| perlport - Writing portable Perl |
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 has the full generality of being portable, or whether to just get the job done right now. This is the hardest choice to be made. The rest is easy, because Perl provides many choices, whichever way you want to approach your problem.
Looking at it another way, writing portable code is usually about willfully limiting your available choices. Naturally, it takes discipline and sacrifice to do that. The product of portability and convenience may be a constant. You have been warned.
Be aware of two important points:
Here's the general rule: When you approach a task commonly done using a whole range of platforms, think about writing portable code. That way, you don't sacrifice much by way of the implementation choices you can avail yourself of, and at the same time you can give your users lots of platform choices. On the other hand, when you have to take advantage of some unique feature of a particular platform, as is often the case with systems programming (whether for Unix, Windows, VMS, etc.), consider writing platform-specific code.
When the code will run on only two or three operating systems, you may need to consider only the differences of those particular systems. The important thing is to decide where the code will run and to be deliberate in your decision.
The material below is separated into three main sections: main issues of portability (ISSUES), platform-specific issues (PLATFORMS), and built-in Perl functions that behave differently on various ports (FUNCTION IMPLEMENTATIONS).
This information should not be considered complete; it includes possibly
transient information about idiosyncrasies of some of the ports, almost
all of which are in a state of constant evolution. Thus, this material
should be considered a perpetual work in progress
(<IMG SRC="yellow_sign.gif" ALT="Under Construction">).
In most operating systems, lines in files are terminated by newlines.
Just what is used as a newline may vary from OS to OS. Unix
traditionally uses \012, one type of DOSish I/O uses \015\012,
Mac OS uses \015, and z/OS uses \025.
Perl uses \n to represent the ``logical'' newline, where what is
logical may depend on the platform in use. In MacPerl, \n always
means \015. On EBCDIC platforms, \n could be \025 or \045.
In DOSish perls, \n usually means \012, but when
accessing a file in ``text'' mode, perl uses the :crlf layer that
translates it to (or from) \015\012, depending on whether you're
reading or writing. Unix does the same thing on ttys in canonical
mode. \015\012 is commonly referred to as CRLF.
To trim trailing newlines from text lines use
chomp. With default settings that function
looks for a trailing \n character and thus trims in a portable way.
When dealing with binary files (or text files in binary mode) be sure
to explicitly set $/>|perlvar/$sol to the appropriate value for
your file format before using chomp.
Because of the ``text'' mode translation, DOSish perls have limitations in
using seek and
tell on a file accessed in ``text'' mode.
Stick to seek-ing to
locations you got from tell (and no
others), and you are usually free to use
seek and
tell even in ``text'' mode. Using
seek or
tell or other file operations may be
non-portable. If you use binmode on a
file, however, you can usually
seek and
tell with arbitrary values safely.
A common misconception in socket programming is that \n eq \012
everywhere. When using protocols such as common Internet protocols,
\012 and \015 are called for specifically, and the values of
the logical \n and \r (carriage return) are not reliable.
print $socket "Hi there, client!\r\n"; # WRONG
print $socket "Hi there, client!\015\012"; # RIGHT
However, using \015\012 (or \cM\cJ, or \x0D\x0A) can be tedious
and unsightly, as well as confusing to those maintaining the code. As
such, the Socket module supplies the Right Thing for those
who want it.
use Socket qw(:DEFAULT :crlf);
print $socket "Hi there, client!$CRLF" # RIGHT
When reading from a socket, remember that the default input record
separator $/>|perlvar/$sol is \n, but robust socket code
will recognize as either \012 or \015\012 as end of line:
while (<$socket>) { # NOT ADVISABLE!
# ...
}
Because both CRLF and LF end in LF, the input record separator can be set to LF and any CR stripped later. Better to write:
use Socket qw(:DEFAULT :crlf);
local($/) = LF; # not needed if $/ is already \012
while (<$socket>) {
s/$CR?$LF/\n/; # not sure if socket uses LF or CRLF, OK
# s/\015?\012/\n/; # same thing
}
This example is preferred over the previous one--even for Unix
platforms--because now any \015's (\cM's) are stripped out
(and there was much rejoicing).
Similarly, functions that return text data--such as a function that fetches a web page--should sometimes translate newlines before returning the data, if they've not yet been translated to the local newline representation. A single line of code will often suffice:
$data =~ s/\015?\012/\n/g;
return $data;
Some of this may be confusing. Here's a handy reference to the ASCII CR and LF characters. You can print it out and stick it in your wallet.
LF eq \012 eq \x0A eq \cJ eq chr(10) eq ASCII 10
CR eq \015 eq \x0D eq \cM eq chr(13) eq ASCII 13
| Unix | DOS | Mac |
---------------------------
\n | LF | LF | CR |
\r | CR | CR | LF |
\n * | LF | CRLF | CR |
\r * | CR | CR | LF |
---------------------------
* text-mode STDIO
The Unix column assumes that you are not accessing a serial line (like a tty) in canonical mode. If you are, then CR on input becomes ``\n'', and ``\n'' on output becomes CRLF.
These are just the most common definitions of \n and \r in Perl.
There may well be others. For example, on an EBCDIC implementation
such as z/OS (OS/390) or OS/400 (using the ILE, the PASE is ASCII-based)
the above material is similar to ``Unix'' but the code numbers change:
LF eq \025 eq \x15 eq \cU eq chr(21) eq CP-1047 21
LF eq \045 eq \x25 eq chr(37) eq CP-0037 37
CR eq \015 eq \x0D eq \cM eq chr(13) eq CP-1047 13
CR eq \015 eq \x0D eq \cM eq chr(13) eq CP-0037 13
| z/OS | OS/400 |
----------------------
\n | LF | LF |
\r | CR | CR |
\n * | LF | LF |
\r * | CR | CR |
----------------------
* text-mode STDIO
Different CPUs store integers and floating point numbers in different orders (called endianness) and widths (32-bit and 64-bit being the most common today). This affects your programs when they attempt to transfer numbers in binary format from one CPU architecture to another, usually either ``live'' via network connection, or by storing the numbers to secondary storage such as a disk file or tape.
Conflicting storage orders make an utter mess out of the numbers. If a
little-endian host (Intel, VAX) stores 0x12345678 (305419896 in
decimal), a big-endian host (Motorola, Sparc, PA) reads it as
0x78563412 (2018915346 in decimal). Alpha and MIPS can be either:
Digital/Compaq used/uses them in little-endian mode; SGI/Cray uses
them in big-endian mode. To avoid this problem in network (socket)
connections use the pack and
unpack formats n and N, the
``network'' orders. These are guaranteed to be portable.
As of Perl 5.10.0, you can also use the > and < modifiers
to force big- or little-endian byte-order. This is useful if you want
to store signed integers or 64-bit integers, for example.
You can explore the endianness of your platform by unpacking a data structure packed in native format such as:
print unpack("h*", pack("s2", 1, 2)), "\n";
# '10002000' on e.g. Intel x86 or Alpha 21064 in little-endian mode
# '00100020' on e.g. Motorola 68040
If you need to distinguish between endian architectures you could use either of the variables set like so:
$is_big_endian = unpack("h*", pack("s", 1)) =~ /01/;
$is_little_endian = unpack("h*", pack("s", 1)) =~ /^1/;
Differing widths can cause truncation even between platforms of equal endianness. The platform of shorter width loses the upper parts of the number. There is no good solution for this problem except to avoid transferring or storing raw binary numbers.
