From Linux Man Pages
perlport - Writing portable Perl
DESCRIPTION
Perl runs on numerous operating systems. While most of them share much in common, they also have their own
unique features.
This document is meant to help you to find out what constitutes portable Perl code. That way once you make a
decision to write portably, you know where the lines are drawn, and you can stay within them.
There is a tradeoff between taking full advantage of one particular type of computer and taking advantage of a
full range of them. Naturally, as you broaden your range and become more diverse, the common factors drop, and
you are left with an increasingly smaller area of common ground in which you can operate to accomplish a particu-
lar 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 cod-
ing have the full generality of being portable, or whether to just get the job done right now. This is the hard-
est choice to be made. The rest is easy, because Perl provides many choices, whichever way you want to approach
your problem.
Looking at it another way, writing portable code is usually about willfully limiting your available choices.
Naturally, it takes discipline and sacrifice to do that. The product of portability and convenience may be a
constant. You have been warned.
Be aware of two important points:
Not all Perl programs have to be portable
There is no reason you should not use Perl as a language to glue Unix tools together, or to prototype a Mac-
intosh application, or to manage the Windows registry. If it makes no sense to aim for portability for one
reason or another in a given program, then don't bother.
Nearly all of Perl already is portable
Don't be fooled into thinking that it is hard to create portable Perl code. It isn't. Perl tries its level-
best to bridge the gaps between what's available on different platforms, and all the means available to use
those features. Thus almost all Perl code runs on any machine without modification. But there are some sig-
nificant 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 pro-
gramming (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-spe-
cific 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 idiosyn-
crasies of some of the ports, almost all of which are in a state of constant evolution. Thus, this material
should be considered a perpetual work in progress ("<IMG SRC="yellow_sign.gif" ALT="Under Construction">").
ISSUES
Newlines
In most operating systems, lines in files are terminated by newlines. Just what is used as a newline may vary
from OS to OS. Unix traditionally uses "\012", one type of DOSish I/O uses "\015\012", and Mac OS uses "\015".
Perl uses "\n" to represent the "logical" newline, where what is logical may depend on the platform in use. In
MacPerl, "\n" always means "\015". In DOSish perls, "\n" usually means "\012", but when accessing a file in
"text" mode, STDIO translates it to (or from) "\015\012", depending on whether you're reading or writing. Unix
does the same thing on ttys in canonical mode. "\015\012" is 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 Dunce::Files module can help audit your code for misuses of chop().
When dealing with binary files (or text files in binary mode) be sure to explicitly set $/ to the appropriate
value for your file format before using chomp().
Because of the "text" mode translation, DOSish perls have limitations in using "seek" and "tell" on a file
accessed in "text" mode. Stick to "seek"-ing to locations you got from "tell" (and no others), and you are usu-
ally free to use "seek" and "tell" even in "text" mode. Using "seek" or "tell" or other file operations may be
non-portable. If you use "binmode" on a file, however, you can usually "seek" and "tell" with arbitrary values
in safety.
A common misconception in socket programming is that "\n" eq "\012" everywhere. When using protocols such as
common Internet protocols, "\012" and "\015" are called for specifically, and the values of the logical "\n" and
"\r" (carriage return) are not reliable.
print SOCKET "Hi there, client!\r\n"; # WRONG
print SOCKET "Hi there, client!\015\012"; # RIGHT
However, using "\015\012" (or "\cM\cJ", or "\x0D\x0A") can be tedious and unsightly, as well as confusing to
those maintaining the code. As such, the Socket module supplies the Right Thing for those who want it.
use Socket qw(:DEFAULT :crlf);
print SOCKET "Hi there, client!$CRLF" # RIGHT
When reading from a socket, remember that the default input record separator $/ is "\n", but robust socket code
will recognize as either "\012" or "\015\012" as end of line:
while (<SOCKET>) {
# ...
}
Because both CRLF and LF end in LF, the input record separator can be set to LF and any CR stripped later. Bet-
ter to write:
use Socket qw(:DEFAULT :crlf);
local($/) = 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 trans-
late 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 mate-
rial is similar to "Unix" but the code numbers change:
LF eq \025 eq \x15 eq \cU eq chr(21) eq CP-1047 21
LF eq \045 eq \x25 eq chr(37) eq CP-0037 37
CR eq \015 eq \x0D eq \cM eq chr(13) eq CP-1047 13
CR eq \015 eq \x0D eq \cM eq chr(13) eq CP-0037 13
| z/OS | OS/400 |
----------------------
\n | LF | LF |
\r | CR | CR |
\n * | LF | LF |
\r * | CR | CR |
----------------------
* text-mode STDIO
Numbers endianness and Width
Different CPUs store integers and floating point numbers in different orders (called endianness) and widths
(32-bit and 64-bit being the most common today). This affects your programs when they attempt to transfer num-
bers 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 mat-
ters.
The v-strings are portable only up to v2147483647 (0x7FFFFFFF), that's how far EBCDIC, or more precisely UTF-
EBCDIC will go.
Files and Filesystems
Most platforms these days structure files in a hierarchical fashion. So, it is reasonably safe to assume that
all platforms support the notion of a "path" to uniquely identify a file on the system. How that path is really
written, though, differs considerably.
Although similar, file path specifications differ between Unix, Windows, Mac OS, OS/2, VMS, VOS, RISC OS, and
probably others. Unix, for example, is one of the few OSes that has the elegant idea of a single root directory.
DOS, OS/2, VMS, VOS, and Windows can work similarly to Unix with "/" as path separator, or in their own idiosyn-
cratic 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 some-
times 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 con-
figuration 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 separa-
tor 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 charac-
ters (except for ".") in the names, and keep them to the 8.3 convention, for maximum portability, onerous a bur-
den though this may appear.
