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PERLPORT(1) Perl Programmers Reference Guide PERLPORT(1)
NAME
perlport - Writing portable Perl
DESCRIPTION
Perl runs on numerous operating systems. While most of
them share much in common, they also have their own unique
features.
This document is meant to help you to find out what con-
stitutes portable Perl code. That way once you make a
decision to write portably, you know where the lines are
drawn, and you can stay within them.
There is a tradeoff between taking full advantage of one
particular type of computer and taking advantage of a full
range of them. Naturally, as you broaden your range and
become more diverse, the common factors drop, and you are
left with an increasingly smaller area of common ground in
which you can operate to accomplish a particular task.
Thus, when you begin attacking a problem, it is important
to consider under which part of the tradeoff curve you
want to operate. Specifically, you must decide whether it
is important that the task that you are coding have the
full generality of being portable, or whether to just get
the job done right now. This is the hardest choice to be
made. The rest is easy, because Perl provides many
choices, whichever way you want to approach your problem.
Looking at it another way, writing portable code is usu-
ally about willfully limiting your available choices.
Naturally, it takes discipline and sacrifice to do that.
The product of portability and convenience may be a con-
stant. 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 lan-
guage to glue Unix tools together, or to prototype a
Macintosh application, or to manage the Windows reg-
istry. 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 cre-
ate portable Perl code. It isn't. Perl tries its
level-best to bridge the gaps between what's available
on different platforms, and all the means available to
use those features. Thus almost all Perl code runs on
any machine without modification. But there are some
significant issues in writing portable code, and this
document is entirely about those issues.
Here's the general rule: When you approach a task commonly
done using a whole range of platforms, think about writing
portable code. That way, you don't sacrifice much by way
of the implementation choices you can avail yourself of,
and at the same time you can give your users lots of plat-
form choices. On the other hand, when you have to take
advantage of some unique feature of a particular platform,
as is often the case with systems programming (whether for
Unix, Windows, Mac OS, VMS, etc.), consider writing plat-
form-specific code.
When the code will run on only two or three operating sys-
tems, 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 IMPLEMENTA-
TIONS").
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 ("
").
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", depend-
ing on whether you're reading or writing. Unix does the
same thing on ttys in canonical mode. "\015\012" is com-
monly referred to as CRLF.
A common cause of unportable programs is the misuse of
chop() to trim newlines:
# XXX UNPORTABLE!
while() {
chop;
@array = split(/:/);
#...
}
You can get away with this on Unix and Mac OS (they have a
single character end-of-line), but the same program will
break under DOSish perls because you're only chop()ing
half the end-of-line. Instead, chomp() should be used to
trim newlines. The Dunce::Files module can help audit
your code for misuses of chop().
When dealing with binary files (or text files in binary
mode) be sure to explicitly set $/ to the appropriate
value for your file format before using chomp().
Because of the "text" mode translation, DOSish perls have
limitations in using "seek" and "tell" on a file accessed
in "text" mode. Stick to "seek"-ing to locations you got
from "tell" (and no others), and you are usually free to
use "seek" and "tell" even in "text" mode. Using "seek"
or "tell" or other file operations may be non-portable.
If you use "binmode" on a file, however, you can usually
"seek" and "tell" with arbitrary values in safety.
A common misconception in socket programming is that "\n"
eq "\012" everywhere. When using protocols such as common
Internet protocols, "\012" and "\015" are called for
specifically, and the values of the logical "\n" and "\r"
(carriage return) are not reliable.
print SOCKET "Hi there, client!\r\n"; # WRONG
print SOCKET "Hi there, client!\015\012"; # RIGHT
However, using "\015\012" (or "\cM\cJ", or "\x0D\x0A") can
be tedious and unsightly, as well as confusing to those
maintaining the code. As such, the Socket module supplies
the Right Thing for those who want it.
use Socket qw(:DEFAULT :crlf);
print SOCKET "Hi there, client!$CRLF" # RIGHT
When reading from a socket, remember that the default
input record separator $/ is "\n", but robust socket code
will recognize as either "\012" or "\015\012" as end of
line:
while () {
# ...
}
Because both CRLF and LF end in LF, the input record sepa-
rator can be set to LF and any CR stripped later. Better
to write:
use Socket qw(:DEFAULT :crlf);
local($/) = LF; # not needed if $/ is already \012
while () {
s/$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 numbers in
binary format from one CPU architecture to another, usu-
ally 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 num-
bers. 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 "<" modi-
fiers 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 unpack-
ing 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 plat-
forms 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). Keep-
ing all data as text significantly simplifies matters.
