NAME¶
perlport - Writing portable Perl
DESCRIPTION¶
Perl runs on numerous operating systems. While most of them share much in
common, they also have their own unique features.
This document is meant to help you to find out what constitutes portable Perl
code. That way once you make a decision to write portably, you know where the
lines are drawn, and you can stay within them.
There is a tradeoff between taking full advantage of one particular type of
computer and taking advantage of a full range of them. Naturally, as you
broaden your range and become more diverse, the common factors drop, and you
are left with an increasingly smaller area of common ground in which you can
operate to accomplish a particular task. Thus, when you begin attacking a
problem, it is important to consider under which part of the tradeoff curve
you want to operate. Specifically, you must decide whether it is important
that the task that you are coding have the full generality of being portable,
or whether to just get the job done right now. This is the hardest choice to
be made. The rest is easy, because Perl provides many choices, whichever way
you want to approach your problem.
Looking at it another way, writing portable code is usually about willfully
limiting your available choices. Naturally, it takes discipline and sacrifice
to do that. The product of portability and convenience may be a constant. You
have been warned.
Be aware of two important points:
- 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 Macintosh application, or to manage the
Windows registry. If it makes no sense to aim for portability for one
reason or another in a given program, then don't bother.
- Nearly all of Perl already is portable
- Don't be fooled into thinking that it is hard to create portable Perl
code. It isn't. Perl tries its level-best to bridge the gaps between
what's available on different platforms, and all the means available to
use those features. Thus almost all Perl code runs on any machine without
modification. But there are some significant issues in writing portable
code, and this document is entirely about those issues.
Here's the general rule: When you approach a task commonly done using a whole
range of platforms, think about writing portable code. That way, you don't
sacrifice much by way of the implementation choices you can avail yourself of,
and at the same time you can give your users lots of platform choices. On the
other hand, when you have to take advantage of some unique feature of a
particular platform, as is often the case with systems programming (whether
for Unix, Windows, VMS, etc.), consider writing platform-specific code.
When the code will run on only two or three operating systems, you may need to
consider only the differences of those particular systems. The important thing
is to decide where the code will run and to be deliberate in your decision.
The material below is separated into three main sections: main issues of
portability ("ISSUES"), platform-specific issues
("PLATFORMS"), and built-in perl functions that behave differently
on various ports ("FUNCTION IMPLEMENTATIONS").
This information should not be considered complete; it includes possibly
transient information about idiosyncrasies of some of the ports, almost all of
which are in a state of constant evolution. Thus, this material should be
considered a perpetual work in progress ("<IMG
SRC="yellow_sign.gif" ALT="Under Construction">").
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, perl
uses the ":crlf" layer that translates it to (or from)
"\015\012", depending on whether you're reading or writing. Unix
does the same thing on ttys in canonical mode. "\015\012" is
commonly referred to as CRLF.
To trim trailing newlines from text lines use
chomp(). With default
settings that function looks for a trailing "\n" character and thus
trims in a portable way.
When dealing with binary files (or text files in binary mode) be sure to
explicitly set $/ to the appropriate value for your file format before using
chomp().
Because of the "text" mode translation, DOSish perls have limitations
in using "seek" and "tell" on a file accessed in
"text" mode. Stick to "seek"-ing to locations you got from
"tell" (and no others), and you are usually free to use
"seek" and "tell" even in "text" mode. Using
"seek" or "tell" or other file operations may be
non-portable. If you use "binmode" on a file, however, you can
usually "seek" and "tell" with arbitrary values in safety.
A common misconception in socket programming is that "\n" eq
"\012" everywhere. When using protocols such as common Internet
protocols, "\012" and "\015" are called for specifically,
and the values of the logical "\n" and "\r" (carriage
return) are not reliable.
print SOCKET "Hi there, client!\r\n"; # WRONG
print SOCKET "Hi there, client!\015\012"; # RIGHT
However, using "\015\012" (or "\cM\cJ", or
"\x0D\x0A") can be tedious and unsightly, as well as confusing to
those maintaining the code. As such, the Socket module supplies the Right
Thing for those who want it.
use Socket qw(:DEFAULT :crlf);
print SOCKET "Hi there, client!$CRLF" # RIGHT
When reading from a socket, remember that the default input record separator $/
is "\n", but robust socket code will recognize as either
"\012" or "\015\012" as end of line:
while (<SOCKET>) {
# ...
}
Because both CRLF and LF end in LF, the input record separator can be set to LF
and any CR stripped later. Better to write:
use Socket qw(:DEFAULT :crlf);
local($/) = LF; # not needed if $/ is already \012
while (<SOCKET>) {
s/$CR?$LF/\n/; # not sure if socket uses LF or CRLF, OK
# s/\015?\012/\n/; # same thing
}
This example is preferred over the previous one--even for Unix
platforms--because now any "\015"'s ("\cM"'s) are stripped
out (and there was much rejoicing).