Likewise, when using the AutoSplit module, try to keep your functions to 8.3 naming and case-insensitive conven-
tions; 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 toler-
ated, 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 read-
ing, 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 path-
name, and so on). For the same reasons, avoid "@", ";" and "|".
Don't assume that in pathnames you can collapse two leading slashes "//" into one: some networking and clustering
filesystems have special semantics for that. Let the operating system to sort it out.
The portable filename characters as defined by ANSI C are
a b c d e f g h i j k l m n o p q r t u v w x y z
A B C D E F G H I J K L M N O P Q R T U V W X Y Z
0 1 2 3 4 5 6 7 8 9
. _ -
and the "-" shouldn't be the first character. If you want to be hypercorrect, stay case-insensitive and within
the 8.3 naming convention (all the files and directories have to be unique within one directory if their names
are lowercased and truncated to eight characters before the ".", if any, and to three characters after the ".",
if any). (And do not use "."s in directory names.)
System Interaction
Not all platforms provide a command line. These are usually platforms that rely primarily on a Graphical User
Interface (GUI) for user interaction. A program requiring a command line interface might not work everywhere.
This is probably for the user of the program to deal with, so don't stay up late worrying about it.
Some platforms can't delete or rename files held open by the system, this limitation may also apply to changing
filesystem metainformation like file permissions or owners. Remember to "close" files when you are done with
them. Don't "unlink" or "rename" an open file. Don't "tie" or "open" a file already tied or opened; "untie" or
"close" it first.
Don't open the same file more than once at a time for writing, as some operating systems put 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 ver-
sions 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-sensi-
tive, 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 ta-
ble.
Don't count on signals or %SIG for anything.
Don't count on filename globbing. Use "opendir", "readdir", and "closedir" instead.
Don't count on per-program environment variables, or per-program current directories.
Don't count on specific values of $!, neither numeric nor especially the strings values-- users may switch their
locales causing error messages to be translated into their languages. If you can trust a POSIXish environment,
you can portably use the symbols defined by the Errno module, like ENOENT. And don't trust on the values of $!
at all except immediately after a failed system call.
Command names versus file pathnames
Don't assume that the name used to invoke a command or program with "system" or "exec" can also be used to test
for the existence of the file that holds the executable code for that command or program. First, many systems
have "internal" commands that are built-in to the shell or OS and while these commands can be invoked, there is
no corresponding file. Second, some operating systems (e.g., Cygwin, DJGPP, OS/2, and VOS) have required suf-
fixes 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 oper-
ating 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 num-
ber in the VMS file name.
To convert $^X to a file pathname, taking account of the requirements of the various operating system possibili-
ties, say:
use Config;
$thisperl = $^X;
if ($^O ne 'VMS')
{$thisperl .= $Config{_exe} unless $thisperl =~ m/$Config{_exe}$/i;}
To convert $Config{perlpath} to a file pathname, say:
use Config;
$thisperl = $Config{perlpath};
if ($^O ne 'VMS')
{$thisperl .= $Config{_exe} unless $thisperl =~ m/$Config{_exe}$/i;}
Networking
Don't assume that you can reach the public Internet.
Don't assume that there is only one way to get through firewalls to the public Internet.
Don't assume that you can reach outside world through any other port than 80, or some web proxy. ftp is blocked
by many firewalls.
Don't assume that you can send email by connecting to the local SMTP port.
Don't assume that you can reach yourself or any node by the name 'localhost'. The same goes for '127.0.0.1'.
You will have to try both.
Don't assume that the host has only one network card, or that it can't bind to many virtual IP addresses.
Don't assume a particular network device name.
Don't assume a particular set of ioctl()s will work.
Don't assume that you can ping hosts and get replies.
Don't assume that any particular port (service) will respond.
Don't assume that Sys::Hostname (or any other API or command) returns either a fully qualified 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.
Interprocess Communication (IPC)
In general, don't directly access the system in code meant to be portable. That means, no "system", "exec",
"fork", "pipe", ``, "qx//", "open" with a "|", nor any of the other things that makes being a perl hacker worth
being.
Commands that launch external processes are generally supported on most platforms (though many of them do not
support any type of forking). The problem with using them arises from what you invoke them on. External tools
are often named differently on different platforms, may not be available in the same location, might accept dif-
ferent 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 proba-
bly 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 distribu-
tion 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 sim-
ple, 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 imple-
ment it with platform-specific code, but expose a common interface).
External Subroutines (XS)
XS code can usually be made to work with any platform, but dependent libraries, header files, etc., might not be
readily available or portable, or the XS code itself might be platform-specific, just as Perl code might be. If
the libraries and headers are portable, then it is normally reasonable to make sure the XS code is portable, too.
A different type of portability issue arises when writing XS code: availability of a C compiler on the end-user's
system. C brings with it its own portability issues, and writing XS code will expose you to some of those.
Writing purely in Perl is an easier way to achieve portability.
Standard Modules
In general, the standard modules work across platforms. Notable exceptions are the CPAN module (which currently
makes connections to external programs that may not be available), platform-specific modules (like ExtU-
tils::MM_VMS), and DBM modules.
There is no one DBM module available on all platforms. SDBM_File and the others are generally available on all
Unix and DOSish ports, but not in MacPerl, where only NBDM_File and DB_File are available.
The good news is that at least some DBM module should be available, and AnyDBM_File will use whichever module it
can find. Of course, then the code needs to be fairly strict, dropping to the greatest common factor (e.g., not
exceeding 1K for each record), so that it will work with any DBM module. See AnyDBM_File for more details.