One can circumnavigate both these problems in two ways. Either
transfer and store numbers always in text format, instead of raw
binary, or else consider using modules like
Data::Dumper and Storable (included as
of Perl 5.8). Keeping all data as text significantly simplifies matters.
Most platforms these days structure files in a hierarchical fashion. So, it is reasonably safe to assume that all platforms support the notion of a ``path'' to uniquely identify a file on the system. How that path is really written, though, differs considerably.
Although similar, file path specifications differ between Unix, Windows, Mac OS, OS/2, VMS, VOS, RISC OS, and probably others. Unix, for example, is one of the few OSes that has the elegant idea of a single root directory.
DOS, OS/2, VMS, VOS, and Windows can work similarly to Unix with /
as path separator, or in their own idiosyncratic ways (such as having
several root directories and various ``unrooted'' device files such NIL:
and LPT:).
Mac OS 9 and earlier used : as a path separator instead of /.
The filesystem may support neither hard links
(link) nor symbolic links
(symlink,
readlink,
lstat).
The filesystem may support neither access timestamp nor change timestamp (meaning that about the only portable timestamp is the modification timestamp), or one second granularity of any timestamps (e.g. the FAT filesystem limits the time granularity to two seconds).
The ``inode change timestamp'' (the -C
filetest) may really be the ``creation timestamp'' (which it is not in
Unix).
VOS perl can emulate Unix filenames with / as path separator. The
native pathname characters greater-than, less-than, number-sign, and
percent-sign are always accepted.
RISC OS perl can emulate Unix filenames with / as path
separator, or go native and use . for path separator and : to
signal filesystems and disk names.
Don't assume Unix filesystem access semantics: that read, write,
and execute are all the permissions there are, and even if they exist,
that their semantics (for example what do r, w, and x mean on
a directory) are the Unix ones. The various Unix/POSIX compatibility
layers usually try to make interfaces like chmod
work, but sometimes there simply is no good mapping.
The File::Spec modules provide methods to manipulate path
specifications and return the results in native format for each
platform. This is often unnecessary as Unix-style paths are
understood by Perl on every supported platform, but if you need to
produce native paths for a native utility that does not understand
Unix syntax, or if you are operating on paths or path components
in unknown (and thus possibly native) syntax, File::Spec
is your friend. Here are two brief examples:
use File::Spec::Functions;
chdir(updir()); # go up one directory
# Concatenate a path from its components
my $file = catfile(updir(), 'temp', 'file.txt');
# on Unix: '../temp/file.txt'
# on Win32: '..\temp\file.txt'
# on VMS: '[-.temp]file.txt'
In general, production code should not have file paths hardcoded. Making them user-supplied or read from a configuration file is better, keeping in mind that file path syntax varies on different machines.
This is especially noticeable in scripts like Makefiles and test suites,
which often assume / as a path separator for subdirectories.
Also of use is File::Basename from the standard
distribution, which splits a pathname into pieces (base filename, full
path to directory, and file suffix).
Even when on a single platform (if you can call Unix a single platform), remember not to count on the existence or the contents of particular system-specific files or directories, like /etc/passwd, /etc/sendmail.conf, /etc/resolv.conf, or even /tmp/. For example, /etc/passwd may exist but not contain the encrypted passwords, because the system is using some form of enhanced security. Or it may not contain all the accounts, because the system is using NIS. If code does need to rely on such a file, include a description of the file and its format in the code's documentation, then make it easy for the user to override the default location of the file.
Don't assume a text file will end with a newline. They should, but people forget.
Do not have two files or directories of the same name with different
case, like test.pl and Test.pl, as many platforms have
case-insensitive (or at least case-forgiving) filenames. Also, try
not to have non-word characters (except for .) in the names, and
keep them to the 8.3 convention, for maximum portability, onerous a
burden though this may appear.
Likewise, when using the AutoSplit module, try to keep
your functions to 8.3 naming and case-insensitive conventions; or, at the
least, make it so the resulting files have a unique (case-insensitively)
first 8 characters.
Whitespace in filenames is tolerated on most systems, but not all, and even on systems where it might be tolerated, some utilities might become confused by such whitespace.
Many systems (DOS, VMS ODS-2) cannot have more than one . in their
filenames.
Don't assume > won't be the first character of a filename.
Always use the three-arg version of
open:
open my $fh, '<', $existing_file) or die $!;
Two-arg open is magic and can
translate characters like >, <, and | in filenames,
which is usually the wrong thing to do.
sysopen and three-arg
open don't have this problem.
Don't use : as a part of a filename since many systems use that for
their own semantics (Mac OS Classic for separating pathname components,
many networking schemes and utilities for separating the nodename and
the pathname, and so on). For the same reasons, avoid @, ; and
|.
Don't assume that in pathnames you can collapse two leading slashes
// into one: some networking and clustering filesystems have special
semantics for that. Let the operating system sort it out.
The portable filename characters as defined by ANSI C are
a b c d e f g h i j k l m n o p q r s t u v w x y z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 0 1 2 3 4 5 6 7 8 9 . _ -
and - shouldn't be the first character. If you want to be
hypercorrect, stay case-insensitive and within the 8.3 naming
convention (all the files and directories have to be unique within one
directory if their names are lowercased and truncated to eight
characters before the ., if any, and to three characters after the
., if any). (And do not use .s in directory names.)
Not all platforms provide a command line. These are usually platforms that rely primarily on a Graphical User Interface (GUI) for user interaction. A program requiring a command line interface might not work everywhere. This is probably for the user of the program to deal with, so don't stay up late worrying about it.
Some platforms can't delete or rename files held open by the system,
this limitation may also apply to changing filesystem metainformation
like file permissions or owners. Remember to
close files when you are done with them.
Don't unlink or
rename an open file. Don't
tie or
open a file already tied or opened;
untie or
close it first.
Don't open the same file more than once at a time for writing, as some operating systems put mandatory locks on such files.
Don't assume that write/modify permission on a directory gives the right to add or delete files/directories in that directory. That is filesystem specific: in some filesystems you need write/modify permission also (or even just) in the file/directory itself. In some filesystems (AFS, DFS) the permission to add/delete directory entries is a completely separate permission.
Don't assume that a single unlink completely
gets rid of the file: some filesystems (most notably the ones in VMS) have
versioned filesystems, and unlink removes only
the most recent one (it doesn't remove all the versions because by default
the native tools on those platforms remove just the most recent version,
too). The portable idiom to remove all the versions of a file is
1 while unlink "file";
This will terminate if the file is undeletable for some reason (protected, not there, and so on).
Don't count on a specific environment variable existing in
%ENV. Don't count on %ENV entries
being case-sensitive, or even case-preserving. Don't try to clear
%ENV by saying %ENV = ();, or, if you really have
to, make it conditional on $^O ne 'VMS' since in VMS the
%ENV table is much more than a per-process key-value
string table.
On VMS, some entries in the %ENV hash are dynamically
created when their key is used on a read if they did not previously
exist. The values for $ENV{HOME}, $ENV{TERM}, $ENV{PATH}, and
$ENV{USER}, are known to be dynamically generated. The specific names
that are dynamically generated may vary with the version of the C library
on VMS, and more may exist than are documented.