The v-strings are portable only up to v2147483647
(0x7FFFFFFF), that's how far EBCDIC, or more precisely
UTF-EBCDIC will go.
Files and Filesystems
Most platforms these days structure files in a hierarchi-
cal fashion. So, it is reasonably safe to assume that all
platforms support the notion of a "path" to uniquely iden-
tify a file on the system. How that path is really writ-
ten, though, differs considerably.
Although similar, file path specifications differ between
Unix, Windows, Mac OS, OS/2, VMS, VOS, RISC OS, and proba-
bly 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 sepa-
rator. The native pathname characters greater-than,
less-than, number-sign, and percent-sign are always
accepted.
RISC OS perl can emulate Unix filenames with "/" as path
separator, or go native and use "." for path separator and
":" to signal filesystems and disk names.
Don't assume UNIX filesystem access semantics: that read,
write, and execute are all the permissions there are, and
even if they exist, that their semantics (for example what
do r, w, and x mean on a directory) are the UNIX ones.
The various UNIX/POSIX compatibility layers usually try to
make interfaces like chmod() work, but sometimes there
simply is no good mapping.
If all this is intimidating, have no (well, maybe only a
little) fear. There are modules that can help. The
File::Spec modules provide methods to do the Right Thing
on whatever platform happens to be running the program.
use File::Spec::Functions;
chdir(updir()); # go up one directory
$file = catfile(curdir(), 'temp', 'file.txt');
# on Unix and Win32, './temp/file.txt'
# on Mac OS, ':temp:file.txt'
# on VMS, '[.temp]file.txt'
File::Spec is available in the standard distribution as of
version 5.004_05. File::Spec::Functions is only in
File::Spec 0.7 and later, and some versions of perl come
with version 0.6. If File::Spec is not updated to 0.7 or
later, you must use the object-oriented interface from
File::Spec (or upgrade File::Spec).
In general, production code should not have file paths
hardcoded. Making them user-supplied or read from a 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 distribu-
tion, 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 plat-
forms 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 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 tolerated,
some utilities might become confused by such whitespace.
Many systems (DOS, VMS) cannot have more than one "." in
their filenames.
Don't assume ">" won't be the first character of a file-
name. 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 sepa-
rating 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 lead-
ing 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 low-
ercased 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 usu-
ally 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 filesys-
tems you need write/modify permission also (or even just)
in the file/directory itself. In some filesystems (AFS,
DFS) the permission to add/delete directory entries is a
completely separate permission.
Don't assume that a single "unlink" completely gets rid of
the file: some filesystems (most notably the ones in VMS)
have versioned filesystems, and unlink() removes only the
most recent one (it doesn't remove all the versions
because by default the native tools on those platforms
remove just the most recent version, too). The portable
idiom to remove all the versions of a file is
1 while unlink "file";
This will terminate if the file is undeleteable for some
reason (protected, not there, and so on).
Don't count on a specific environment variable existing in
%ENV. Don't count on %ENV entries being case-sensitive,
or even case-preserving. Don't try to clear %ENV by say-
ing "%ENV = ();", or, if you really have to, make it con-
ditional on "$^O ne 'VMS'" since in VMS the %ENV table is
much more than a per-process key-value string table.
Don't count on signals or %SIG for anything.
Don't count on filename globbing. Use "opendir", "read-
dir", and "closedir" instead.
Don't count on per-program environment variables, or per-
program current directories.
Don't count on specific values of $!, neither numeric nor
especially the strings values-- users may switch their
locales causing error messages to be translated into their
languages. If you can trust a POSIXish environment, you
can portably use the symbols defined by the Errno module,
like ENOENT. And don't trust on the values of $! at all
except immediately after a failed system call.