Time and Date
The system's notion of time of day and calendar date is controlled in widely different ways. Don't assume the
timezone is stored in $ENV{TZ}, and even if it is, don't assume that you can control the timezone through that
variable. Don't assume anything about the three-letter timezone abbreviations (for example that MST would be the
Mountain Standard Time, it's been known to stand for Moscow Standard Time). If you need to use timezones,
express them in some unambiguous format like the exact number of minutes offset from UTC, or the POSIX timezone
format.
Don't assume that the epoch starts at 00:00:00, January 1, 1970, because that is OS- and implementation-specific.
It is better to store a date in an unambiguous representation. The ISO 8601 standard defines YYYY-MM-DD as the
date format, or YYYY-MM-DDTHH-MM-SS (that's a literal "T" separating the date from the time). Please do use the
ISO 8601 instead of making us to guess what date 02/03/04 might be. ISO 8601 even sorts nicely as-is. A text
representation (like "1987-12-18") can be easily converted into an OS-specific value using a module like
Date::Parse. An array of values, such as those returned by "localtime", can be converted to an OS-specific rep-
resentation using Time::Local.
When calculating specific times, such as for tests in time or date modules, it may be appropriate to calculate an
offset for the epoch.
require Time::Local;
$offset = Time::Local::timegm(0, 0, 0, 1, 0, 70);
The value for $offset in Unix will be 0, but in Mac OS will be some large number. $offset can then be added to a
Unix time value to get what should be the proper value on any system.
On Windows (at least), you shouldn't pass a negative value to "gmtime" or "localtime".
Character sets and character encoding
Assume very little about character sets.
Assume nothing about numerical values ("ord", "chr") of characters. Do not use explicit code point ranges (like
\xHH-\xHH); use for example symbolic character classes like "[:print:]".
Do not assume that the alphabetic characters are encoded contiguously (in the numeric sense). There may be gaps.
Do not assume anything about the ordering of the characters. The lowercase letters may come before or after the
uppercase letters; the lowercase and uppercase may be interlaced so that both "a" and "A" come before "b"; the
accented and other international characters may be interlaced so that ae comes before "b".
Internationalisation
If you may assume POSIX (a rather large assumption), you may read more about the POSIX locale system from perllo-
cale. The locale system at least attempts to make things a little bit more portable, or at least more convenient
and native-friendly for non-English users. The system affects character sets and encoding, and date and time
formatting--amongst other things.
If you really want to be international, you should consider Unicode. See perluniintro and perlunicode for more
information.
If you want to use non-ASCII bytes (outside the bytes 0x00..0x7f) in the "source code" of your code, to be
portable you have to be explicit about what bytes they are. Someone might for example be using your code under a
UTF-8 locale, in which case random native bytes might be illegal ("Malformed UTF-8 ...") This means that for
example embedding ISO 8859-1 bytes beyond 0x7f into your strings might cause trouble later. If the bytes are
native 8-bit bytes, you can use the "bytes" pragma. If the bytes are in a string (regular expression being a
curious string), you can often also use the "\xHH" notation instead of embedding the bytes as-is. If they are in
some particular legacy encoding (ether single-byte or something more complicated), you can use the "encoding"
pragma. (If you want to write your code in UTF-8, you can use either the "utf8" pragma, or the "encoding"
pragma.) The "bytes" and "utf8" pragmata are available since Perl 5.6.0, and the "encoding" pragma since Perl
5.8.0.
System Resources
If your code is destined for systems with severely constrained (or missing!) virtual memory systems then you want
to be especially mindful of avoiding wasteful constructs such as:
# NOTE: this is no longer "bad" in perl5.005
for (0..10000000) {} # bad
for (my $x = 0; $x <= 10000000; ++$x) {} # good
@lines = <VERY_LARGE_FILE>; # bad
while (<FILE>) {$file .= $_} # sometimes bad
$file = join(, <FILE>); # better
The last two constructs may appear unintuitive to most people. The first repeatedly grows a string, whereas the
second allocates a large chunk of memory in one go. On some systems, the second is more efficient that the
first.
Security
Most multi-user platforms provide basic levels of security, usually implemented at the filesystem level. Some,
however, do not-- unfortunately. Thus the notion of user id, or "home" directory, or even the state of being
logged-in, may be unrecognizable on many platforms. If you write programs that are security-conscious, it is
usually best to know what type of system you will be running under so that you can write code explicitly for that
platform (or class of platforms).
Don't assume the UNIX filesystem access semantics: the operating system or the filesystem may be using some ACL
systems, which are richer languages than the usual rwx. Even if the rwx exist, their semantics might be differ-
ent.
(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 per-
missions check and the actual operation. Just try the operation.)
Don't assume the UNIX user and group semantics: especially, don't expect the $< and $> (or the $( and $)) to work
for switching identities (or memberships).
Don't assume set-uid and set-gid semantics. (And even if you do, think twice: set-uid and set-gid are a known can
of security worms.)
Style
For those times when it is necessary to have platform-specific code, consider keeping the platform-specific code
in one place, making porting to other platforms easier. Use the Config module and the special variable $^O to
differentiate platforms, as described in "PLATFORMS".
Be careful in the tests you supply with your module or programs. Module code may be fully portable, but its
tests might not be. This often happens when tests spawn off other processes or call external programs to aid in
the testing, or when (as noted above) the tests assume certain things about the filesystem and paths. Be careful
not to depend on a specific output style for errors, such as when checking $! after a failed system call. Using
$! for anything else than displaying it as output is doubtful (though see the Errno module for testing reasonably
portably for error value). Some platforms expect a certain output format, and Perl on those platforms may have
been adjusted accordingly. Most specifically, don't anchor a regex when testing an error value.