On VMS by default, changes to the %ENV hash persist
after perl exits. Subsequent invocations of perl in the same process can
inadvertently inherit environment settings that were meant to be
temporary.
Don't count on signals or %SIG for anything.
Don't count on filename globbing. Use
opendir,
readdir, and
closedir instead.
Don't count on per-program environment variables, or per-program current directories.
Don't count on specific values of $!, neither numeric nor
especially the string values. Users may switch their locales causing
error messages to be translated into their languages. If you can
trust a POSIXish environment, you can portably use the symbols defined
by the Errno module, like ENOENT. And don't trust on the
values of $! at all except immediately after a failed
system call.
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 $Config{_exe}>|Config/_exe in the
Config module holds the executable suffix, if any. Third,
the VMS port carefully sets up $^X and
$Config{perlpath}>|Config/perlpath so that no further processing
is required. This is just as well, because the matching regular
expression used below would then have to deal with a possible trailing
version number in the VMS file name.
To convert $^X to a file pathname, taking account of
the requirements of the various operating system possibilities, say:
use Config;
my $thisperl = $^X;
if ($^O ne 'VMS') {
$thisperl .= $Config{_exe}
unless $thisperl =~ m/\Q$Config{_exe}\E$/i;
}
To convert $Config{perlpath}>|Config/perlpath to a file pathname, say:
use Config;
my $thisperl = $Config{perlpath};
if ($^O ne 'VMS') {
$thisperl .= $Config{_exe}
unless $thisperl =~ m/\Q$Config{_exe}\E$/i;
}
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
ioctls will work.
Don't assume that you can ping hosts and get replies.
Don't assume that any particular port (service) will respond.
Don't assume that Sys::Hostname (or any other API or
command) returns either a fully qualified hostname or a non-qualified
hostname: it all depends on how the system had been configured. Also
remember that for things such as DHCP and NAT, the hostname you get back
might not be very useful.
All the above don'ts may look daunting, and they are, but the key is to degrade gracefully if one cannot reach the particular network service one wants. Croaking or hanging do not look very professional.
In general, don't directly access the system in code meant to be
portable. That means, no system,
exec, fork,
pipe,
``> or qx//|perlop/qx/STRING/,
open with a |, nor any of the other
things that makes being a Perl hacker worth being.
Commands that launch external processes are generally supported on
most platforms (though many of them do not support any type of
forking). The problem with using them arises from what you invoke
them on. External tools are often named differently on different
platforms, may not be available in the same location, might accept
different arguments, can behave differently, and often present their
results in a platform-dependent way. Thus, you should seldom depend
on them to produce consistent results. (Then again, if you're calling
netstat -a, you probably don't expect it to run on both Unix and CP/M.)
One especially common bit of Perl code is opening a pipe to sendmail:
open(my $mail, '|-', '/usr/lib/sendmail -t')
or die "cannot fork sendmail: $!";
This is fine for systems programming when sendmail is known to be
available. But it is not fine for many non-Unix systems, and even
some Unix systems that may not have sendmail installed. If a portable
solution is needed, see the various distributions on CPAN that deal
with it. Mail::Mailer and Mail::Send
in the MailTools distribution are commonly used, and provide several
mailing methods, including mail, sendmail, and direct SMTP (via
Net::SMTP) if a mail transfer agent is not available.
Mail::Sendmail is a standalone module that provides
simple, platform-independent mailing.
The Unix System V IPC (msg*(), sem*(), shm*()) is not available
even on all Unix platforms.
Do not use either the bare result of pack("N", 10, 20, 30, 40) or
bare v-strings (such as v10.20.30.40) to represent IPv4 addresses:
both forms just pack the four bytes into network order. That this
would be equal to the C language in_addr struct (which is what the
socket code internally uses) is not guaranteed. To be portable use
the routines of the Socket module, such as
inet_aton,
inet_ntoa, and
sockaddr_in.
The rule of thumb for portable code is: Do it all in portable Perl, or use a module (that may internally implement it with platform-specific code, but exposes a common interface).
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
NDBM_File and DB_File are available.
The good news is that at least some DBM module should be available, and
AnyDBM_File will use whichever module it can find. Of
course, then the code needs to be fairly strict, dropping to the greatest
common factor (e.g., not exceeding 1K for each record), so that it will
work with any DBM module. See the AnyDBM_File manpage 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 guess what
date 02/03/04 might be. ISO 8601 even sorts nicely as-is.
A text representation (like ``1987-12-18'') can be easily converted
into an OS-specific value using a module like
Time::Piece (see Date Parsing in the Time::Piece manpage) or
Date::Parse. An array of values, such as those
returned by localtime, can be converted to an OS-specific
representation using Time::Local.
When calculating specific times, such as for tests in time or date modules, it may be appropriate to calculate an offset for the epoch.
use Time::Local qw(timegm);
my $offset = timegm(0, 0, 0, 1, 0, 70);
The value for $offset in Unix will be 0, but in Mac OS Classic
will be some large number. $offset can then be added to a Unix time
value to get what should be the proper value on any system.
Assume very little about character sets.
Assume nothing about numerical values (ord,
chr) of characters.
Do not use explicit code point ranges (like \xHH-\xHH). However,
starting in Perl v5.22, regular expression pattern bracketed character
class ranges specified like qr/[\N{U+HH}-\N{U+HH}]/ are portable,
and starting in Perl v5.24, the same ranges are portable in
tr///>|perlop/tr/SEARCHLIST/REPLACEMENTLIST/cdsr.
You can portably use symbolic character classes like [:print:].
Do not assume that the alphabetic characters are encoded contiguously
(in the numeric sense). There may be gaps. Special coding in Perl,
however, guarantees that all subsets of qr/[A-Z]/, qr/[a-z]/, and
qr/[0-9]/ behave as expected.
tr///>|perlop/tr/SEARCHLIST/REPLACEMENTLIST/cdsr
behaves the same for these ranges. In patterns, any ranges specified with
end points using the \N{...} notations ensures character set
portability, but it is a bug in Perl v5.22 that this isn't true of
tr///>|perlop/tr/SEARCHLIST/REPLACEMENTLIST/cdsr,
fixed in v5.24.
Do not assume anything about the ordering of the characters. The lowercase letters may come before or after the uppercase letters; the lowercase and uppercase may be interlaced so that both ``a'' and ``A'' come before ``b''; the accented and other international characters may be interlaced so that ä comes before ``b''. the Unicode::Collate manpage can be used to sort this all out.
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.
By default Perl assumes your source code is written in an 8-bit ASCII
superset. To embed Unicode characters in your strings and regexes, you can
use the \x{HH} or (more portably) \N{U+HH} notations. You can also use the
utf8 pragma and write your code in UTF-8, which lets you use
Unicode characters directly (not just in quoted constructs but also in
identifiers).
If your code is destined for systems with severely constrained (or missing!) virtual memory systems then you want to be especially mindful of avoiding wasteful constructs such as:
my @lines = <$very_large_file>; # bad
while (<$fh>) {$file .= $_} # sometimes bad
my $file = join('', <$fh>); # better
The last two constructs may appear unintuitive to most people. The first repeatedly grows a string, whereas the second allocates a large chunk of memory in one go. On some systems, the second is more efficient than the first.
