perlport - Writing portable Perl
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:
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.
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 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">).
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 commonly 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 the Dunce::Files manpage 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 $/ to the appropriate value for your file format before using chomp().
Because of the ``text'' mode translation, DOSish perls have limitations
in using seek and tell on a file accessed in ``text'' mode.
Stick to seek-ing to locations you got from tell (and no
others), and you are usually free to use seek and tell even
in ``text'' mode. Using seek or tell or other file operations
may be non-portable. If you use binmode on a file, however, you
can usually seek and tell with arbitrary values in safety.
A common misconception in socket programming is that \n eq \012
everywhere. When using protocols such as common Internet protocols,
\012 and \015 are called for specifically, and the values of
the logical \n and \r (carriage return) are not reliable.
print SOCKET "Hi there, client!\r\n"; # WRONG
print SOCKET "Hi there, client!\015\012"; # RIGHT
However, using \015\012 (or \cM\cJ, or \x0D\x0A) can be tedious
and unsightly, as well as confusing to those maintaining the code. As
such, the Socket module supplies the Right Thing for those who want it.
use Socket qw(:DEFAULT :crlf);
print SOCKET "Hi there, client!$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).
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
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 guaranteed 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 precisely UTF-EBCDIC will go.
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 interfaces like chmod() work, but sometimes
there simply is no good mapping.
If all this is intimidating, have no (well, maybe only a little) fear. There are modules that can help. The File::Spec modules provide methods to do the Right Thing on whatever platform happens to be running the program.
use File::Spec::Functions;
chdir(updir()); # go up one directory
$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 contain the encrypted passwords, because the system is using some form of enhanced security. Or it may not contain all the accounts, because the system is using NIS. If code does need to rely on such a file, include a description of the file and its format in the code's documentation, then make it easy for the user to override the default location of the file.
Don't assume a text file will end with a newline. They should, but people forget.
Do not have two files or directories of the same name with different
case, like test.pl and Test.pl, as many platforms have
case-insensitive (or at least case-forgiving) filenames. Also, try
not to have non-word characters (except for .) in the names, and
keep them to the 8.3 convention, for maximum portability, onerous a
burden though this may appear.
Likewise, when using the AutoSplit module, try to keep your functions to 8.3 naming and case-insensitive conventions; or, at the least, make it so the resulting files have a unique (case-insensitively) first 8 characters.
Whitespace in filenames is tolerated on most systems, but not all, and even on systems where it might be tolerated, some utilities might become confused by such whitespace.
Many systems (DOS, VMS) 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.)
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.
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.
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;
$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;}
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 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 professional.
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 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).
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.
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.
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.
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.
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 ä comes before ``b''.
If you may assume POSIX (a rather large assumption), you may read more about the POSIX locale system from the perllocale manpage. 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 the perluniintro manpage and the perlunicode manpage 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.
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.
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.)
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.
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/
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.
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.
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 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:
OS $^O $Config{archname} ID Version
--------------------------------------------------------
MS-DOS dos ?
PC-DOS dos ?
OS/2 os2 ?
Windows 3.1 ? ? 0 3 01
Windows 95 MSWin32 MSWin32-x86 1 4 00
Windows 98 MSWin32 MSWin32-x86 1 4 10
Windows ME MSWin32 MSWin32-x86 1 ?
Windows NT MSWin32 MSWin32-x86 2 4 xx
Windows NT MSWin32 MSWin32-ALPHA 2 4 xx
Windows NT MSWin32 MSWin32-ppc 2 4 xx
Windows 2000 MSWin32 MSWin32-x86 2 5 00
Windows XP MSWin32 MSWin32-x86 2 5 01
Windows 2003 MSWin32 MSWin32-x86 2 5 02
Windows CE MSWin32 ? 3
Cygwin cygwin cygwin
The various MSWin32 Perl's can distinguish the OS they are running on via the value of the fifth element of the list returned from Win32::GetOSVersion(). For example:
if ($^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:
The djgpp environment for DOS, http://www.delorie.com/djgpp/ and the perldos manpage.
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 the perlos2 manpage.