Similarly, functions that return text data--such as a function that fetches a
web page--should sometimes translate newlines before returning the data, if
they've not yet been translated to the local newline representation. A single
line of code will often suffice:
$data =~ s/\015?\012/\n/g;
return $data;
Some of this may be confusing. Here's a handy reference to the ASCII CR and LF
characters. You can print it out and stick it in your wallet.
LF eq \012 eq \x0A eq \cJ eq chr(10) eq ASCII 10
CR eq \015 eq \x0D eq \cM eq chr(13) eq ASCII 13
| Unix | DOS | Mac |
---------------------------
\n | LF | LF | CR |
\r | CR | CR | LF |
\n * | LF | CRLF | CR |
\r * | CR | CR | LF |
---------------------------
* text-mode STDIO
The Unix column assumes that you are not accessing a serial line (like a tty) in
canonical mode. If you are, then CR on input becomes "\n", and
"\n" on output becomes CRLF.
These are just the most common definitions of "\n" and "\r"
in Perl. There may well be others. For example, on an EBCDIC implementation
such as z/OS (OS/390) or OS/400 (using the ILE, the PASE is ASCII-based) the
above material is similar to "Unix" but the code numbers change:
LF eq \025 eq \x15 eq \cU eq chr(21) eq CP-1047 21
LF eq \045 eq \x25 eq chr(37) eq CP-0037 37
CR eq \015 eq \x0D eq \cM eq chr(13) eq CP-1047 13
CR eq \015 eq \x0D eq \cM eq chr(13) eq CP-0037 13
| z/OS | OS/400 |
----------------------
\n | LF | LF |
\r | CR | CR |
\n * | LF | LF |
\r * | CR | CR |
----------------------
* text-mode STDIO
Numbers endianness and Width¶
Different CPUs store integers and floating point numbers in different orders
(called
endianness) and widths (32-bit and 64-bit being the most common
today). This affects your programs when they attempt to transfer numbers in
binary format from one CPU architecture to another, usually either
"live" via network connection, or by storing the numbers to
secondary storage such as a disk file or tape.
Conflicting storage orders make utter mess out of the numbers. If a
little-endian host (Intel, VAX) stores 0x12345678 (305419896 in decimal), a
big-endian host (Motorola, Sparc, PA) reads it as 0x78563412 (2018915346 in
decimal). Alpha and MIPS can be either: Digital/Compaq used/uses them in
little-endian mode; SGI/Cray uses them in big-endian mode. To avoid this
problem in network (socket) connections use the "pack" and
"unpack" formats "n" and "N", the
"network" orders. These are guaranteed to be portable.
As of perl 5.10.0, you can also use the ">" and "<"
modifiers to force big- or little-endian byte-order. This is useful if you
want to store signed integers or 64-bit integers, for example.
You can explore the endianness of your platform by unpacking a data structure
packed in native format such as:
print unpack("h*", pack("s2", 1, 2)), "\n";
# '10002000' on e.g. Intel x86 or Alpha 21064 in little-endian mode
# '00100020' on e.g. Motorola 68040
If you need to distinguish between endian architectures you could use either of
the variables set like so:
$is_big_endian = unpack("h*", pack("s", 1)) =~ /01/;
$is_little_endian = unpack("h*", pack("s", 1)) =~ /^1/;
Differing widths can cause truncation even between platforms of equal
endianness. The platform of shorter width loses the upper parts of the number.
There is no good solution for this problem except to avoid transferring or
storing raw binary numbers.
One can circumnavigate both these problems in two ways. Either transfer and
store numbers always in text format, instead of raw binary, or else consider
using modules like Data::Dumper and Storable (included as of perl 5.8).
Keeping all data as text significantly simplifies matters.
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 idiosyncratic ways (such as having several
root directories and various "unrooted" device files such NIL: and
LPT:).
Mac OS 9 and earlier used ":" as a path separator instead of
"/".
The filesystem may support neither hard links ("link") nor symbolic
links ("symlink", "readlink", "lstat").
The filesystem may support neither access timestamp nor change timestamp
(meaning that about the only portable timestamp is the modification
timestamp), or one second granularity of any timestamps (e.g. the FAT
filesystem limits the time granularity to two seconds).
The "inode change timestamp" (the "-C" filetest) may really
be the "creation timestamp" (which it is not in Unix).
VOS perl can emulate Unix filenames with "/" as path separator. The
native pathname characters greater-than, less-than, number-sign, and
percent-sign are always accepted.
RISC OS perl can emulate Unix filenames with "/" as path
separator, or go native and use "." for path separator and
":" to signal filesystems and disk names.
Don't assume Unix filesystem access semantics: that read, write, and execute are
all the permissions there are, and even if they exist, that their semantics
(for example what do r, w, and x mean on a directory) are the Unix ones. The
various Unix/POSIX compatibility layers usually try to make interfaces like
chmod() work, but sometimes there simply is no good mapping.