Most multi-user platforms provide basic levels of security, usually implemented at the filesystem level. Some, however, unfortunately do not. Thus the notion of user id, or ``home'' directory, or even the state of being logged-in, may be unrecognizable on many platforms. If you write programs that are security-conscious, it is usually best to know what type of system you will be running under so that you can write code explicitly for that platform (or class of platforms).
Don't assume the Unix filesystem access semantics: the operating
system or the filesystem may be using some ACL systems, which are
richer languages than the usual rwx. Even if the rwx exist,
their semantics might be different.
(From the security viewpoint, testing for permissions before attempting to do something is silly anyway: if one tries this, there is potential for race conditions. Someone or something might change the permissions between the permissions check and the actual operation. Just try the operation.)
Don't assume the Unix user and group semantics: especially, don't
expect < $< >>|perlvar/$lt and < $> >>|perlvar/$gt (or
$( and $)) to work for switching
identities (or memberships).
Don't assume set-uid and set-gid semantics. (And even if you do, think twice: set-uid and set-gid are a known can of security worms.)
For those times when it is necessary to have platform-specific code,
consider keeping the platform-specific code in one place, making porting
to other platforms easier. Use the Config module and the
special variable $^O to differentiate platforms, as
described in PLATFORMS.
Beware of the ``else syndrome'':
if ($^O eq 'MSWin32') {
# code that assumes Windows
} else {
# code that assumes Linux
}
The else branch should be used for the really ultimate fallback,
not for code specific to some platform.
Be careful in the tests you supply with your module or programs.
Module code may be fully portable, but its tests might not be. This
often happens when tests spawn off other processes or call external
programs to aid in the testing, or when (as noted above) the tests
assume certain things about the filesystem and paths. Be careful not
to depend on a specific output style for errors, such as when checking
$! after a failed system call. Using
$! for anything else than displaying it as output is
doubtful (though see the Errno module for testing reasonably
portably for error value). Some platforms expect a certain output format,
and Perl on those platforms may have been adjusted accordingly. Most
specifically, don't anchor a regex when testing an error value.
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:
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}>|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}>|Config/osname, too) is determined either by
lowercasing and stripping punctuation from the first field of the string
returned by typing uname -a (or a similar command) at the shell prompt
or by testing the file system for the presence of uniquely named files
such as a kernel or header file. Here, for example, are a few of the
more popular Unix flavors:
uname $^O $Config{archname}
--------------------------------------------
AIX aix aix
BSD/OS bsdos i386-bsdos
Darwin darwin darwin
DYNIX/ptx dynixptx i386-dynixptx
FreeBSD freebsd freebsd-i386
Haiku haiku BePC-haiku
Linux linux arm-linux
Linux linux armv5tel-linux
Linux linux i386-linux
Linux linux i586-linux
Linux linux ppc-linux
HP-UX hpux PA-RISC1.1
IRIX irix irix
Mac OS X darwin darwin
NeXT 3 next next-fat
NeXT 4 next OPENSTEP-Mach
openbsd openbsd i386-openbsd
OSF1 dec_osf alpha-dec_osf
reliantunix-n svr4 RM400-svr4
SCO_SV sco_sv i386-sco_sv
SINIX-N svr4 RM400-svr4
sn4609 unicos CRAY_C90-unicos
sn6521 unicosmk t3e-unicosmk
sn9617 unicos CRAY_J90-unicos
SunOS solaris sun4-solaris
SunOS solaris i86pc-solaris
SunOS4 sunos sun4-sunos
Because the value of $Config{archname}>|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:
my $filespec0 = "c:/foo/bar/file.txt";
my $filespec1 = "c:\\foo\\bar\\file.txt";
my $filespec2 = 'c:\foo\bar\file.txt';
my $filespec3 = 'c:\\foo\\bar\\file.txt';
System calls accept either / or \ as the path separator.
However, many command-line utilities of DOS vintage treat / as
the option prefix, so may get confused by filenames containing /.
Aside from calling any external programs, / will work just fine,
and probably better, as it is more consistent with popular usage,
and avoids the problem of remembering what to backwhack and what
not to.
The DOS FAT filesystem can accommodate only ``8.3'' style filenames. Under
the ``case-insensitive, but case-preserving'' HPFS (OS/2) and NTFS (NT)
filesystems you may have to be careful about case returned with functions
like readdir or used with functions like
open or
opendir.
DOS also treats several filenames as special, such as AUX, PRN, NUL, CON, COM1, LPT1, LPT2, etc. Unfortunately, sometimes these filenames won't even work if you include an explicit directory prefix. It is best to avoid such filenames, if you want your code to be portable to DOS and its derivatives. It's hard to know what these all are, unfortunately.
Users of these operating systems may also wish to make use of scripts such as pl2bat.bat to put wrappers around your scripts.
Newline (\n) is translated as \015\012 by the I/O system when
reading from and writing to files (see Newlines).
binmode($filehandle) will keep \n translated as \012 for that
filehandle.
binmode should always be used for code
that deals with binary data. That's assuming you realize in advance that
your data is in binary. General-purpose programs should often assume
nothing about their data.
The $^O variable and the
$Config{archname}>|Config/archname values for various DOSish
perls are as follows:
OS $^O $Config{archname} ID Version
---------------------------------------------------------
MS-DOS dos ?
PC-DOS dos ?
OS/2 os2 ?
Windows 3.1 ? ? 0 3 01
Windows 95 MSWin32 MSWin32-x86 1 4 00
Windows 98 MSWin32 MSWin32-x86 1 4 10
Windows ME MSWin32 MSWin32-x86 1 ?
Windows NT MSWin32 MSWin32-x86 2 4 xx
Windows NT MSWin32 MSWin32-ALPHA 2 4 xx
Windows NT MSWin32 MSWin32-ppc 2 4 xx
Windows 2000 MSWin32 MSWin32-x86 2 5 00
Windows XP MSWin32 MSWin32-x86 2 5 01
Windows 2003 MSWin32 MSWin32-x86 2 5 02
Windows Vista MSWin32 MSWin32-x86 2 6 00
Windows 7 MSWin32 MSWin32-x86 2 6 01
Windows 7 MSWin32 MSWin32-x64 2 6 01
Windows 2008 MSWin32 MSWin32-x86 2 6 01
Windows 2008 MSWin32 MSWin32-x64 2 6 01
Windows CE MSWin32 ? 3
Cygwin cygwin cygwin
The various MSWin32 Perl's can distinguish the OS they are running on
via the value of the fifth element of the list returned from
Win32::GetOSVersion(). For example:
if ($^O eq 'MSWin32') {
my @os_version_info = Win32::GetOSVersion();
print +('3.1','95','NT')[$os_version_info[4]],"\n";
}
There are also Win32::IsWinNT()|Win32/Win32::IsWinNT(),
Win32::IsWin95()|Win32/Win32::IsWin95(), and
Win32::GetOSName(); try
perldoc Win32.
The very portable POSIX::uname()>|POSIX/uname will work too:
c:\> perl -MPOSIX -we "print join '|', uname"
Windows NT|moonru|5.0|Build 2195 (Service Pack 2)|x86
Errors set by Winsock functions are now put directly into $^E,
and the relevant WSAE* error codes are now exported from the
the Errno manpage and the POSIX manpage modules for testing this against.