Build instructions for Win32 in the perlwin32 manpage, or under the Cygnus environment in the perlcygwin manpage.
The Win32::* modules in Win32.
The ActiveState Pages, http://www.activestate.com/
The Cygwin environment for Win32; README.cygwin (installed as the perlcygwin manpage), http://www.cygwin.com/
The U/WIN environment for Win32, http://www.research.att.com/sw/tools/uwin/
Build instructions for OS/2, the perlos2 manpage
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 distributed 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/
Perl on VMS is discussed in the perlvms manpage 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 $read = <STDIN>;.
Filenames are in the format ``name.extension;version''. The maximum
length for filenames is 39 characters, and the maximum length for
extensions is also 39 characters. Version is a number from 1 to
32767. Valid characters are /[A-Z0-9$_-]/.
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), the perlvms manpage
vmsperl list, majordomo@perl.org
(Put the words subscribe vmsperl in message body.)
vmsperl on the web, http://www.sidhe.org/vmsperl/index.html
Perl on VOS is discussed in README.vos in the perl distribution (installed as the perlvos manpage). 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 contain 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 runtime. 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 the perlvos manpage) 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 the perlvos manpage)
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
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 the perlos390 manpage 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 the perlos400 manpage.
As of R2.5 of USS for OS/390 and Version 2.3 of VM/ESA these Unix
sub-systems do not support the #! shebang trick for script invocation.
Hence, on OS/390 and VM/ESA perl scripts can be executed with a header
similar to the following simple script:
: # use perl
eval 'exec /usr/local/bin/perl -S $0 ${1+"$@"}'
if 0;
#!/usr/local/bin/perl # just a comment really
print "Hello from perl!\n";
OS/390 will support the #! shebang trick in release 2.8 and beyond.
Calls to system and backticks can use POSIX shell syntax on all
S/390 systems.
On the AS/400, if PERL5 is in your library list, you may need to wrap your perl scripts in a CL procedure to invoke them like so:
BEGIN
CALL PGM(PERL5/PERL) PARM('/QOpenSys/hello.pl')
ENDPGM
This will invoke the perl script hello.pl in the root of the
QOpenSys file system. On the AS/400 calls to system or backticks
must use CL syntax.
On these platforms, bear in mind that the EBCDIC character set may have
an effect on what happens with some perl functions (such as chr,
pack, print, printf, ord, sort, sprintf, unpack), as
well as bit-fiddling with ASCII constants using operators like ^, &
and |, not to mention dealing with socket interfaces to ASCII computers
(see Newlines).
Fortunately, most web servers for the mainframe will correctly
translate the \n in the following statement to its ASCII equivalent
(\r is the same under both Unix and 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 $Config{'archname'}
--------------------------------------------
OS/390 os390 os390
OS400 os400 os400
POSIX-BC posix-bc BS2000-posix-bc
VM/ESA vmesa vmesa
Some simple tricks for determining if you are running on an EBCDIC platform could include any of the following (perhaps all):
if ("\t" eq "\05") { print "EBCDIC may be spoken here!\n"; }
if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; }
if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; }
One thing you may not want to rely on is the EBCDIC encoding of punctuation characters since these may differ from code page to code page (and once your module or script is rumoured to work with EBCDIC, folks will want it to work with all EBCDIC character sets).
Also see:
the perlos390 manpage, README.os390, perlbs2000, README.vmesa, the perlebcdic manpage.
The perl-mvs@perl.org list is for discussion of porting issues as well as general usage issues for all EBCDIC Perls. Send a message body of ``subscribe perl-mvs'' to majordomo@perl.org.
AS/400 Perl information at http://as400.rochester.ibm.com/ as well as on CPAN in the ports/ directory.
Because Acorns use ASCII with newlines (\n) in text files as \012 like
Unix, and because Unix filename emulation is turned on by default,
most simple scripts will probably work ``out of the box''. The native
filesystem is modular, and individual filesystems are free to be
case-sensitive or insensitive, and are usually case-preserving. Some
native filesystems have name length limits, which file and directory
names are silently truncated to fit. Scripts should be aware that the
standard filesystem currently has a name length limit of 10
characters, with up to 77 items in a directory, but other filesystems
may not impose such limitations.