Command names versus file pathnames
Don't assume that the name used to invoke a command or
program with "system" or "exec" can also be used to test
for the existence of the file that holds the executable
code for that command or program. First, many systems
have "internal" commands that are built-in to the shell or
OS and while these commands can be invoked, there is no
corresponding file. Second, some operating systems (e.g.,
Cygwin, DJGPP, OS/2, and VOS) have required suffixes for
executable files; these suffixes are generally permitted
on the command name but are not required. Thus, a command
like "perl" might exist in a file named "perl",
"perl.exe", or "perl.pm", depending on the operating sys-
tem. 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 pro-
cessing 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 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 com-
mand) 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 sup-
ported on most platforms (though many of them do not sup-
port any type of forking). The problem with using them
arises from what you invoke them on. External tools are
often named differently on different platforms, may not be
available in the same location, might accept different
arguments, can behave differently, and often present their
results in a platform-dependent way. Thus, you should
seldom depend on them to produce consistent results. (Then
again, if you're calling netstat -a, you probably don't
expect it to run on both Unix and CP/M.)
One especially common bit of Perl code is opening a pipe
to sendmail:
open(MAIL, '|/usr/lib/sendmail -t')
or die "cannot fork sendmail: $!";
This is fine for systems programming when sendmail is
known to be available. But it is not fine for many non-
Unix systems, and even some Unix systems that may not have
sendmail installed. If a portable solution is needed, see
the various distributions on CPAN that deal with it.
Mail::Mailer and Mail::Send in the MailTools distribution
are commonly used, and provide several mailing methods,
including mail, sendmail, and direct SMTP (via Net::SMTP)
if a mail transfer agent is not available. Mail::Sendmail
is a standalone module that provides simple, platform-
independent mailing.
The Unix System V IPC ("msg*(), sem*(), shm*()") is not
available even on all Unix platforms.
Do not use either the bare result of "pack("N", 10, 20,
30, 40)" or bare v-strings (such as "v10.20.30.40") to
represent IPv4 addresses: both forms just pack the four
bytes into network order. That this would be equal to the
C language "in_addr" struct (which is what the socket code
internally uses) is not guaranteed. To be portable use
the routines of the Socket extension, such as
"inet_aton()", "inet_ntoa()", and "sockaddr_in()".
The rule of thumb for portable code is: Do it all in
portable Perl, or use a module (that may internally 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 representa-
tion. 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 rep-
resentation (like "1987-12-18") can be easily converted
into an OS-specific value using a module like Date::Parse.
An array of values, such as those returned by "localtime",
can be converted to an OS-specific representation using
Time::Local.
When calculating specific times, such as for tests in time
or date modules, it may be appropriate to calculate an
offset for the epoch.
require Time::Local;
$offset = Time::Local::timegm(0, 0, 0, 1, 0, 70);
The value for $offset in Unix will be 0, but in Mac OS
will be some large number. $offset can then be added to a
Unix time value to get what should be the proper value on
any system.
On Windows (at least), you shouldn't pass a negative value
to "gmtime" or "localtime".
Character sets and character encoding
Assume very little about character sets.
Assume nothing about numerical values ("ord", "chr") of
characters. Do not use explicit code point ranges (like
\xHH-\xHH); use for example symbolic character classes
like "[:print:]".
Do not assume that the alphabetic characters are encoded
contiguously (in the numeric sense). There may be gaps.
Do not assume anything about the ordering of the charac-
ters. 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 inter-
laced 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 con-
sider 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 exam-
ple 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" nota-
tion 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 con-
strained (or missing!) virtual memory systems then you
want to be especially mindful of avoiding wasteful con-
structs such as:
# NOTE: this is no longer "bad" in perl5.005
for (0..10000000) {} # bad
for (my $x = 0; $x <= 10000000; ++$x) {} # good
@lines = ; # bad
while () {$file .= $_} # sometimes bad
$file = join('', ); # 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 secu-
rity, 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 usu-
ally best to know what type of system you will be running
under so that you can write code explicitly for that plat-
form (or class of platforms).