The previous behavior of putting the errors (converted to POSIX-style
E* error codes since Perl 5.20.0) into $! was buggy due to
the non-equivalence of like-named Winsock and POSIX error constants,
a relationship between which has unfortunately been established
in one way or another since Perl 5.8.0.
The new behavior provides a much more robust solution for checking Winsock errors in portable software without accidentally matching POSIX tests that were intended for other OSes and may have different meanings for Winsock.
The old behavior is currently retained, warts and all, for backwards
compatibility, but users are encouraged to change any code that
tests $! against E* constants for Winsock errors to instead
test $^E against WSAE* constants. After a suitable deprecation
period, which started with Perl 5.24, the old behavior may be
removed, leaving $! unchanged after Winsock function calls, to
avoid any possible confusion over which error variable to check.
Also see:
Win32::* modules in the Win32 manpage.
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
Perl on VMS is discussed in the perlvms manpage in the Perl distribution.
The official name of VMS as of this writing is OpenVMS.
Interacting with Perl from the Digital Command Language (DCL) shell often requires a different set of quotation marks than Unix shells do. For example:
$ perl -e "print ""Hello, world.\n"""
Hello, world.
There are several ways to wrap your Perl scripts in DCL .COM files, if you are so inclined. For example:
$ write sys$output "Hello from DCL!"
$ if p1 .eqs. ""
$ then perl -x 'f$environment("PROCEDURE")
$ else perl -x - 'p1 'p2 'p3 'p4 'p5 'p6 'p7 'p8
$ deck/dollars="__END__"
#!/usr/bin/perl
print "Hello from Perl!\n";
__END__
$ endif
Do take care with $ ASSIGN/nolog/user SYS$COMMAND: SYS$INPUT if your
Perl-in-DCL script expects to do things like $read = <STDIN>;.
The VMS operating system has two filesystems, designated by their on-disk structure (ODS) level: ODS-2 and its successor ODS-5. The initial port of Perl to VMS pre-dates ODS-5, but all current testing and development assumes ODS-5 and its capabilities, including case preservation, extended characters in filespecs, and names up to 8192 bytes long.
Perl on VMS can accept either VMS- or Unix-style file specifications as in either of the following:
$ perl -ne "print if /perl_setup/i" SYS$LOGIN:LOGIN.COM
$ perl -ne "print if /perl_setup/i" /sys$login/login.com
but not a mixture of both as in:
$ perl -ne "print if /perl_setup/i" sys$login:/login.com
Can't open sys$login:/login.com: file specification syntax error
In general, the easiest path to portability is always to specify
filenames in Unix format unless they will need to be processed by native
commands or utilities. Because of this latter consideration, the
the File::Spec manpage module by default returns native format specifications
regardless of input format. This default may be reversed so that
filenames are always reported in Unix format by specifying the
DECC$FILENAME_UNIX_REPORT feature logical in the environment.
The file type, or extension, is always present in a VMS-format file
specification even if it's zero-length. This means that, by default,
readdir will return a trailing dot on a
file with no extension, so where you would see "a" on Unix you'll see
"a." on VMS. However, the trailing dot may be suppressed by enabling
the DECC$READDIR_DROPDOTNOTYPE feature in the environment (see the CRTL
documentation on feature logical names).
What \n represents depends on the type of file opened. It usually
represents \012 but it could also be \015, \012, \015\012,
\000, \040, or nothing depending on the file organization and
record format. The VMS::Stdio module provides access to
the special fopen() requirements of files with unusual attributes on
VMS.
The value of $^O on OpenVMS is ``VMS''. To determine the
architecture that you are running on refer to
$Config{archname}>|Config/archname.
On VMS, perl determines the UTC offset from the SYS$TIMEZONE_DIFFERENTIAL
logical name. Although the VMS epoch began at 17-NOV-1858 00:00:00.00,
calls to localtime are adjusted to count
offsets from 01-JAN-1970 00:00:00.00, just like Unix.
Also see:
Perl on VOS (also known as OpenVOS) is discussed in README.vos in the Perl distribution (installed as perlvos). Perl on VOS can accept either VOS- or Unix-style file specifications as in either of the following:
$ perl -ne "print if /perl_setup/i" >system>notices
$ perl -ne "print if /perl_setup/i" /system/notices
or even a mixture of both as in:
$ perl -ne "print if /perl_setup/i" >system/notices
Even though VOS allows the slash character to appear in object names, because the VOS port of Perl interprets it as a pathname delimiting character, VOS files, directories, or links whose names contain a slash character cannot be processed. Such files must be renamed before they can be processed by Perl.
Older releases of VOS (prior to OpenVOS Release 17.0) limit file
names to 32 or fewer characters, prohibit file names from
starting with a - character, and prohibit file names from
containing (space) or any character from the set !#%&'()*;<=>?.
Newer releases of VOS (OpenVOS Release 17.0 or later) support a
feature known as extended names. On these releases, file names
can contain up to 255 characters, are prohibited from starting
with a - character, and the set of prohibited characters is
reduced to #%*<>?. There are
restrictions involving spaces and apostrophes: these characters
must not begin or end a name, nor can they immediately precede or
follow a period. Additionally, a space must not immediately
precede another space or hyphen. Specifically, the following
character combinations are prohibited: space-space,
space-hyphen, period-space, space-period, period-apostrophe,
apostrophe-period, leading or trailing space, and leading or
trailing apostrophe. Although an extended file name is limited
to 255 characters, a path name is still limited to 256
characters.
The value of $^O on VOS is ``vos''. To determine the
architecture that you are running on refer to
$Config{archname}>|Config/archname.
Also see:
There is no specific mailing list for Perl on VOS. You can contact the Stratus Technologies Customer Assistance Center (CAC) for your region, or you can use the contact information located in the distribution files on the Stratus Anonymous FTP site.
Stratus Technologies on the web at http://www.stratus.com VOS Open-Source Software on the web at http://ftp.stratus.com/pub/vos/vos.html
v5.22 core Perl runs on z/OS (formerly OS/390). Theoretically it could run on the successors of OS/400 on AS/400 minicomputers as well as VM/ESA, and BS2000 for S/390 Mainframes. Such computers use EBCDIC character sets internally (usually Character Code Set ID 0037 for OS/400 and either 1047 or POSIX-BC for S/390 systems).
The rest of this section may need updating, but we don't know what it should say. Please email comments to perlbug@perl.org.
On the mainframe Perl currently works under the ``Unix system services for OS/390'' (formerly known as OpenEdition), VM/ESA OpenEdition, or the BS200 POSIX-BC system (BS2000 is supported in Perl 5.6 and greater). See perlos390 for details. Note that for OS/400 there is also a port of Perl 5.8.1/5.10.0 or later to the PASE which is ASCII-based (as opposed to ILE which is EBCDIC-based), see perlos400.
As of R2.5 of USS for OS/390 and Version 2.3 of VM/ESA these Unix
sub-systems do not support the #! shebang trick for script invocation.
Hence, on OS/390 and VM/ESA Perl scripts can be executed with a header
similar to the following simple script:
: # use perl
eval 'exec /usr/local/bin/perl -S $0 ${1+"$@"}'
if 0;
#!/usr/local/bin/perl # just a comment really
print "Hello from perl!\n";
OS/390 will support the #! shebang trick in release 2.8 and beyond.
