@lines = <VERY_LARGE_FILE>; # bad
while (<FILE>) {$file .= $_} # sometimes bad
$file = join('', <FILE>); # 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, do not-- unfortunately. Thus the notion of user id, or "home" directory, or
even the state of being logged-in, may be unrecognizable on many platforms. If you write programs
that are security-conscious, it is usually best to know what type of system you will be running under
so that you can write code explicitly for that platform (or class of platforms).
Don't assume the UNIX filesystem access semantics: the operating system or the filesystem may be
using some ACL systems, which are richer languages than the usual rwx. Even if the rwx exist, their
semantics might be different.
(From security viewpoint testing for permissions before attempting to do something is silly anyway:
if one tries this, there is potential for race conditions-- someone or something might change the
permissions between the permissions check and the actual operation. Just try the operation.)
Don't assume the UNIX user and group semantics: especially, don't expect the $< and $> (or the $( and
$)) to work for switching identities (or memberships).
Don't assume set-uid and set-gid semantics. (And even if you do, think twice: set-uid and set-gid are
a known can of security worms.)
Style
For those times when it is necessary to have platform-specific code, consider keeping the platform-specific platformspecific
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 plat-forms platforms
forms 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@perl.org
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.
%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
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
MachTen PPC machten powerpc-machten
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:
$filespec0 = "c:/foo/bar/file.txt";
$filespec1 = "c:\\foo\\bar\\file.txt";
$filespec2 = 'c:\foo\bar\file.txt';
$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 con-
sistent 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 "New-
lines"). "binmode(FILEHANDLE)" will keep "\n" translated as "\012" for that filehandle. Since it is
a no-op on other systems, "binmode" should be used for cross-platform code that deals with binary
data. That's assuming you realize in advance that your data is in binary. General-purpose programs
should often assume nothing about their data.
The $^O variable and the $Config{archname} values for various DOSish perls are as follows:
OS $^O $Config{archname} ID Version
--------------------------------------------------------
MS-DOS dos ?
PC-DOS dos ?
OS/2 os2 ?
Windows 3.1 ? ? 0 3 01
Windows 95 MSWin32 MSWin32-x86 1 4 00
Windows 98 MSWin32 MSWin32-x86 1 4 10
Windows ME MSWin32 MSWin32-x86 1 ?
Windows NT MSWin32 MSWin32-x86 2 4 xx
Windows NT MSWin32 MSWin32-ALPHA 2 4 xx
Windows NT MSWin32 MSWin32-ppc 2 4 xx
Windows 2000 MSWin32 MSWin32-x86 2 5 00
Windows XP MSWin32 MSWin32-x86 2 5 01
Windows 2003 MSWin32 MSWin32-x86 2 5 02
Windows CE MSWin32 ? 3
Cygwin cygwin cygwin
The various MSWin32 Perl's can distinguish the OS they are running on via the value of the fifth ele-
ment of the list returned from Win32::GetOSVersion(). For example:
if ($^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:
The djgpp environment for DOS, http://www.delorie.com/djgpp/ and perldos.
The EMX environment for DOS, OS/2, etc. emx@iaehv.nl,
http://www.leo.org/pub/comp/os/os2/leo/gnu/emx+gcc/index.html or
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, http://www.activestate.com/
The Cygwin environment for Win32; README.cygwin (installed as perlcygwin), http://www.cygwin.com/
The U/WIN environment for Win32, http://www.research.att.com/sw/tools/uwin/
Build instructions for OS/2, perlos2
Mac OS
Any module requiring XS compilation is right out for most people, because MacPerl is built using non-
free (and non-cheap!) compilers. Some XS modules that can work with MacPerl are built and distrib-
uted in binary form on CPAN.
Directories are specified as:
volume:folder:file for absolute pathnames
volume:folder: for absolute pathnames
:folder:file for relative pathnames
:folder: for relative pathnames
:file for relative pathnames
file for relative pathnames
Files are stored in the directory in alphabetical order. Filenames are limited to 31 characters, and
may include any character except for null and ":", which is reserved as the path separator.
Instead of "flock", see "FSpSetFLock" and "FSpRstFLock" in the Mac::Files module, or "chmod(0444,
...)" and "chmod(0666, ...)".
In the MacPerl application, you can't run a program from the command line; programs that expect @ARGV
to be populated can be edited with something like the following, which brings up a dialog box asking
for the command line arguments.
if (!@ARGV) {
@ARGV = split /\s+/, MacPerl::Ask('Arguments?');
}
A MacPerl script saved as a "droplet" will populate @ARGV with the full pathnames of the files
dropped onto the script.