Don't assume the UNIX filesystem access semantics: the
operating system or the filesystem may be using some ACL
systems, which are richer languages than the usual rwx.
Even if the rwx exist, their semantics might be different.
(From security viewpoint testing for permissions before
attempting to do something is silly anyway: if one tries
this, there is potential for race conditions-- someone or
something might change the permissions between the permis-
sions check and the actual operation. Just try the opera-
tion.)
Don't assume the UNIX user and group semantics: espe-
cially, 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-spe-
cific 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 differ-
entiate 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 volun-
teers 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 devel-
opers fix any problems in their code that crop up because
of lack of testing on other platforms; two, to provide
users with information about whether a given module works
on a given platform.
Also see:
o Mailing list: cpan-testers@perl.org
o Testing results: http://testers.cpan.org/
PLATFORMS
As of version 5.002, Perl is built with a $^O variable
that indicates the operating system it was built on. This
was implemented to help speed up code that would otherwise
have to "use Config" and use the value of $Config{osname}.
Of course, to get more detailed information about the sys-
tem, 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/ direc-
tory in the source code kit). On most of these systems,
the value of $^O (hence $Config{'osname'}, too) is deter-
mined 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 test-
ing 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 famil-
iar with COMMAND.COM or CMD.EXE style shells should be
aware that each of these file specifications may have sub-
tle 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 separa-
tor. 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-preserv-
ing" HPFS (OS/2) and NTFS (NT) filesystems you may have to
be careful about case returned with functions like "read-
dir" or used with functions like "open" or "opendir".
DOS also treats several filenames as special, such as AUX,
PRN, NUL, CON, COM1, LPT1, LPT2, etc. Unfortunately,
sometimes these filenames won't even work if you include
an explicit directory prefix. It is best to avoid such
filenames, if you want your code to be portable to DOS and
its derivatives. It's hard to know what these all are,
unfortunately.
Users of these operating systems may also wish to make use
of scripts such as pl2bat.bat or pl2cmd to put wrappers
around your scripts.
Newline ("\n") is translated as "\015\012" by STDIO when
reading from and writing to files (see "Newlines"). "bin-
mode(FILEHANDLE)" will keep "\n" translated as "\012" for
that filehandle. Since it is a no-op on other systems,
"binmode" should be used for cross-platform code that
deals with binary data. That's assuming you realize in
advance that your data is in binary. General-purpose pro-
grams should often assume nothing about their data.
The $^O variable and the $Config{archname} values for var-
ious 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:
o The djgpp environment for DOS, http://www.delo-
rie.com/djgpp/ and perldos.
o 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 per-
los2.
o Build instructions for Win32 in perlwin32, or under
the Cygnus environment in perlcygwin.
o The "Win32::*" modules in Win32.
o The ActiveState Pages, http://www.activestate.com/
o The Cygwin environment for Win32; README.cygwin
(installed as perlcygwin), http://www.cygwin.com/
o The U/WIN environment for Win32,
http://www.research.att.com/sw/tools/uwin/
o Build instructions for OS/2, perlos2
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 architecture,
version, or whether the application or MPW tool version is
running, check:
$is_app = $MacPerl::Version =~ /App/;
$is_tool = $MacPerl::Version =~ /MPW/;
($version) = $MacPerl::Version =~ /^(\S+)/;
$is_ppc = $MacPerl::Architecture eq 'MacPPC';
$is_68k = $MacPerl::Architecture eq 'Mac68K';
Mac OS X, based on NeXT's OpenStep OS, runs MacPerl
natively, under the "Classic" environment. There is no
"Carbon" version of MacPerl to run under the primary Mac
OS X environment. Mac OS X and its Open Source version,
Darwin, both run Unix perl natively.