CPAN Testers
Modules uploaded to CPAN are tested by a variety of volunteers on different platforms. These CPAN testers are
notified by mail of each new upload, and reply to the list with PASS, FAIL, NA (not applicable to this platform),
or UNKNOWN (unknown), along with any relevant notations.
The purpose of the testing is twofold: one, to help developers fix any problems in their code that crop up
because of lack of testing on other platforms; two, to provide users with information about whether a given mod-
ule works on a given platform.
Also see:
� Mailing list: cpan-testers@perl.org
� Testing results: http://testers.cpan.org/
PLATFORMS
As of version 5.002, Perl is built with a $^O variable that indicates the operating system it was built on. This
was implemented to help speed up code that would otherwise have to "use Config" and use the value of $Con-
fig{osname}. Of course, to get more detailed information about the system, looking into %Config is certainly
recommended.
%Config cannot always be trusted, however, because it was built at compile time. If perl was built in one place,
then transferred elsewhere, some values may be wrong. The values may even have been edited after the fact.
Unix
Perl works on a bewildering variety of Unix and Unix-like platforms (see e.g. most of the files in the hints/
directory in the source code kit). On most of these systems, the value of $^O (hence $Config{'osname'}, too) is
determined either by lowercasing and stripping punctuation from the first field of the string returned by typing
"uname -a" (or a similar command) at the shell prompt or by testing the file system for the presence of uniquely
named files such as a kernel or header file. Here, for example, are a few of the more popular Unix flavors:
uname $^O $Config{'archname'}
--------------------------------------------
AIX aix aix
BSD/OS bsdos i386-bsdos
Darwin darwin darwin
dgux dgux AViiON-dgux
DYNIX/ptx dynixptx i386-dynixptx
FreeBSD freebsd freebsd-i386
Linux linux arm-linux
Linux linux i386-linux
Linux linux i586-linux
Linux linux ppc-linux
HP-UX hpux PA-RISC1.1
IRIX irix irix
Mac OS X darwin darwin
MachTen PPC machten powerpc-machten
NeXT 3 next next-fat
NeXT 4 next OPENSTEP-Mach
openbsd openbsd i386-openbsd
OSF1 dec_osf alpha-dec_osf
reliantunix-n svr4 RM400-svr4
SCO_SV sco_sv i386-sco_sv
SINIX-N svr4 RM400-svr4
sn4609 unicos CRAY_C90-unicos
sn6521 unicosmk t3e-unicosmk
sn9617 unicos CRAY_J90-unicos
SunOS solaris sun4-solaris
SunOS solaris i86pc-solaris
SunOS4 sunos sun4-sunos
Because the value of $Config{archname} may depend on the hardware architecture, it can vary more than the value
of $^O.
DOS and Derivatives
Perl has long been ported to Intel-style microcomputers running under systems like PC-DOS, MS-DOS, OS/2, and most
Windows platforms you can bring yourself to mention (except for Windows CE, if you count that). Users familiar
with COMMAND.COM or CMD.EXE style shells should be aware that each of these file specifications may have subtle
differences:
$filespec0 = "c:/foo/bar/file.txt";
$filespec1 = "c:\\foo\\bar\\file.txt";
$filespec2 = 'c:\foo\bar\file.txt';
$filespec3 = 'c:\\foo\\bar\\file.txt';
System calls accept either "/" or "\" as the path separator. However, many command-line utilities of DOS vintage
treat "/" as the option prefix, so may get confused by filenames containing "/". Aside from calling any external
programs, "/" will work just fine, and probably better, as it is more 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-pre-
serving" 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 wrap-
pers 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 sys-
tems, "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 perldos.
� The EMX environment for DOS, OS/2, etc. emx@iaehv.nl,
http://www.leo.org/pub/comp/os/os2/leo/gnu/emx+gcc/index.html or ftp://hobbes.nmsu.edu/pub/os2/dev/emx/ Also
perlos2.
� Build instructions for Win32 in perlwin32, or under the Cygnus environment in perlcygwin.
� The "Win32::*" modules in Win32.
� The ActiveState Pages, http://www.activestate.com/
� The Cygwin environment for Win32; README.cygwin (installed as perlcygwin), http://www.cygwin.com/
� The U/WIN environment for Win32, http://www.research.att.com/sw/tools/uwin/
� Build instructions for OS/2, perlos2
Mac OS
Any module requiring XS compilation is right out for most people, because MacPerl is built using non-free (and
non-cheap!) compilers. Some XS modules that can work with MacPerl are built and 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 popu-
lated 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 architec-
ture, 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 "Car-
bon" version of MacPerl to run under the primary Mac OS X environment. Mac OS X and its Open Source version,
Darwin, both run Unix perl natively.
Also see:
� MacPerl Development, http://dev.macperl.org/ .
� The MacPerl Pages, http://www.macperl.com/ .
� The MacPerl mailing lists, http://lists.perl.org/ .
� MPW, ftp://ftp.apple.com/developer/Tool_Chest/Core_Mac_OS_Tools/
VMS
Perl on VMS is discussed in perlvms in the perl distribution. Perl on VMS can accept either VMS- or Unix-style
file specifications as in either of the following:
$ perl -ne "print if /perl_setup/i" SYS$LOGIN:LOGIN.COM
$ perl -ne "print if /perl_setup/i" /sys$login/login.com
but not a mixture of both as in:
$ perl -ne "print if /perl_setup/i" sys$login:/login.com
Can't open sys$login:/login.com: file specification syntax error
Interacting with Perl from the Digital Command Language (DCL) shell often requires a different set of quotation
marks than Unix shells do. For example:
$ perl -e "print ""Hello, world.\n"""
Hello, world.
There are several ways to wrap your perl scripts in DCL .COM files, if you are so inclined. For example:
$ write sys$output "Hello from DCL!"