Mac users can run programs under a type of command line interface under MPW (Macintosh Programmer's
Workshop, a free development environment from Apple). MacPerl was first introduced as an MPW tool,
and MPW can be used like a shell:
perl myscript.plx some arguments
ToolServer is another app from Apple that provides access to MPW tools from MPW and the MacPerl app,
which allows MacPerl programs to use "system", backticks, and piped "open".
"Mac OS" is the proper name for the operating system, but the value in $^O is "MacOS". To determine
architecture, version, or whether the application or MPW tool version is running, check:
$is_app = $MacPerl::Version =~ /App/;
$is_tool = $MacPerl::Version =~ /MPW/;
($version) = $MacPerl::Version =~ /^(\S+)/;
$is_ppc = $MacPerl::Architecture eq 'MacPPC';
$is_68k = $MacPerl::Architecture eq 'Mac68K';
Mac OS X, based on NeXT's OpenStep OS, runs MacPerl natively, under the "Classic" environment. There
is no "Carbon" version of MacPerl to run under the primary Mac OS X environment. Mac OS X and its
Open Source version, Darwin, both run Unix perl natively.
Also see:
MacPerl Development, http://dev.macperl.org/ .
The MacPerl Pages, http://www.macperl.com/ .
The MacPerl mailing lists, http://lists.perl.org/ .
MPW, ftp://ftp.apple.com/developer/Tool_Chest/Core_Mac_OS_Tools/
VMS
Perl on VMS is discussed in perlvms in the perl distribution. 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 "$read = <STDIN>;".
Filenames are in the format "name.extension;version". The maximum length for filenames is 39 charac-
ters, and the maximum length for extensions is also 39 characters. Version is a number from 1 to
32767. Valid characters are "/[A-Z0-9$_-]/".
VMS's RMS filesystem is case-insensitive and does not preserve case. "readdir" returns lowercased
filenames, but specifying a file for opening remains case-insensitive. Files without extensions have
a trailing period on them, so doing a "readdir" with a file named A.;5 will return a. (though that
file could be opened with "open(FH, 'A')").
RMS had an eight level limit on directory depths from any rooted logical (allowing 16 levels overall)
prior to VMS 7.2. 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/".
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.
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 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";
} else {
print "I'm not so sure about where $^O is...\n";
}
On VMS, perl determines the UTC offset from the "SYS$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, majordomo@perl.org
(Put the words "subscribe vmsperl" in message body.)
vmsperl on the web, http://www.sidhe.org/vmsperl/index.html
VOS
Perl on VOS 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:
C<< $ perl -ne "print if /perl_setup/i" >system>notices >>
C<< $ perl -ne "print if /perl_setup/i" /system/notices >>
or even a mixture of both as in:
C<< $ 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 con-
tain a slash character cannot be processed. Such files must be renamed before they can be processed
by Perl. Note that VOS limits file names to 32 or fewer characters.
Perl on VOS can be built using two different compilers and two different versions of the POSIX run-
time. The recommended method for building full Perl is with the GNU C compiler and the generally-
available version of VOS POSIX support. See README.vos (installed as perlvos) for restrictions that
apply when Perl is built using the VOS Standard C compiler or the alpha version of VOS POSIX support.
The value of $^O on VOS is "VOS". To determine the architecture that you are running on without
resorting to loading all of %Config you can examine the content of the @INC array like so:
if ($^O =~ /VOS/) {
print "I'm on a Stratus box!\n";
} else {
print "I'm not on a Stratus box!\n";
die;
}
if (grep(/860/, @INC)) {
print "This box is a Stratus XA/R!\n";
} elsif (grep(/7100/, @INC)) {
print "This box is a Stratus HP 7100 or 8xxx!\n";
} elsif (grep(/8000/, @INC)) {
print "This box is a Stratus HP 8xxx!\n";
} else {
print "This box is a Stratus 68K!\n";
}
Also see:
README.vos (installed as perlvos)
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 subscribe to the general Stratus mailing list. Send a letter with "subscribe
Info-Stratus" in the message body to majordomo@list.stratagy.com.