Also see:
o MacPerl Development, http://dev.macperl.org/ .
o The MacPerl Pages, http://www.macperl.com/ .
o The MacPerl mailing lists, http://lists.perl.org/ .
o MPW, ftp://ftp.apple.com/devel-
oper/Tool_Chest/Core_Mac_OS_Tools/
VMS
Perl on VMS is discussed in perlvms in the perl distribu-
tion. Perl on VMS can accept either VMS- or Unix-style
file specifications as in either of the following:
$ perl -ne "print if /perl_setup/i" SYS$LOGIN:LOGIN.COM
$ perl -ne "print if /perl_setup/i" /sys$login/login.com
but not a mixture of both as in:
$ perl -ne "print if /perl_setup/i" sys$login:/login.com
Can't open sys$login:/login.com: file specification syntax error
Interacting with Perl from the Digital Command Language
(DCL) shell often requires a different set of quotation
marks than Unix shells do. For example:
$ perl -e "print ""Hello, world.\n"""
Hello, world.
There are several ways to wrap your perl scripts in DCL
.COM files, if you are so inclined. For example:
$ write sys$output "Hello from DCL!"
$ if p1 .eqs. ""
$ then perl -x 'f$environment("PROCEDURE")
$ else perl -x - 'p1 'p2 'p3 'p4 'p5 'p6 'p7 'p8
$ deck/dollars="__END__"
#!/usr/bin/perl
print "Hello from Perl!\n";
__END__
$ endif
Do take care with "$ ASSIGN/nolog/user SYS$COMMAND:
SYS$INPUT" if your perl-in-DCL script expects to do things
like "$read = ;".
Filenames are in the format "name.extension;version". The
maximum length for filenames is 39 characters, and the
maximum length for extensions is also 39 characters. Ver-
sion is a number from 1 to 32767. Valid characters are
"/[A-Z0-9$_-]/".
VMS's RMS filesystem is case-insensitive and does not pre-
serve 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 help-
ful 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 sup-
ported.
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 $^O is...\n";
}
On VMS, perl determines the UTC offset from the "SYS$TIME-
ZONE_DIFFERENTIAL" logical name. Although the VMS epoch
began at 17-NOV-1858 00:00:00.00, calls to "localtime" are
adjusted to count offsets from 01-JAN-1970 00:00:00.00,
just like Unix.
Also see:
o README.vms (installed as README_vms), perlvms
o vmsperl list, majordomo@perl.org
(Put the words "subscribe vmsperl" in message body.)
o vmsperl on the web,
http://www.sidhe.org/vmsperl/index.html
VOS
Perl on VOS is discussed in README.vos in the perl distri-
bution (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, directo-
ries, or links whose names contain a slash character can-
not 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 recom-
mended 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 sup-
port.
The value of $^O on VOS is "VOS". To determine the archi-
tecture that you are running on without resorting to load-
ing all of %Config you can examine the content of the @INC
array like so:
if ($^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:
o README.vos (installed as perlvos)
o The VOS mailing list.
There is no specific mailing list for Perl on VOS.
You can post comments to the comp.sys.stratus news-
group, or subscribe to the general Stratus mailing
list. Send a letter with "subscribe Info-Stratus" in
the message body to majordomo@list.stratagy.com.
o VOS Perl on the web at http://ftp.stra-
tus.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 "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-fid-
dling 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 $Config{'archname'}
--------------------------------------------
OS/390 os390 os390
OS400 os400 os400
POSIX-BC posix-bc BS2000-posix-bc
VM/ESA vmesa vmesa
Some simple tricks for determining if you are running on
an EBCDIC platform could include any of the following
(perhaps all):
if ("\t" eq "\05") { print "EBCDIC may be spoken here!\n"; }
if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; }
if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; }
One thing you may not want to rely on is the EBCDIC encod-
ing of punctuation characters since these may differ from
code page to code page (and once your module or script is
rumoured to work with EBCDIC, folks will want it to work
with all EBCDIC character sets).
Also see:
o perlos390, README.os390, perlbs2000, README.vmesa,
perlebcdic.
o The perl-mvs@perl.org list is for discussion of port-
ing issues as well as general usage issues for all
EBCDIC Perls. Send a message body of "subscribe
perl-mvs" to majordomo@perl.org.
o AS/400 Perl information at
http://as400.rochester.ibm.com/ as well as on CPAN in
the ports/ directory.