$ if p1 .eqs. ""
$ then perl -x 'f$environment("PROCEDURE")
$ else perl -x - 'p1 'p2 'p3 'p4 'p5 'p6 'p7 'p8
$ deck/dollars=""
#!/usr/bin/perl
print "Hello from Perl!\n";
$ 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), perlvms
� vmsperl list, majordomo@perl.org
(Put the words "subscribe vmsperl" in message body.)
� vmsperl on the web, http://www.sidhe.org/vmsperl/index.html
VOS
Perl on VOS is discussed in README.vos in the perl distribution (installed as perlvos). Perl on VOS can accept
either VOS- or Unix-style file specifications as in either of the following:
C<< $ perl -ne "print if /perl_setup/i" >system>notices >>
C<< $ perl -ne "print if /perl_setup/i" /system/notices >>
or even a mixture of both as in:
C<< $ perl -ne "print if /perl_setup/i" >system/notices >>
Even though VOS allows the slash character to appear in object names, because the VOS port of Perl interprets it
as a pathname delimiting character, VOS files, directories, or links whose names 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 rec-
ommended method for building full Perl is with the GNU C compiler and the generally-available version of VOS
POSIX support. See README.vos (installed as perlvos) for restrictions that apply when Perl is built using the
VOS Standard C compiler or the alpha version of VOS POSIX support.
The value of $^O on VOS is "VOS". To determine the architecture that you are running on without resorting to
loading all of %Config you can examine the content of the @INC array like so:
if ($^O =~ /VOS/) {
print "I'm on a Stratus box!\n";
} else {
print "I'm not on a Stratus box!\n";
die;
}
if (grep(/860/, @INC)) {
print "This box is a Stratus XA/R!\n";
} elsif (grep(/7100/, @INC)) {
print "This box is a Stratus HP 7100 or 8xxx!\n";
} elsif (grep(/8000/, @INC)) {
print "This box is a Stratus HP 8xxx!\n";
} else {
print "This box is a Stratus 68K!\n";
}
Also see:
� README.vos (installed as perlvos)
� The VOS mailing list.
There is no specific mailing list for Perl on VOS. You can post comments to the comp.sys.stratus newsgroup,
or subscribe to the general Stratus mailing list. Send a letter with "subscribe Info-Stratus" in the message
body to majordomo@list.stratagy.com.
� VOS Perl on the web at http://ftp.stratus.com/pub/vos/posix/posix.html
EBCDIC Platforms
Recent versions of Perl have been ported to platforms such as OS/400 on AS/400 minicomputers as well as OS/390,
VM/ESA, and BS2000 for S/390 Mainframes. Such computers use EBCDIC character sets internally (usually Character
Code Set ID 0037 for OS/400 and either 1047 or POSIX-BC for S/390 systems). On the mainframe perl currently
works under the "Unix system services for OS/390" (formerly known as OpenEdition), VM/ESA OpenEdition, or the
BS200 POSIX-BC system (BS2000 is supported in perl 5.6 and greater). See perlos390 for details. Note that for
OS/400 there is also a port of Perl 5.8.1/5.9.0 or later to the PASE which is ASCII-based (as opposed to ILE
which is EBCDIC-based), see perlos400.
As of R2.5 of USS for OS/390 and Version 2.3 of VM/ESA these Unix sub-systems do not support the "#!" shebang
trick for script invocation. Hence, on OS/390 and VM/ESA perl scripts can be executed with a header similar to
the following simple script:
: # use perl
eval 'exec /usr/local/bin/perl -S $0 ${1+"$@"}'
if 0;
#!/usr/local/bin/perl # just a comment really
print "Hello from perl!\n";
OS/390 will support the "#!" shebang trick in release 2.8 and beyond. Calls to "system" and backticks can use
POSIX shell syntax on all S/390 systems.
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 "sys-
tem" or backticks must use CL syntax.
On these platforms, bear in mind that the EBCDIC character set may have an effect on what happens with some perl
functions (such as "chr", "pack", "print", "printf", "ord", "sort", "sprintf", "unpack"), as well as bit-fiddling
with ASCII constants using operators like "^", "&" and "|", not to mention dealing with socket interfaces to
ASCII computers (see "Newlines").
Fortunately, most web servers for the mainframe will correctly translate the "\n" in the following statement to
its ASCII equivalent ("\r" is the same under both Unix and OS/390 & VM/ESA):
print "Content-type: text/html\r\n\r\n";
The values of $^O on some of these platforms includes:
uname $^O $Config{'archname'}
--------------------------------------------
OS/390 os390 os390
OS400 os400 os400
POSIX-BC posix-bc BS2000-posix-bc
VM/ESA vmesa vmesa
Some simple tricks for determining if you are running on an EBCDIC platform could include any of the following
(perhaps all):
if ("\t" eq "\05") { print "EBCDIC may be spoken here!\n"; }
if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; }
if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; }
One thing you may not want to rely on is the EBCDIC encoding of punctuation characters since these may differ
from code page to code page (and once your module or script is rumoured to work with EBCDIC, folks will want it
to work with all EBCDIC character sets).
Also see:
� perlos390, README.os390, perlbs2000, README.vmesa, perlebcdic.
� The perl-mvs@perl.org list is for discussion of porting issues as well as general usage issues for all EBCDIC
Perls. Send a message body of "subscribe perl-mvs" to majordomo@perl.org.
� AS/400 Perl information at http://as400.rochester.ibm.com/ as well as on CPAN in the ports/ directory.