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 inter-
nally (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 back-
ticks 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 pro-
cedure 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 $Config{'archname'}
--------------------------------------------
OS/390 os390 os390
OS400 os400 os400
POSIX-BC posix-bc BS2000-posix-bc
VM/ESA vmesa vmesa
Some simple tricks for determining if you are running on an EBCDIC platform could include any of the
following (perhaps all):
if ("\t" eq "\05") { print "EBCDIC may be spoken here!\n"; }
if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; }
if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; }
One thing you may not want to rely on is the EBCDIC encoding of punctuation characters since these
may differ from code page to code page (and once your module or script is rumoured to work with
EBCDIC, folks will want it to work with all EBCDIC character sets).
Also see:
perlos390, README.os390, perlbs2000, README.vmesa, perlebcdic.
The perl-mvs@perl.org list is for discussion of porting issues as well as general usage issues
for all EBCDIC Perls. Send a message body of "subscribe perl-mvs" to majordomo@perl.org.
AS/400 Perl information at http://as400.rochester.ibm.com/ as well as on CPAN in the ports/
directory.
Acorn RISC OS
Because Acorns use ASCII with newlines ("\n") in text files as "\012" like Unix, and because Unix
filename emulation is turned on by default, most simple scripts will probably work "out of the box".
The native filesystem is modular, and individual filesystems are free to be case-sensitive or insen-
sitive, and are usually case-preserving. Some native filesystems have name length limits, which file
and directory names are silently truncated to fit. Scripts should be aware that the standard
filesystem currently has a name length limit of 10 characters, with up to 77 items in a directory,
but other filesystems may not impose such limitations.
Native filenames are of the form
Filesystem#Special_Field::DiskName.$.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 $. if scripts are not careful.
Logical paths specified by system variables containing comma-separated search lists are also allowed;
hence "System:Modules" is a valid filename, and the filesystem will prefix "Modules" with each sec-
tion of "System$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>.Mod-
ules" 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 fash-
ion. 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$Name". Each filesystem maintains a current
directory, and the current filesystem's current directory is the global current directory. Conse-
quently, sociable programs don't change the current directory but rely on full pathnames, and pro-
grams (and Makefiles) cannot assume that they can spawn a child process which can change the current
directory without affecting its parent (and everyone else for that matter).
Because native operating system filehandles are global and are currently allocated down from 255,
with 0 being a reserved value, the Unix emulation library emulates Unix filehandles. Consequently,
you can't rely on passing "STDIN", "STDOUT", or "STDERR" to your children.
The desire of users to express filenames of the form "<Foo$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, Atari MiNT, 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 infor-
mation, and possibly binaries, for the likes of: aos, Atari ST, lynxos, riscos, Novell Netware, Tan-
dem 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:
Amiga, README.amiga (installed as perlamiga).
Atari, README.mint and Guido Flohr's web page http://stud.uni-sb.de/~gufl0000/
Be OS, README.beos
HP 300 MPE/iX, README.mpeix and Mark Bixby's web page http://www.bixby.org/mark/perlix.html
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.
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 accompa-
nying 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 "-r", "-w", and "-x" have a limited meaning only; directories and applications are exe-
cutable, and there are no uid/gid considerations. "-o" is not supported. (Mac OS)
"-r", "-w", "-x", and "-o" tell whether the file is accessible, which may not reflect UIC-
based file protections. (VMS)
"-s" returns the size of the data fork, not the total size of data fork plus resource fork.
(Mac 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. (RISC OS)
"-R", "-W", "-X", "-O" are indistinguishable from "-r", "-w", "-x", "-o". (Mac OS, Win32,
VMS, RISC OS)
"-b", "-c", "-k", "-g", "-p", "-u", "-A" are not implemented. (Mac OS)
"-g", "-k", "-l", "-p", "-u", "-A" are not particularly meaningful. (Win32, VMS, RISC OS)
"-d" is true if passed a device spec without an explicit directory. (VMS)
"-T" and "-B" are implemented, but might misclassify Mac text files with foreign characters;
this is the case will all platforms, but may affect Mac OS often. (Mac OS)
"-x" (or "-X") determine if a file ends in one of the executable suffixes. "-S" is meaning-
less. (Win32)
"-x" (or "-X") determine if a file has an executable file type. (RISC OS)
atan2 Y,X
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.open-
group.org/onlinepubs/009695399/functions/atan2.html.