Acorn RISC OS
Because Acorns use ASCII with newlines ("\n") in text
files as "\012" like Unix, and because Unix filename emu-
lation is turned on by default, most simple scripts will
probably work "out of the box". The native filesystem is
modular, and individual filesystems are free to be case-
sensitive or insensitive, and are usually case-preserving.
Some native filesystems have name length limits, which
file and directory names are silently truncated to fit.
Scripts should be aware that the standard filesystem cur-
rently has a name length limit of 10 characters, with up
to 77 items in a directory, but other filesystems may not
impose such limitations.
Native filenames are of the form
Filesystem#Special_Field::DiskName.$.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.$.File" ne 'ADFS::Hard-
Disk.$.File'" and that the second stage of "$" interpola-
tion 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$Path" contains a single item list. The filesystem
will also expand system variables in filenames if enclosed
in angle brackets, so ".Modules" would look
for the file "$ENV{'System$Dir'} . 'Modules'". The obvi-
ous implication of this is that fully qualified filenames
can start with "<>" and should be protected when "open" is
used for input.
Because "." was in use as a directory separator and file-
names could not be assumed to be unique after 10 charac-
ters, Acorn implemented the C compiler to strip the trail-
ing ".c" ".h" ".s" and ".o" suffix from filenames speci-
fied in source code and store the respective files in sub-
directories named after the suffix. Hence files are
translated:
foo.h h.foo
C:foo.h C:h.foo (logical path variable)
sys/os.h sys.h.os (C compiler groks Unix-speak)
10charname.c c.10charname
10charname.o o.10charname
11charname_.c c.11charname (assuming filesystem truncates at 10)
The Unix emulation library's translation of filenames to
native assumes that this sort of translation is required,
and it allows a user-defined list of known suffixes that
it will transpose in this fashion. This may seem trans-
parent, but consider that with these rules "foo/bar/baz.h"
and "foo/bar/h/baz" both map to "foo.bar.h.baz", and that
"readdir" and "glob" cannot and do not attempt to emulate
the reverse mapping. Other "."'s in filenames are trans-
lated to "/".
As implied above, the environment accessed through %ENV is
global, and the convention is that program specific envi-
ronment variables are of the form "Program$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 pro-
grams (and Makefiles) cannot assume that they can spawn a
child process which can change the current directory with-
out affecting its parent (and everyone else for that mat-
ter).
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
".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 any-
thing 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 prob-
lems 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 shout-
ing).
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 val-
ues in the "OTHER" category include:
OS $^O $Config{'archname'}
------------------------------------------
Amiga DOS amigaos m68k-amigos
BeOS beos
MPE/iX mpeix PA-RISC1.1
See also:
o Amiga, README.amiga (installed as perlamiga).
o Atari, README.mint and Guido Flohr's web page
http://stud.uni-sb.de/~gufl0000/
o Be OS, README.beos
o HP 300 MPE/iX, README.mpeix and Mark Bixby's web page
http://www.bixby.org/mark/perlix.html
o A free perl5-based PERL.NLM for Novell Netware is
available in precompiled binary and source code form
from http://www.novell.com/ as well as from CPAN.
o Plan 9, README.plan9
FUNCTION IMPLEMENTATIONS
Listed below are functions that are either completely
unimplemented or else have been implemented differently on
various platforms. Following each description will be, in
parentheses, a list of platforms that the description
applies to.
The list may well be incomplete, or even wrong in some
places. When in doubt, consult the platform-specific
README files in the Perl source distribution, and any
other documentation resources accompanying a given port.
Be aware, moreover, that even among Unix-ish systems there
are variations.
For many functions, you can also query %Config, exported
by default from the Config module. For example, to check
whether the platform has the "lstat" call, check $Con-
fig{d_lstat}. See Config for a full description of avail-
able 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 protections. (VMS)
"-s" returns the size of the data fork, not the
total size of data fork plus resource fork.
(Mac OS).
"-s" by name on an open file will return the space
reserved on disk, rather than the current extent.