Calls to system and backticks can use POSIX
shell syntax on all S/390 systems.
On the AS/400, if PERL5 is in your library list, you may need to wrap your Perl scripts in a CL procedure to invoke them like so:
BEGIN
CALL PGM(PERL5/PERL) PARM('/QOpenSys/hello.pl')
ENDPGM
This will invoke the Perl script hello.pl in the root of the
QOpenSys file system. On the AS/400 calls to
system or backticks must use CL syntax.
On these platforms, bear in mind that the EBCDIC character set may have
an effect on what happens with some Perl functions (such as
chr, pack,
print,
printf,
ord, sort,
sprintf,
unpack), as
well as bit-fiddling with ASCII constants using operators like
^, & and , not to mention
dealing with socket interfaces to ASCII computers (see Newlines).
Fortunately, most web servers for the mainframe will correctly
translate the \n in the following statement to its ASCII equivalent
(\r is the same under both Unix and z/OS):
print "Content-type: text/html\r\n\r\n";
The values of $^O on some of these platforms include:
uname $^O $Config{archname}
--------------------------------------------
OS/390 os390 os390
OS400 os400 os400
POSIX-BC posix-bc BS2000-posix-bc
Some simple tricks for determining if you are running on an EBCDIC platform could include any of the following (perhaps all):
if ("\t" eq "\005") { print "EBCDIC may be spoken here!\n"; }
if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; }
if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; }
One thing you may not want to rely on is the EBCDIC encoding of punctuation characters since these may differ from code page to code page (and once your module or script is rumoured to work with EBCDIC, folks will want it to work with all EBCDIC character sets).
Also see:
Because Acorns use ASCII with newlines (\n) in text files as \012 like
Unix, and because Unix filename emulation is turned on by default,
most simple scripts will probably work ``out of the box''. The native
filesystem is modular, and individual filesystems are free to be
case-sensitive or insensitive, and are usually case-preserving. Some
native filesystems have name length limits, which file and directory
names are silently truncated to fit. Scripts should be aware that the
standard filesystem currently has a name length limit of 10
characters, with up to 77 items in a directory, but other filesystems
may not impose such limitations.
Native filenames are of the form
Filesystem#Special_Field::DiskName.$.Directory.Directory.File
where
Special_Field is not usually present, but may contain . and $ .
Filesystem =~ m|[A-Za-z0-9_]|
DsicName =~ m|[A-Za-z0-9_/]|
$ represents the root directory
. is the path separator
@ is the current directory (per filesystem but machine global)
^ is the parent directory
Directory and File =~ m|[^\0- "\.\$\%\&:\@\\^\|\177]+|
The default filename translation is roughly tr|/.|./|, swapping dots
and slashes.
Note that "ADFS::HardDisk.$.File" ne 'ADFS::HardDisk.$.File' and that
the second stage of $ interpolation in regular expressions will fall
foul of the $. variable if scripts are not careful.
Logical paths specified by system variables containing comma-separated
search lists are also allowed; hence System:Modules is a valid
filename, and the filesystem will prefix Modules with each section of
System$Path until a name is made that points to an object on disk.
Writing to a new file System:Modules would be allowed only if
System$Path contains a single item list. The filesystem will also
expand system variables in filenames if enclosed in angle brackets, so
<System$Dir>.Modules would look for the file
$ENV{'System$Dir'} . 'Modules'. The obvious implication of this is
that fully qualified filenames can start with <> and the
three-argument form of open should
always be used.
Because . was in use as a directory separator and filenames could not
be assumed to be unique after 10 characters, Acorn implemented the C
compiler to strip the trailing .c .h .s and .o suffix from
filenames specified in source code and store the respective files in
subdirectories named after the suffix. Hence files are translated:
foo.h h.foo
C:foo.h C:h.foo (logical path variable)
sys/os.h sys.h.os (C compiler groks Unix-speak)
10charname.c c.10charname
10charname.o o.10charname
11charname_.c c.11charname (assuming filesystem truncates at 10)
The Unix emulation library's translation of filenames to native assumes
that this sort of translation is required, and it allows a user-defined list
of known suffixes that it will transpose in this fashion. This may
seem transparent, but consider that with these rules foo/bar/baz.h
and foo/bar/h/baz both map to foo.bar.h.baz, and that
readdir and glob
cannot and do not attempt to emulate the reverse mapping. Other
.'s in filenames are translated to /.
As implied above, the environment accessed through
%ENV is global, and the convention is that program
specific environment variables are of the form Program$Name.
Each filesystem maintains a current directory,
and the current filesystem's current directory is the global current
directory. Consequently, sociable programs don't change the current
directory but rely on full pathnames, and programs (and Makefiles) cannot
assume that they can spawn a child process which can change the current
directory without affecting its parent (and everyone else for that
matter).
Because native operating system filehandles are global and are currently
allocated down from 255, with 0 being a reserved value, the Unix emulation
library emulates Unix filehandles. Consequently, you can't rely on
passing STDIN, STDOUT, or STDERR to your children.
The desire of users to express filenames of the form
<Foo$Dir>.Bar on the command line unquoted causes problems,
too: ``>|perlop/qx/STRING/ 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, QNX, Plan 9, and VOS, have been well-integrated into the standard Perl source code kit. You may need to see the ports/ directory on CPAN for information, and possibly binaries, for the likes of: aos, Atari ST, lynxos, riscos, Novell Netware, Tandem Guardian, etc. (Yes, we know that some of these OSes may fall under the Unix category, but we are not a standards body.)
Some approximate operating system names and their $^O
values in the ``OTHER'' category include:
OS $^O $Config{archname}
------------------------------------------
Amiga DOS amigaos m68k-amigos
See also:
Listed below are functions that are either completely unimplemented or else have been implemented differently on various platforms. Preceding each description will be, in parentheses, a list of platforms that the description applies to.
The list may well be incomplete, or even wrong in some places. When in doubt, consult the platform-specific README files in the Perl source distribution, and any other documentation resources accompanying a given port.
Be aware, moreover, that even among Unix-ish systems there are variations.
For many functions, you can also query %Config,
exported by default from the Config module. For example, to
check whether the platform has the lstat
call, check $Config{d_lstat}>|Config/d_lstat. See the Config manpage for a
full description of available variables.
-w only inspects the read-only file attribute (FILE_ATTRIBUTE_READONLY),
which determines whether the directory can be deleted, not whether it can
be written to. Directories always have read and write access unless denied
by discretionary access control lists (DACLs).
(VMS)
-r, -w, -x, and -o tell whether the file is accessible,
which may not reflect UIC-based file protections.
(RISC OS)
-s by name on an open file will return the space reserved on disk,
rather than the current extent. -s on an open filehandle returns the
current size.
(Win32, VMS, RISC OS)
-R, -W, -X, -O are indistinguishable from -r, -w,
-x, -o.
(Win32, VMS, RISC OS)
-g, -k, -l, -u, -A are not particularly meaningful.
(VMS, RISC OS)
-p is not particularly meaningful.
(VMS)
-d is true if passed a device spec without an explicit directory.
(Win32)
-x (or -X) determine if a file ends in one of the executable
suffixes. -S is meaningless.