Acorn RISC OS
Because Acorns use ASCII with newlines ("\n") in text files as "\012" like Unix, and because Unix filename emula-
tion is turned on by default, most simple scripts will probably work "out of the box". The native filesystem is
modular, and individual filesystems are free to be case-sensitive or insensitive, and are usually case-preserv-
ing. Some native filesystems have name length limits, which file and directory names are silently truncated to
fit. Scripts should be aware that the standard filesystem currently has a name length limit of 10 characters,
with up to 77 items in a directory, but other filesystems may not impose such limitations.
Native filenames are of the form
Filesystem#Special_Field::DiskName.$.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 $. if scripts are not careful.
Logical paths specified by system variables containing comma-separated search lists are also allowed; hence "Sys-
tem:Modules" is a valid filename, and the filesystem will prefix "Modules" with each section of "System$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'} . 'Mod-
ules'". The obvious implication of this is that fully qualified filenames can start with "<>" and should be pro-
tected 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 charac-
ters, Acorn implemented the C compiler to strip the trailing ".c" ".h" ".s" and ".o" suffix from filenames speci-
fied 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 prob-
lems, 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 gener-
ally manages to be 99% right. Of course, the problem remains that scripts cannot rely on any Unix tools being
available, or that any tools found have Unix-like command line arguments.
Extensions and XS are, in theory, buildable by anyone using free tools. In practice, many don't, as users of the
Acorn platform are used to binary distributions. MakeMaker does run, but no available make currently copes with
MakeMaker's makefiles; even if and when this should be fixed, the lack of a Unix-like shell will cause problems
with makefile rules, especially lines of the form "cd sdbm && make all", and anything using quoting.
"RISC OS" is the proper name for the operating system, but the value in $^O is "riscos" (because we don't like
shouting).
Other perls
Perl has been ported to many platforms that do not fit into any of the categories listed above. Some, such as
AmigaOS, Atari MiNT, BeOS, HP MPE/iX, QNX, Plan 9, and VOS, have been well-integrated into the standard Perl
source code kit. You may need to see the ports/ directory on CPAN for 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 perlamiga).
� Atari, README.mint and Guido Flohr's web page http://stud.uni-sb.de/~gufl0000/
� Be OS, README.beos
� HP 300 MPE/iX, README.mpeix and Mark Bixby's web page http://www.bixby.org/mark/perlix.html
� A free perl5-based PERL.NLM for Novell Netware is available in precompiled binary and source code form from
http://www.novell.com/ as well as from CPAN.
� Plan 9, README.plan9
FUNCTION IMPLEMENTATIONS
Listed below are functions that are either completely unimplemented or else have been implemented differently on
various platforms. Following each description will be, in parentheses, a list of platforms that the description
applies to.
The list may well be incomplete, or even wrong in some places. When in doubt, consult the platform-specific
README files in the Perl source distribution, and any other documentation resources accompanying a given port.
Be aware, moreover, that even among Unix-ish systems there are variations.
For many functions, you can also query %Config, exported by default from the Config module. For example, to
check whether the platform has the "lstat" call, check $Config{d_lstat}. See Config for a full description of
available variables.
Alphabetical Listing of Perl Functions
-X "-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 pro-
tections. (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)
atan2 Y,X
Due to issues with various CPUs, math libraries, compilers, and standards, results for "atan2()" may vary
depending on any combination of the above. Perl attempts to conform to the Open Group/IEEE standards for
the results returned from "atan2()", but cannot force the issue if the system Perl is run on does not
allow it. (Tru64, HP-UX 10.20)
The current version of the standards for "atan2()" is available at <http://www.open-
group.org/onlinepubs/009695399/functions/atan2.html>.
atan2 Due to issues with various CPUs, math libraries, compilers, and standards, results for "atan2()" may vary
depending on any combination of the above. Perl attempts to conform to the Open Group/IEEE standards for
the results returned from "atan2()", but cannot force the issue if the system Perl is run on does not
allow it. (Tru64, HP-UX 10.20)
The current version of the standards for "atan2()" is available at <http://www.open-
group.org/onlinepubs/009695399/functions/atan2.html>.
binmode Meaningless. (Mac OS, RISC OS)
Reopens file and restores pointer; if function fails, underlying filehandle may be closed, or pointer may
be in a different position. (VMS)
The value returned by "tell" may be affected after the call, and the filehandle may be flushed. (Win32)
chmod Only limited meaning. Disabling/enabling write permission is mapped to locking/unlocking the file.
(Mac OS)
Only good for changing "owner" read-write access, "group", and "other" bits are meaningless. (Win32)
Only good for changing "owner" and "other" read-write access. (RISC OS)
Access permissions are mapped onto VOS access-control list changes. (VOS)
The actual permissions set depend on the value of the "CYGWIN" in the SYSTEM environment settings. (Cyg-
win)
chown Not implemented. (Mac OS, Win32, Plan 9, RISC OS, VOS)
Does nothing, but won't fail. (Win32)
chroot Not implemented. (Mac OS, Win32, VMS, Plan 9, RISC OS, VOS, VM/ESA)
crypt May not be available if library or source was not provided when building perl. (Win32)
Not implemented. (VOS)
dbmclose
Not implemented. (VMS, Plan 9, VOS)
dbmopen Not implemented. (VMS, Plan 9, VOS)
dump Not useful. (Mac OS, RISC OS)
Not implemented. (Win32)
Invokes VMS debugger. (VMS)
exec Not implemented. (Mac OS)
Implemented via Spawn. (VM/ESA)
Does not automatically flush output handles on some platforms. (SunOS, Solaris, HP-UX)
exit Emulates UNIX exit() (which considers "exit 1" to indicate an error) by mapping the 1 to SS$_ABORT(44).