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.open-
group.org/onlinepubs/009695399/functions/atan2.html.
binmode Meaningless. (Mac OS, 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 limited meaning. Disabling/enabling write permission is mapped to locking/unlocking the
file. (Mac OS)
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 set-tings. settings.
tings. (Cygwin)
chown Not implemented. (Mac OS, Win32, Plan 9, RISC OS, VOS)
Does nothing, but won't fail. (Win32)
chroot Not implemented. (Mac OS, 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)
Not implemented. (VOS)
dbmclose
Not implemented. (VMS, Plan 9, VOS)
dbmopen Not implemented. (VMS, Plan 9, VOS)
dump Not useful. (Mac OS, RISC OS)
Not implemented. (Win32)
Invokes VMS debugger. (VMS)
exec Not implemented. (Mac OS)
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. (VMS)
fcntl Not implemented. (Win32, VMS)
flock Not implemented (Mac OS, VMS, RISC OS, VOS).
Available only on Windows NT (not on Windows 95). (Win32)
fork Not implemented. (Mac OS, AmigaOS, RISC OS, VOS, 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. (Mac OS, RISC OS)
getpgrp Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)
getppid Not implemented. (Mac OS, Win32, RISC OS)
getpriority
Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS, VM/ESA)
getpwnam
Not implemented. (Mac OS, Win32)
Not useful. (RISC OS)
getgrnam
Not implemented. (Mac OS, Win32, VMS, RISC OS)
getnetbyname
Not implemented. (Mac OS, Win32, Plan 9)
getpwuid
Not implemented. (Mac OS, Win32)
Not useful. (RISC OS)
getgrgid
Not implemented. (Mac OS, Win32, VMS, RISC OS)
getnetbyaddr
Not implemented. (Mac OS, Win32, Plan 9)
getprotobynumber
Not implemented. (Mac OS)
getservbyport
Not implemented. (Mac OS)
getpwent
Not implemented. (Mac OS, Win32, VM/ESA)
getgrent
Not implemented. (Mac OS, Win32, VMS, VM/ESA)
gethostbyname
"gethostbyname('localhost')" does not work everywhere: you may have to use "gethostby-name('127.0.0.1')". "gethostbyname('127.0.0.1')".
name('127.0.0.1')". (Mac OS, Irix 5)
gethostent
Not implemented. (Mac OS, Win32)
getnetent
Not implemented. (Mac OS, Win32, Plan 9)
getprotoent
Not implemented. (Mac OS, Win32, Plan 9)
getservent
Not implemented. (Win32, Plan 9)
sethostent
Not implemented. (Mac OS, Win32, Plan 9, RISC OS)
setnetent
Not implemented. (Mac OS, Win32, Plan 9, RISC OS)
setprotoent
Not implemented. (Mac OS, Win32, Plan 9, RISC OS)
setservent
Not implemented. (Plan 9, Win32, RISC OS)
endpwent
Not implemented. (Mac OS, MPE/iX, VM/ESA, Win32)
endgrent
Not implemented. (Mac OS, MPE/iX, RISC OS, VM/ESA, VMS, Win32)
endhostent
Not implemented. (Mac OS, Win32)
endnetent
Not implemented. (Mac OS, Win32, Plan 9)
endprotoent
Not implemented. (Mac OS, 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 Same portability caveats as localtime.
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 "kill(0, LIST)" is implemented for the sake of taint checking; use with other signals is
unimplemented. (Mac OS)
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 iden-tified identified
tified 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)
link Not implemented. (Mac OS, MPE/iX, VMS, RISC OS)
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 (Windows NT and Windows 2000) under NTFS only.
localtime
Because Perl currently relies on the native standard C localtime() function, it is only safe
to use times between 0 and (2**31)-1. Times outside this range may result in unexpected
behavior depending on your operating system's implementation of localtime().
lstat Not implemented. (VMS, RISC OS)
Return values (especially for device and inode) may be bogus. (Win32)
msgctl
msgget
msgsnd
msgrcv Not implemented. (Mac OS, Win32, VMS, Plan 9, RISC OS, VOS)
open The "|" variants are supported only if ToolServer is installed. (Mac OS)
open to "|-" and "-|" are unsupported. (Mac OS, Win32, RISC OS)
Opening a process does not automatically flush output handles on some platforms. (SunOS,
Solaris, HP-UX)
pipe Very limited functionality. (MiNT)
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. (Mac OS, Win32, VMS, RISC OS, VOS)
setgrent
Not implemented. (Mac OS, MPE/iX, VMS, Win32, RISC OS)
setpgrp Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)
setpriority
Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)
setpwent
Not implemented. (Mac OS, MPE/iX, Win32, RISC OS)
setsockopt
Not implemented. (Plan 9)
shmctl
shmget
shmread
shmwrite
Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)
sockatmark
A relatively recent addition to socket functions, may not be implemented even in UNIX plat-forms. platforms.
forms.
socketpair
Not implemented. (Win32, VMS, RISC OS, VOS, VM/ESA)
stat Platforms that do not have rdev, blksize, or blocks will return these as '', so numeric com-parison comparison
parison or manipulation of these fields may cause 'not numeric' warnings.
mtime and atime are the same thing, and ctime is creation time instead of inode change time.