(RISC OS)
-x (or -X) determine if a file has an executable file type.
atan2 may vary depending on any combination of the above.
Perl attempts to conform to the Open Group/IEEE standards for the results
returned from atan2, but cannot force the issue if the system Perl is
run on does not allow it.
The current version of the standards for atan2 is available at
http://www.opengroup.org/onlinepubs/009695399/functions/atan2.html.
(VMS) Reopens file and restores pointer; if function fails, underlying filehandle may be closed, or pointer may be in a different position.
(Win32)
The value returned by tell may be affected
after the call, and the filehandle may be flushed.
(RISC OS) Only good for changing ``owner'' and ``other'' read-write access.
(VOS) Access permissions are mapped onto VOS access-control list changes.
(Cygwin)
The actual permissions set depend on the value of the CYGWIN variable
in the SYSTEM environment settings.
(Android) Setting the exec bit on some locations (generally /sdcard) will return true but not actually set the bit.
(VMS) A mode argument of zero sets permissions to the user's default permission mask rather than disabling all permissions.
(Win32) Does nothing, but won't fail.
(VOS) A little funky, because VOS's notion of ownership is a little funky.
(Android) Not implemented.
(Cygwin, Win32) Not supported.
(VMS) Invokes VMS debugger.
exec LIST without the use of indirect object syntax (exec PROGRAM LIST)
may fall back to trying the shell if the first spawn() fails.
Note that the list form of exec() is emulated since the Win32 API
CreateProcess() accepts a simple string rather than an array of
command-line arguments. This may have security implications for your
code.
(SunOS, Solaris, HP-UX) Does not automatically flush output handles on some platforms.
(Symbian OS) Not supported.
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'>|vmsish/vmsish exit. As with
the CRTL's exit() function, exit 0 is also mapped to an exit status
of SS$_NORMAL (1); this mapping cannot be overridden. Any other
argument to exit
is used directly as Perl's exit status. On VMS, unless the future
POSIX_EXIT mode is enabled, the exit code should always be a valid
VMS exit code and not a generic number. When the POSIX_EXIT mode is
enabled, a generic number will be encoded in a method compatible with
the C library _POSIX_EXIT macro so that it can be decoded by other
programs, particularly ones written in C, like the GNV package.
(Solaris)
exit resets file pointers, which is a problem when called
from a child process (created by fork) in
BEGIN.
A workaround is to use POSIX::_exit>|POSIX/_exit.
exit unless $Config{archname} =~ /\bsolaris\b/;
require POSIX;
POSIX::_exit(0);
(VMS) Some functions available based on the version of VMS.
(Win32) Emulated using multiple interpreters. See the perlfork manpage.
(SunOS, Solaris, HP-UX) Does not automatically flush output handles on some platforms.
(RISC OS) Not useful.
(RISC OS) Not useful.
gethostbyname('localhost') does not work everywhere: you may have
to use gethostbyname('127.0.0.1').
(Android) Either not implemented or a no-op.
File::Glob extension
on most platforms. See the File::Glob manpage for portability information.
gmtime is reliable from -2**63 to 2**63-1. However,
because work-arounds in the implementation use floating point numbers,
it will become inaccurate as the time gets larger. This is a bug and
will be fixed in the future.
(VOS) Time values are 32-bit quantities.
(Win32)
Available only for socket handles, and it does what the ioctlsocket() call
in the Winsock API does.
(RISC OS) Available only for socket handles.
(Win32)
kill doesn't send a signal to the identified process like it does on
Unix platforms. Instead kill($sig, $pid) terminates the process
identified by $pid, and makes it exit immediately with exit status
$sig. As in Unix, if $sig is 0 and the specified process exists, it
returns true without actually terminating it.
(Win32)
kill(-9, $pid) will terminate the process specified by $pid and
recursively all child processes owned by it. This is different from
the Unix semantics, where the signal will be delivered to all
processes in the same process group as the process specified by
$pid.
(VMS) A pid of -1 indicating all processes on the system is not currently supported.
(AmigaOS) Link count not updated because hard links are not quite that hard (They are sort of half-way between hard and soft links).
(Win32) Hard links are implemented on Win32 under NTFS only. They are natively supported on Windows 2000 and later. On Windows NT they are implemented using the Windows POSIX subsystem support and the Perl process will need Administrator or Backup Operator privileges to create hard links.
(VMS) Available on 64 bit OpenVMS 8.2 and later.
localtime has the same range as gmtime, but because time zone
rules change, its accuracy for historical and future times may degrade
but usually by no more than an hour.
(Win32) Return values (especially for device and inode) may be bogus.
|- and -| are unsupported.
(SunOS, Solaris, HP-UX) Opening a process does not automatically flush output handles on some platforms.
(Win32)
Both of modes |- and -| are supported, but the list form is
emulated since the Win32 API CreateProcess() accepts a simple string
rather than an array of arguments. This may have security
implications for your code.
readdir to re-read the
directory stream. The entries already read before the rewinddir call
will just be returned again from a cache buffer.
(RISC OS) Only reliable on sockets.
Note that the select FILEHANDLE form is
generally portable.
alarm, and limited to a
maximum of 4294967 seconds, approximately 49 days.
(VMS) Available on 64 bit OpenVMS 8.2 and later.
rdev, blksize, or blocks will return
these as '', so numeric comparison or manipulation of these fields may
cause 'not numeric' warnings.
(Mac OS X)
ctime not supported on UFS.
(Win32)
ctime is creation time instead of inode change time.
(Win32)
dev and ino are not meaningful.
(VMS)
dev and ino are not necessarily reliable.
(RISC OS)
mtime, atime and ctime all return the last modification time.
dev and ino are not necessarily reliable.
(OS/2)
dev, rdev, blksize, and blocks are not available. ino is not
meaningful and will differ between stat calls on the same file.
(Cygwin)
Some versions of cygwin when doing a stat("foo") and not finding it
may then attempt to stat("foo.exe").
(Win32)
stat needs to open the file to determine the link count
and update attributes that may have been changed through hard links.
Setting ${^WIN32_SLOPPY_STAT} to a
true value speeds up stat by not performing this operation.
(VMS) Implemented on 64 bit VMS 8.3. VMS requires the symbolic link to be in Unix syntax if it is intended to resolve to a valid path.
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.
$ENV{PERL5SHELL}. system(1, @args) spawns an external
process and immediately returns its process designator, without
waiting for it to terminate. Return value may be used subsequently
in wait or waitpid.
Failure to spawn() a subprocess is indicated by setting
$? to 255 << 8. $? is set in a
way compatible with Unix (i.e. the exit status of the subprocess is
obtained by $? >> 8, as described in the documentation).
Note that the list form of system() is emulated since the Win32 API
CreateProcess() accepts a simple string rather than an array of
command-line arguments. This may have security implications for your
code.
(RISC OS)
There is no shell to process metacharacters, and the native standard is
to pass a command line terminated by ``\n'' ``\r'' or ``\0'' to the spawned
program. Redirection such as > foo is performed (if at all) by
the run time library of the spawned program. system LIST will call
the Unix emulation library's exec emulation,
which attempts to provide emulation of the stdin, stdout, stderr in force
in the parent, provided the child program uses a compatible version of the
emulation library. system SCALAR will call the native command line
directly and no such emulation of a child Unix program will occur.