"-s" on an open filehandle returns the current
size. (RISC OS)
"-R", "-W", "-X", "-O" are indistinguishable from
"-r", "-w", "-x", "-o". (Mac OS, Win32, VMS,
RISC OS)
"-b", "-c", "-k", "-g", "-p", "-u", "-A" are not
implemented. (Mac OS)
"-g", "-k", "-l", "-p", "-u", "-A" are not partic-
ularly 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 misclas-
sify 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 exe-
cutable 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 sys-
tem Perl is run on does not allow it. (Tru64, HP-
UX 10.20)
The current version of the standards for "atan2()"
is available at .
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 sys-
tem Perl is run on does not allow it. (Tru64, HP-
UX 10.20)
The current version of the standards for "atan2()"
is available at .
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-con-
trol list changes. (VOS)
The actual permissions set depend on the value of
the "CYGWIN" in the SYSTEM environment settings.
(Cygwin)
chown Not implemented. (Mac OS, Win32, Plan 9, RISC OS,
VOS)
Does nothing, but won't fail. (Win32)
chroot Not implemented. (Mac OS, Win32, VMS, Plan 9,
RISC OS, VOS, VM/ESA)
crypt May not be available if library or source was not
provided when building perl. (Win32)
Not implemented. (VOS)
dbmclose
Not implemented. (VMS, Plan 9, VOS)
dbmopen Not implemented. (VMS, Plan 9, VOS)
dump Not useful. (Mac OS, RISC OS)
Not implemented. (Win32)
Invokes VMS debugger. (VMS)
exec Not implemented. (Mac OS)
Implemented via Spawn. (VM/ESA)
Does not automatically flush output handles on
some platforms. (SunOS, Solaris, HP-UX)
exit Emulates UNIX exit() (which considers "exit 1" to
indicate an error) by mapping the 1 to SS$_ABORT
(44). This behavior may be overridden with the
pragma "use vmsish 'exit'". As with the CRTL's
exit() function, "exit 0" is also mapped to an
exit status of SS$_NORMAL (1); this mapping cannot
be overridden. Any other argument to exit() is
used directly as Perl's exit status. (VMS)
fcntl Not implemented. (Win32, VMS)
flock Not implemented (Mac OS, VMS, RISC OS, VOS).
Available only on Windows NT (not on Windows 95).
(Win32)
fork Not implemented. (Mac OS, AmigaOS, RISC OS, VOS,
VM/ESA, VMS)
Emulated using multiple interpreters. See perl-
fork. (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 every-
where: you may have to use "gethostby-
name('127.0.0.1')". (Mac OS, Irix 5)
gethostent
Not implemented. (Mac OS, Win32)
getnetent
Not implemented. (Mac OS, Win32, Plan 9)
getprotoent
Not implemented. (Mac OS, Win32, Plan 9)
getservent
Not implemented. (Win32, Plan 9)
sethostent
Not implemented. (Mac OS, Win32, Plan 9, RISC OS)
setnetent
Not implemented. (Mac OS, Win32, Plan 9, RISC OS)
setprotoent
Not implemented. (Mac OS, Win32, Plan 9, RISC OS)
setservent
Not implemented. (Plan 9, Win32, RISC OS)
endpwent
Not implemented. (Mac OS, MPE/iX, VM/ESA, Win32)
endgrent
Not implemented. (Mac OS, MPE/iX, RISC OS, VM/ESA,
VMS, Win32)
endhostent
Not implemented. (Mac OS, Win32)
endnetent
Not implemented. (Mac OS, Win32, Plan 9)
endprotoent
Not implemented. (Mac OS, Win32, Plan 9)
endservent
Not implemented. (Plan 9, Win32)
getsockopt SOCKET,LEVEL,OPTNAME
Not implemented. (Plan 9)
glob This operator is implemented via the File::Glob
extension on most platforms. See File::Glob for
portability information.
gmtime Same portability caveats as localtime.