(Mac OS).
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 nec-essarily necessarily
essarily 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)
symlink Not implemented. (Win32, VMS, RISC OS)
syscall Not implemented. (Mac OS, 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 In general, do not assume the UNIX/POSIX semantics that you can shift $? right by eight to
get the exit value, or that "$? & 127" would give you the number of the signal that termi-nated terminated
nated the program, or that "$? & 128" would test true if the program was terminated by a
coredump. Instead, use the POSIX W*() interfaces: for example, use WIFEXITED($?) and WEXIT-VALUE($?) WEXITVALUE($?)
VALUE($?) to test for a normal exit and the exit value, WIFSIGNALED($?) and WTERMSIG($?) for
a signal exit and the signal. Core dumping is not a portable concept, so there's no portable
way to test for that.
Only implemented if ToolServer is installed. (Mac OS)
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 compati-ble compatible
ble 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)
Far from being POSIX compliant. Because there may be no underlying /bin/sh tries to work
around the problem by forking and execing the first token in its argument string. Handles
basic redirection ("<" or ">") on its own behalf. (MiNT)
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'"). For more details see "$?" in perlvms. (VMS)
times Only the first entry returned is nonzero. (Mac OS)
"cumulative" times will be bogus. On anything other than Windows NT or Windows 2000, "sys-tem" "system"
tem" time will be bogus, and "user" time is actually the time returned by the clock() func-tion function
tion in the C runtime library. (Win32)
Not useful. (RISC OS)
truncate
Not implemented. (Older versions of VMS)
Truncation to zero-length 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. (Ami-gaOS) (AmigaOS)
gaOS)
utime Only the modification time is updated. (BeOS, Mac OS, 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 Not implemented. (Mac OS, VOS)
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
As of September 2003 (the Perl release 5.8.1), the following platforms are able to build Perl from
the standard source code distribution available at http://www.cpan.org/src/index.html
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
LynxOS
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)
SVR4
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 5.8.1 release. There is a very good chance that many of
these will work fine with the 5.8.1.
DomainOS
Hurd
MachTen
PowerMAX
SCO SV
Unixware
Windows 3.1
Known to be broken for 5.8.0 and 5.8.1 (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 hard-
ware/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 perlbug@perl.org 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
MiNT
MPC
NEWS-OS
NextSTEP
OpenSTEP
Opus
Plan 9
RISC/os
SCO ODT/OSR
Stellar
SVR2
TI1500
TitanOS
Ultrix
Unisys Dynix
The following platforms have their own source code distributions and binaries available via
http://www.cpan.org/ports/
Perl release
OS/400 (ILE) 5.005_02
Tandem Guardian 5.004
The following platforms have only binaries available via http://www.cpan.org/ports/index.html :
Perl release
Acorn RISCOS 5.005_02
AOS 5.002
LynxOS 5.004_02
Although we do suggest that you always build your own Perl from the source code, both for maximal
configurability and for security, in case you are in a hurry you can check
http://www.cpan.org/ports/index.html for binary distributions.
SEE ALSO
perlaix, perlamiga, perlapollo, perlbeos, perlbs2000, perlce, perlcygwin, perldgux, perldos, per-
lepoc, perlebcdic, perlfreebsd, perlhurd, perlhpux, perlirix, perlmachten, perlmacos, perlmacosx,
perlmint, perlmpeix, perlnetware, perlos2, perlos390, perlos400, perlplan9, perlqnx, perlsolaris,
perltru64, perlunicode, perlvmesa, perlvms, perlvos, perlwin32, and Win32.
AUTHORS / CONTRIBUTORS
Abigail <abigail@foad.org>, 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@com-
puter.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. Koenig
<a.koenig@mind.de>, Markus Laker <mlaker@contax.co.uk>, Andrew M. Langmead <aml@world.std.com>, 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>, Andre 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>.
perl v5.8.8 2006-01-07 PERLPORT(1)
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