Mileage will vary.
(Win32)
system LIST without the use of indirect object syntax (system PROGRAM LIST)
may fall back to trying the shell if the first spawn() fails.
(SunOS, Solaris, HP-UX) Does not automatically flush output handles on some platforms.
(VMS)
As with Win32, system(1, @args) spawns an external process and
immediately returns its process designator without waiting for the
process to terminate. In this case the return value may be used subsequently
in wait or waitpid.
Otherwise the return value is POSIX-like (shifted up by 8 bits), which only
allows room for a made-up value derived from the severity bits of the native
32-bit condition code (unless overridden by
use vmsish 'status'>|vmsish/vmsish status). If the native
condition code is one that has a POSIX value encoded, the POSIX value will
be decoded to extract the expected exit value. For more details see
$? in the perlvms manpage.
clock() function in the C
runtime library.
(RISC OS) Not useful.
(VOS) Truncation to same-or-shorter lengths only.
(Win32)
If a FILEHANDLE is supplied, it must be writable and opened in append
mode (i.e., use open(my $fh, '>>', 'filename')
or sysopen(my $fh, ..., O_APPEND|O_RDWR). If a filename is supplied, it
should not be held open elsewhere.
undef where unavailable.
(AmigaOS)
umask works but the correct permissions are set only when the file
is finally closed.
(Win32)
May not behave as expected. Behavior depends on the C runtime
library's implementation of utime(), and the filesystem
being used. The FAT filesystem typically does not support an ``access
time'' field, and it may limit timestamps to a granularity of two seconds.
system(1, ...) or pseudo processes created with
fork.
(RISC OS) Not useful.
The following platforms are known to build Perl 5.12 (as of April 2010, its release date) from the standard source code distribution available at http://www.cpan.org/src
The FreeMiNT port uses GNU dld for loadable module capabilities. So ensure you have that library installed when building perl.
The following platforms were supported by a previous version of Perl but have been officially removed from Perl's source code as of 5.20:
The following platforms were supported up to 5.10. They may still have worked in 5.12, but supporting code has been removed for 5.14:
The following platforms were supported by a previous version of Perl but have been officially removed from Perl's source code as of 5.12:
As of July 2002 (the Perl release 5.8.0), the following platforms were able to build Perl from the standard source code distribution available at http://www.cpan.org/src/
AIX
BeOS
BSD/OS (BSDi)
Cygwin
DG/UX
DOS DJGPP 1)
DYNIX/ptx
EPOC R5
FreeBSD
HI-UXMPP (Hitachi) (5.8.0 worked but we didn't know it)
HP-UX
IRIX
Linux
Mac OS Classic
Mac OS X (Darwin)
MPE/iX
NetBSD
NetWare
NonStop-UX
ReliantUNIX (formerly SINIX)
OpenBSD
OpenVMS (formerly VMS)
Open UNIX (Unixware) (since Perl 5.8.1/5.9.0)
OS/2
OS/400 (using the PASE) (since Perl 5.8.1/5.9.0)
POSIX-BC (formerly BS2000)
QNX
Solaris
SunOS 4
SUPER-UX (NEC)
Tru64 UNIX (formerly DEC OSF/1, Digital UNIX)
UNICOS
UNICOS/mk
UTS
VOS / OpenVOS
Win95/98/ME/2K/XP 2)
WinCE
z/OS (formerly OS/390)
VM/ESA
1) in DOS mode either the DOS or OS/2 ports can be used
2) compilers: Borland, MinGW (GCC), VC6
The following platforms worked with the previous releases (5.6 and 5.7), but we did not manage either to fix or to test these in time for the 5.8.0 release. There is a very good chance that many of these will work fine with the 5.8.0.
BSD/OS
DomainOS
Hurd
LynxOS
MachTen
PowerMAX
SCO SV
SVR4
Unixware
Windows 3.1
Known to be broken for 5.8.0 (but 5.6.1 and 5.7.2 can be used):
AmigaOS 3
The following platforms have been known to build Perl from source in the past (5.005_03 and earlier), but we haven't been able to verify their status for the current release, either because the hardware/software platforms are rare or because we don't have an active champion on these platforms--or both. They used to work, though, so go ahead and try compiling them, and let 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
MPC
NEWS-OS
NextSTEP
OpenSTEP
Opus
Plan 9
RISC/os
SCO ODT/OSR
Stellar
SVR2
TI1500
TitanOS
Ultrix
Unisys Dynix
The following platforms have their own source code distributions and binaries available via http://www.cpan.org/ports/
Perl release
OS/400 (ILE) 5.005_02
Tandem Guardian 5.004
The following platforms have only binaries available via http://www.cpan.org/ports/index.html :
Perl release
Acorn RISCOS 5.005_02
AOS 5.002
LynxOS 5.004_02
Although we do suggest that you always build your own Perl from the source code, both for maximal configurability and for security, in case you are in a hurry you can check http://www.cpan.org/ports/index.html for binary distributions.
perlaix, perlamiga, perlbs2000, perlce, perlcygwin, perldos, the perlebcdic manpage, perlfreebsd, perlhurd, perlhpux, perlirix, perlmacos, perlmacosx, perlnetware, perlos2, perlos390, perlos400, perlplan9, perlqnx, perlsolaris, perltru64, the perlunicode manpage, the perlvms manpage, perlvos, perlwin32, and the Win32 manpage.
Abigail <abigail@abigail.be>, Charles Bailey <bailey@newman.upenn.edu>, Graham Barr <gbarr@pobox.com>, Tom Christiansen <tchrist@perl.com>, Nicholas Clark <nick@ccl4.org>, Thomas Dorner <Thomas.Dorner@start.de>, Andy Dougherty <doughera@lafayette.edu>, Dominic Dunlop <domo@computer.org>, Neale Ferguson <neale@vma.tabnsw.com.au>, David J. Fiander <davidf@mks.com>, Paul Green <Paul.Green@stratus.com>, M.J.T. Guy <mjtg@cam.ac.uk>, Jarkko Hietaniemi <jhi@iki.fi>, Luther Huffman <lutherh@stratcom.com>, Nick Ing-Simmons <nick@ing-simmons.net>, Andreas J. König <a.koenig@mind.de>, Markus Laker <mlaker@contax.co.uk>, Andrew M. Langmead <aml@world.std.com>, Lukas Mai <l.mai@web.de>, Larry Moore <ljmoore@freespace.net>, Paul Moore <Paul.Moore@uk.origin-it.com>, Chris Nandor <pudge@pobox.com>, Matthias Neeracher <neeracher@mac.com>, Philip Newton <pne@cpan.org>, Gary Ng <71564.1743@CompuServe.COM>, Tom Phoenix <rootbeer@teleport.com>, André Pirard <A.Pirard@ulg.ac.be>, Peter Prymmer <pvhp@forte.com>, Hugo van der Sanden <hv@crypt0.demon.co.uk>, Gurusamy Sarathy <gsar@activestate.com>, Paul J. Schinder <schinder@pobox.com>, Michael G Schwern <schwern@pobox.com>, Dan Sugalski <dan@sidhe.org>, Nathan Torkington <gnat@frii.com>, John Malmberg <wb8tyw@qsl.net>
| perlport - Writing portable Perl |