Native filenames are of the form
Filesystem#Special_Field::DiskName.$.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 $. if scripts are not careful.
Logical paths specified by system variables containing comma-separated
search lists are also allowed; hence System:Modules is a valid
filename, and the filesystem will prefix Modules with each section of
System$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$Name. Each filesystem maintains a current directory,
and the current filesystem's current directory is the global current
directory. Consequently, sociable programs don't change the current
directory but rely on full pathnames, and programs (and Makefiles) cannot
assume that they can spawn a child process which can change the current
directory without affecting its parent (and everyone else for that
matter).
Because native operating system filehandles are global and are currently
allocated down from 255, with 0 being a reserved value, the Unix emulation
library emulates Unix filehandles. Consequently, you can't rely on
passing STDIN, STDOUT, or STDERR to your children.
The desire of users to express filenames of the form
<Foo$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).
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 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:
Amiga, README.amiga (installed as the perlamiga manpage).
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
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.
-r, -w, and -x have a limited meaning only; directories
and applications are executable, 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 meaningless. (Win32)
-x (or -X) determine if a file has an executable file type.
(RISC OS)
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.
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.
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)
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 settings. (Cygwin)
Not implemented. (Mac OS, Win32, Plan 9, RISC OS, VOS)
Does nothing, but won't fail. (Win32)
Not implemented. (Mac OS, Win32, VMS, Plan 9, RISC OS, VOS, VM/ESA)
May not be available if library or source was not provided when building perl. (Win32)
Not implemented. (VOS)
Not implemented. (VMS, Plan 9, VOS)
Not implemented. (VMS, Plan 9, VOS)
Not useful. (Mac OS, RISC OS)
Not implemented. (Win32)
Invokes VMS debugger. (VMS)
Not implemented. (Mac OS)
Implemented via Spawn. (VM/ESA)
Does not automatically flush output handles on some platforms. (SunOS, Solaris, HP-UX)
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)
Not implemented. (Win32, VMS)
Not implemented (Mac OS, VMS, RISC OS, VOS).
Available only on Windows NT (not on Windows 95). (Win32)
Not implemented. (Mac OS, AmigaOS, RISC OS, VOS, VM/ESA, VMS)
Emulated using multiple interpreters. See the perlfork manpage. (Win32)
Does not automatically flush output handles on some platforms. (SunOS, Solaris, HP-UX)
Not implemented. (Mac OS, RISC OS)
Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)
Not implemented. (Mac OS, Win32, RISC OS)
Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS, VM/ESA)
Not implemented. (Mac OS, Win32)
Not useful. (RISC OS)
Not implemented. (Mac OS, Win32, VMS, RISC OS)
Not implemented. (Mac OS, Win32, Plan 9)
Not implemented. (Mac OS, Win32)
Not useful. (RISC OS)
Not implemented. (Mac OS, Win32, VMS, RISC OS)
Not implemented. (Mac OS, Win32, Plan 9)
Not implemented. (Mac OS)
Not implemented. (Mac OS)
Not implemented. (Mac OS, Win32, VM/ESA)
Not implemented. (Mac OS, Win32, VMS, VM/ESA)
gethostbyname('localhost') does not work everywhere: you may have
to use gethostbyname('127.0.0.1'). (Mac OS, Irix 5)
Not implemented. (Mac OS, Win32)
Not implemented. (Mac OS, Win32, Plan 9)
Not implemented. (Mac OS, Win32, Plan 9)
Not implemented. (Win32, Plan 9)
Not implemented. (Mac OS, Win32, Plan 9, RISC OS)
Not implemented. (Mac OS, Win32, Plan 9, RISC OS)
Not implemented. (Mac OS, Win32, Plan 9, RISC OS)
Not implemented. (Plan 9, Win32, RISC OS)
Not implemented. (Mac OS, MPE/iX, VM/ESA, Win32)
Not implemented. (Mac OS, MPE/iX, RISC OS, VM/ESA, VMS, Win32)
Not implemented. (Mac OS, Win32)
Not implemented. (Mac OS, Win32, Plan 9)
Not implemented. (Mac OS, Win32, Plan 9)
Not implemented. (Plan 9, Win32)
Not implemented. (Plan 9)
This operator is implemented via the File::Glob extension on most platforms. See the File::Glob manpage for portability information.