This behavior may be overridden with the pragma "use vmsish 'exit'". As with the CRTL's exit() function,
"exit 0" is also mapped to an exit status of SS$_NORMAL(1); this mapping cannot be overridden. Any
other argument to exit() is used directly as Perl's exit status. (VMS)
fcntl Not implemented. (Win32, VMS)
flock Not implemented (Mac OS, VMS, RISC OS, VOS).
Available only on Windows NT (not on Windows 95). (Win32)
fork Not implemented. (Mac OS, AmigaOS, RISC OS, VOS, VM/ESA, VMS)
Emulated using multiple interpreters. See perlfork. (Win32)
Does not automatically flush output handles on some platforms. (SunOS, Solaris, HP-UX)
getlogin
Not implemented. (Mac OS, RISC OS)
getpgrp Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)
getppid Not implemented. (Mac OS, Win32, RISC OS)
getpriority
Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS, VM/ESA)
getpwnam
Not implemented. (Mac OS, Win32)
Not useful. (RISC OS)
getgrnam
Not implemented. (Mac OS, Win32, VMS, RISC OS)
getnetbyname
Not implemented. (Mac OS, Win32, Plan 9)
getpwuid
Not implemented. (Mac OS, Win32)
Not useful. (RISC OS)
getgrgid
Not implemented. (Mac OS, Win32, VMS, RISC OS)
getnetbyaddr
Not implemented. (Mac OS, Win32, Plan 9)
getprotobynumber
Not implemented. (Mac OS)
getservbyport
Not implemented. (Mac OS)
getpwent
Not implemented. (Mac OS, Win32, VM/ESA)
getgrent
Not implemented. (Mac OS, Win32, VMS, VM/ESA)
gethostbyname
"gethostbyname('localhost')" does not work everywhere: you may have to use "gethostbyname('127.0.0.1')".
(Mac OS, Irix 5)
gethostent
Not implemented. (Mac OS, Win32)
getnetent
Not implemented. (Mac OS, Win32, Plan 9)
getprotoent
Not implemented. (Mac OS, Win32, Plan 9)
getservent
Not implemented. (Win32, Plan 9)
sethostent
Not implemented. (Mac OS, Win32, Plan 9, RISC OS)
setnetent
Not implemented. (Mac OS, Win32, Plan 9, RISC OS)
setprotoent
Not implemented. (Mac OS, Win32, Plan 9, RISC OS)
setservent
Not implemented. (Plan 9, Win32, RISC OS)
endpwent
Not implemented. (Mac OS, MPE/iX, VM/ESA, Win32)
endgrent
Not implemented. (Mac OS, MPE/iX, RISC OS, VM/ESA, VMS, Win32)
endhostent
Not implemented. (Mac OS, Win32)
endnetent
Not implemented. (Mac OS, Win32, Plan 9)
endprotoent
Not implemented. (Mac OS, Win32, Plan 9)
endservent
Not implemented. (Plan 9, Win32)
getsockopt SOCKET,LEVEL,OPTNAME
Not implemented. (Plan 9)
glob This operator is implemented via the File::Glob extension on most platforms. See File::Glob for porta-
bility information.
gmtime Same portability caveats as localtime.
ioctl FILEHANDLE,FUNCTION,SCALAR
Not implemented. (VMS)
Available only for socket handles, and it does what the ioctlsocket() call in the Winsock API does.
(Win32)
Available only for socket handles. (RISC OS)
kill "kill(0, LIST)" is implemented for the sake of taint checking; use with other signals is unimplemented.
(Mac OS)
Not implemented, hence not useful for taint checking. (RISC OS)
"kill()" doesn't have the semantics of "raise()", i.e. it doesn't send a signal to the 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)
link Not implemented. (Mac OS, MPE/iX, VMS, RISC OS)
Link count not updated because hard links are not quite that hard (They are sort of half-way between hard
and soft links). (AmigaOS)
Hard links are implemented on Win32 (Windows NT and Windows 2000) under NTFS only.
localtime
Because Perl currently relies on the native standard C localtime() function, it is only safe to use times
between 0 and (2**31)-1. Times outside this range may result in unexpected behavior depending on your
operating system's implementation of localtime().
lstat Not implemented. (VMS, RISC OS)
Return values (especially for device and inode) may be bogus. (Win32)
msgctl
msgget
msgsnd
msgrcv Not implemented. (Mac OS, Win32, VMS, Plan 9, RISC OS, VOS)
open The "|" variants are supported only if ToolServer is installed. (Mac OS)
open to "|-" and "-|" are unsupported. (Mac OS, Win32, RISC OS)
Opening a process does not automatically flush output handles on some platforms. (SunOS, Solaris, HP-UX)
pipe Very limited functionality. (MiNT)
readlink
Not implemented. (Win32, VMS, RISC OS)
rename Can't move directories between directories on different logical volumes. (Win32)
select Only implemented on sockets. (Win32, VMS)
Only reliable on sockets. (RISC OS)
Note that the "select FILEHANDLE" form is generally portable.
semctl
semget
semop Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)
setgrent
Not implemented. (Mac OS, MPE/iX, VMS, Win32, RISC OS)
setpgrp Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)
setpriority
Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)
setpwent
Not implemented. (Mac OS, MPE/iX, Win32, RISC OS)
setsockopt
Not implemented. (Plan 9)
shmctl
shmget
shmread
shmwrite
Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)
sockatmark
A relatively recent addition to socket functions, may not be implemented even in UNIX platforms.
socketpair
Not implemented. (Win32, VMS, RISC OS, VOS, VM/ESA)
stat Platforms that do not have rdev, blksize, or blocks will return these as , so numeric 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 reli-
able. (RISC OS)
dev, rdev, blksize, and blocks are not available. inode is not meaningful and will differ between stat
calls on the same file. (os2)
some versions of cygwin when doing a stat("foo") and if not finding it may then attempt to
stat("foo.exe") (Cygwin)
symlink Not implemented. (Win32, VMS, RISC OS)
syscall Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS, VM/ESA)
sysopen The traditional "0", "1", and "2" MODEs are implemented with different numeric values on some systems.