ioctl FILEHANDLE,FUNCTION,SCALAR
Not implemented. (VMS)
Available only for socket handles, and it does
what the ioctlsocket() call in the Winsock API
does. (Win32)
Available only for socket handles. (RISC OS)
kill "kill(0, LIST)" is implemented for the sake of
taint checking; use with other signals is unimple-
mented. (Mac OS)
Not implemented, hence not useful for taint check-
ing. (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 identi-
fied 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 stan-
dard 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 implementa-
tion 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 dif-
ferent logical volumes. (Win32)
select Only implemented on sockets. (Win32, VMS)
Only reliable on sockets. (RISC OS)
Note that the "select FILEHANDLE" form is gener-
ally 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 compar-
ison 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 modifi-
cation time. Device and inode are not necessarily
reliable. (RISC OS)
dev, rdev, blksize, and blocks are not available.
inode is not meaningful and will differ between
stat calls on the same file. (os2)
some versions of cygwin when doing a stat("foo")
and if not finding it may then attempt to
stat("foo.exe") (Cygwin)
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 imple-
mented with different numeric values on some sys-
tems. 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 "$? & 128" would test true if the program
was terminated by a coredump. Instead, use the
POSIX W*() interfaces: for example, use WIFEX-
ITED($?) and WEXITVALUE($?) to test for a normal
exit and the exit value, WIFSIGNALED($?) and
WTERMSIG($?) for a signal exit and the signal.
Core dumping is not a portable concept, so there's
no portable way to test for that.
Only implemented if ToolServer is installed.
(Mac OS)
As an optimization, may not call the command shell
specified in $ENV{PERL5SHELL}. "system(1, @args)"
spawns an external process and immediately returns
its process designator, without waiting for it to
terminate. Return value may be used subsequently
in "wait" or "waitpid". Failure to spawn() a sub-
process 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 ter-
minated by "\n" "\r" or "\0" to the spawned pro-
gram. Redirection such as "> foo" is performed
(if at all) by the run time library of the spawned
program. "system" list will call the Unix emula-
tion library's "exec" emulation, which attempts to
provide emulation of the stdin, stdout, stderr in
force in the parent, providing the child program
uses a compatible version of the emulation
library. scalar will call the native command line
direct and no such emulation of a child Unix pro-
gram 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,
'>>filename')" or
"sysopen(FH,...,O_APPEND|O_RDWR)". If a filename
is supplied, it should not be held open elsewhere.
(Win32)
umask Returns undef where unavailable, as of version
5.005.
"umask" works but the correct permissions are set
only when the file is finally closed. (AmigaOS)
utime Only the modification time is updated. (BeOS,
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 follow-
ing 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 plat-
forms--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 distri-
butions 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 distribu-
tions.
SEE ALSO
perlaix, perlamiga, perlapollo, perlbeos, perlbs2000,
perlce, perlcygwin, perldgux, perldos, perlepoc,
perlebcdic, perlfreebsd, perlhurd, perlhpux, perlirix,
perlmachten, perlmacos, perlmacosx, perlmint, perlmpeix,
perlnetware, perlos2, perlos390, perlos400, perlplan9,
perlqnx, perlsolaris, perltru64, perlunicode, perlvmesa,
perlvms, perlvos, perlwin32, and Win32.
AUTHORS / CONTRIBUTORS
Abigail , Charles Bailey , Graham Barr , Tom Chris-
tiansen , Nicholas Clark
, Thomas Dorner ,
Andy Dougherty , Dominic Dunlop
, Neale Ferguson , David J. Fiander , Paul Green
, M.J.T. Guy ,
Jarkko Hietaniemi , Luther Huffman
, Nick Ing-Simmons , Andreas J. Koenig , Markus
Laker , Andrew M. Langmead
, Larry Moore ,
Paul Moore , Chris Nandor
, Matthias Neeracher ,
Philip Newton , Gary Ng <71564.1743@Com-
puServe.COM>, Tom Phoenix , Andre
Pirard , Peter Prymmer
, Hugo van der Sanden
, Gurusamy Sarathy , Paul J. Schinder , Michael
G Schwern , Dan Sugalski
, Nathan Torkington .
perl v5.8.8 2006-01-07 PERLPORT(1)