Same portability caveats as localtime.
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(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 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)
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.
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().
Not implemented. (VMS, RISC OS)
Return values (especially for device and inode) may be bogus. (Win32)
Not implemented. (Mac OS, Win32, VMS, Plan 9, RISC OS, VOS)
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)
Very limited functionality. (MiNT)
Not implemented. (Win32, VMS, RISC OS)
Can't move directories between directories on different logical volumes. (Win32)
Only implemented on sockets. (Win32, VMS)
Only reliable on sockets. (RISC OS)
Note that the select FILEHANDLE form is generally portable.
Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)
Not implemented. (Mac OS, MPE/iX, VMS, Win32, RISC OS)
Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)
Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)
Not implemented. (Mac OS, MPE/iX, Win32, RISC OS)
Not implemented. (Plan 9)
Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)
A relatively recent addition to socket functions, may not be implemented even in UNIX platforms.
Not implemented. (Win32, VMS, RISC OS, VOS, VM/ESA)
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.
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 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)
Not implemented. (Win32, VMS, RISC OS)
Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS, VM/ESA)
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)
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 terminated 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 WEXITVALUE($?) to test for a normal exit and the exit
value, WIFSIGNALED($?) 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 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)
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 the perlvms manpage. (VMS)
Only the first entry returned is nonzero. (Mac OS)
``cumulative'' times will be bogus. On anything other than Windows NT
or Windows 2000, ``system'' time will be bogus, and ``user'' time is
actually the time returned by the clock() function in the C runtime
library. (Win32)
Not useful. (RISC OS)
Not implemented. (Older versions of VMS)
Truncation to 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)
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)
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)
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)
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 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 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.
the perlaix manpage, the perlamiga manpage, the perlapollo manpage, the perlbeos manpage, the perlbs2000 manpage, the perlce manpage, the perlcygwin manpage, the perldgux manpage, the perldos manpage, the perlepoc manpage, the perlebcdic manpage, the perlfreebsd manpage, the perlhurd manpage, the perlhpux manpage, the perlirix manpage, the perlmachten manpage, the perlmacos manpage, the perlmacosx manpage, the perlmint manpage, the perlmpeix manpage, the perlnetware manpage, the perlos2 manpage, the perlos390 manpage, the perlos400 manpage, the perlplan9 manpage, the perlqnx manpage, the perlsolaris manpage, the perltru64 manpage, the perlunicode manpage, the perlvmesa manpage, the perlvms manpage, the perlvos manpage, the perlwin32 manpage, and Win32.
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@computer.org>, Neale Ferguson <neale@vma.tabnsw.com.au>, David J. Fiander <davidf@mks.com>, Paul Green <Paul_Green@stratus.com>, M.J.T. Guy <mjtg@cam.ac.uk>, Jarkko Hietaniemi <jhi@iki.fi>, Luther Huffman <lutherh@stratcom.com>, Nick Ing-Simmons <nick@ing-simmons.net>, Andreas J. König <a.koenig@mind.de>, Markus Laker <mlaker@contax.co.uk>, Andrew M. Langmead <aml@world.std.com>, Larry Moore <ljmoore@freespace.net>, Paul Moore <Paul.Moore@uk.origin-it.com>, Chris Nandor <pudge@pobox.com>, Matthias Neeracher <neeracher@mac.com>, Philip Newton <pne@cpan.org>, Gary Ng <71564.1743@CompuServe.COM>, Tom Phoenix <rootbeer@teleport.com>, André Pirard <A.Pirard@ulg.ac.be>, Peter Prymmer <pvhp@forte.com>, Hugo van der Sanden <hv@crypt0.demon.co.uk>, Gurusamy Sarathy <gsar@activestate.com>, Paul J. Schinder <schinder@pobox.com>, Michael G Schwern <schwern@pobox.com>, Dan Sugalski <dan@sidhe.org>, Nathan Torkington <gnat@frii.com>.