The flags exported by "Fcntl" (O_RDONLY, O_WRONLY, O_RDWR) should work everywhere though. (Mac OS,
OS/390, VM/ESA)
system In general, do not assume the UNIX/POSIX semantics that you can shift $? right by eight to get the exit
value, or that "$? & 127" would give you the number of the signal that 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 ter-
minate. 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, pro-
viding 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 perlvms. (VMS)
times Only the first entry returned is nonzero. (Mac OS)
"cumulative" times will be bogus. On anything other than Windows NT or Windows 2000, "system" time will
be bogus, and "user" time is actually the time returned by the clock() function in the C runtime library.
(Win32)
Not useful. (RISC OS)
truncate
Not implemented. (Older versions of VMS)
Truncation to zero-length only. (VOS)
If a FILEHANDLE is supplied, it must be writable and opened in append mode (i.e., use "open(FH, '>>file-
name')" or "sysopen(FH,...,O_APPEND|O_RDWR)". If a filename is supplied, it should not be held open
elsewhere. (Win32)
umask Returns undef where unavailable, as of version 5.005.
"umask" works but the correct permissions are set only when the file is finally closed. (AmigaOS)
utime Only the modification time is updated. (BeOS, Mac OS, VMS, RISC OS)
May not behave as expected. Behavior depends on the C runtime library's implementation of utime(), and
the filesystem being used. The FAT filesystem typically does not support an "access time" field, and it
may limit timestamps to a granularity of two seconds. (Win32)
wait
waitpid Not implemented. (Mac OS, VOS)
Can only be applied to process handles returned for processes spawned using "system(1, ...)" or pseudo
processes created with "fork()". (Win32)
Not useful. (RISC OS)
Supported Platforms
As of September 2003 (the Perl release 5.8.1), the following platforms are able to build Perl from the standard
source code distribution available at http://www.cpan.org/src/index.html
AIX
BeOS
BSD/OS (BSDi)
Cygwin
DG/UX
DOS DJGPP 1)
DYNIX/ptx
EPOC R5
FreeBSD
HI-UXMPP (Hitachi) (5.8.0 worked but we didn't know it)
HP-UX
IRIX
Linux
LynxOS
Mac OS Classic
Mac OS X (Darwin)
MPE/iX
NetBSD
NetWare
NonStop-UX
ReliantUNIX (formerly SINIX)
OpenBSD
OpenVMS (formerly VMS)
Open UNIX (Unixware) (since Perl 5.8.1/5.9.0)
OS/2
OS/400 (using the PASE) (since Perl 5.8.1/5.9.0)
PowerUX
POSIX-BC (formerly BS2000)
QNX
Solaris
SunOS 4
SUPER-UX (NEC)
SVR4
Tru64 UNIX (formerly DEC OSF/1, Digital UNIX)
UNICOS
UNICOS/mk
UTS
VOS
Win95/98/ME/2K/XP 2)
WinCE
z/OS (formerly OS/390)
VM/ESA
1) in DOS mode either the DOS or OS/2 ports can be used
2) compilers: Borland, MinGW (GCC), VC6
The following platforms worked with the previous releases (5.6 and 5.7), but we did not manage either to fix or
to test these in time for the 5.8.1 release. There is a very good chance that many of these will work fine with
the 5.8.1.
DomainOS
Hurd
MachTen
PowerMAX
SCO SV
Unixware
Windows 3.1
Known to be broken for 5.8.0 and 5.8.1 (but 5.6.1 and 5.7.2 can be used):
AmigaOS
The following platforms have been known to build Perl from source in the past (5.005_03 and earlier), but we
haven't been able to verify their status for the current release, either because the 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 dis-
tributions.
RELATED
perlaix, perlamiga, perlapollo, perlbeos, perlbs2000, perlce, perlcygwin, perldgux, perldos, perlepoc, per-
lebcdic, perlfreebsd, perlhurd, perlhpux, perlirix, perlmachten, perlmacos, perlmacosx, perlmint, perlmpeix,
perlnetware, perlos2, perlos390, perlos400, perlplan9, perlqnx, perlsolaris, perltru64, perlunicode, perlvmesa,
perlvms, perlvos, perlwin32, and Win32.
AUTHORS / CONTRIBUTORS
Abigail <abigail@foad.org>, Charles Bailey <bailey@newman.upenn.edu>, Graham Barr <gbarr@pobox.com>, Tom Chris-
tiansen <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. Koenig <a.koenig@mind.de>, Markus Laker <mlaker@contax.co.uk>, Andrew M. Langmead <aml@world.std.com>, Larry
Moore <ljmoore@freespace.net>, Paul Moore <Paul.Moore@uk.origin-it.com>, Chris Nandor <pudge@pobox.com>, Matthias
Neeracher <neeracher@mac.com>, Philip Newton <pne@cpan.org>, Gary Ng <71564.1743@CompuServe.COM>, Tom Phoenix
<rootbeer@teleport.com>, Andre Pirard <A.Pirard@ulg.ac.be>, Peter Prymmer <pvhp@forte.com>, Hugo van der Sanden
<hv@crypt0.demon.co.uk>, Gurusamy Sarathy <gsar@activestate.com>, Paul J. Schinder <schinder@pobox.com>, Michael
G Schwern <schwern@pobox.com>, Dan Sugalski <dan@sidhe.org>, Nathan Torkington <gnat@frii.com>.
CATEGORY