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
my $file = catfile(curdir(), 'temp', 'file.txt');
# on Unix and Win32, './temp/file.txt'
# on Mac OS Classic, ':temp:file.txt'
# on VMS, '[.temp]file.txt'
File::Spec is available in the standard distribution as of version 5.004_05.
File::Spec::Functions is only in File::Spec 0.7 and later, and some versions
of perl come with version 0.6. If File::Spec is not updated to 0.7 or later,
you must use the object-oriented interface from File::Spec (or upgrade
File::Spec).
In general, production code should not have file paths hardcoded. Making them
user-supplied or read from a configuration file is better, keeping in mind
that file path syntax varies on different machines.
This is especially noticeable in scripts like Makefiles and test suites, which
often assume "/" as a path separator for subdirectories.
Also of use is File::Basename from the standard distribution, which splits a
pathname into pieces (base filename, full path to directory, and file suffix).
Even when on a single platform (if you can call Unix a single platform),
remember not to count on the existence or the contents of particular
system-specific files or directories, like
/etc/passwd,
/etc/sendmail.conf,
/etc/resolv.conf, or even
/tmp/. For
example,
/etc/passwd may exist but not contain the encrypted passwords,
because the system is using some form of enhanced security. Or it may not
contain all the accounts, because the system is using NIS. If code does need
to rely on such a file, include a description of the file and its format in
the code's documentation, then make it easy for the user to override the
default location of the file.
Don't assume a text file will end with a newline. They should, but people
forget.
Do not have two files or directories of the same name with different case, like
test.pl and
Test.pl, as many platforms have case-insensitive (or
at least case-forgiving) filenames. Also, try not to have non-word characters
(except for ".") in the names, and keep them to the 8.3 convention,
for maximum portability, onerous a burden though this may appear.
Likewise, when using the AutoSplit module, try to keep your functions to 8.3
naming and case-insensitive conventions; or, at the least, make it so the
resulting files have a unique (case-insensitively) first 8 characters.
Whitespace in filenames is tolerated on most systems, but not all, and even on
systems where it might be tolerated, some utilities might become confused by
such whitespace.
Many systems (DOS, VMS ODS-2) cannot have more than one "." in their
filenames.
Don't assume ">" won't be the first character of a filename. Always
use "<" explicitly to open a file for reading, or even better,
use the three-arg version of open, unless you want the user to be able to
specify a pipe open.
open my $fh, '<', $existing_file) or die $!;
If filenames might use strange characters, it is safest to open it with
"sysopen" instead of "open". "open" is magic and
can translate characters like ">", "<", and
"|", which may be the wrong thing to do. (Sometimes, though, it's
the right thing.) Three-arg open can also help protect against this
translation in cases where it is undesirable.
Don't use ":" as a part of a filename since many systems use that for
their own semantics (Mac OS Classic for separating pathname components, many
networking schemes and utilities for separating the nodename and the pathname,
and so on). For the same reasons, avoid "@", ";" and
"|".
Don't assume that in pathnames you can collapse two leading slashes
"//" into one: some networking and clustering filesystems have
special semantics for that. Let the operating system to sort it out.
The
portable filename characters as defined by ANSI C are
a b c d e f g h i j k l m n o p q r t u v w x y z
A B C D E F G H I J K L M N O P Q R T U V W X Y Z
0 1 2 3 4 5 6 7 8 9
. _ -
and the "-" shouldn't be the first character. If you want to be
hypercorrect, stay case-insensitive and within the 8.3 naming convention (all
the files and directories have to be unique within one directory if their
names are lowercased and truncated to eight characters before the
".", if any, and to three characters after the ".", if
any). (And do not use "."s in directory names.)
System Interaction¶
Not all platforms provide a command line. These are usually platforms that rely
primarily on a Graphical User Interface (GUI) for user interaction. A program
requiring a command line interface might not work everywhere. This is probably
for the user of the program to deal with, so don't stay up late worrying about
it.
Some platforms can't delete or rename files held open by the system, this
limitation may also apply to changing filesystem metainformation like file
permissions or owners. Remember to "close" files when you are done
with them. Don't "unlink" or "rename" an open file. Don't
"tie" or "open" a file already tied or opened;
"untie" or "close" it first.
Don't open the same file more than once at a time for writing, as some operating
systems put mandatory locks on such files.
Don't assume that write/modify permission on a directory gives the right to add
or delete files/directories in that directory. That is filesystem specific: in
some filesystems you need write/modify permission also (or even just) in the
file/directory itself. In some filesystems (AFS, DFS) the permission to
add/delete directory entries is a completely separate permission.
Don't assume that a single "unlink" completely gets rid of the file:
some filesystems (most notably the ones in VMS) have versioned filesystems,
and
unlink() removes only the most recent one (it doesn't remove all
the versions because by default the native tools on those platforms remove
just the most recent version, too). The portable idiom to remove all the
versions of a file is
1 while unlink "file";
This will terminate if the file is undeleteable for some reason (protected, not
there, and so on).
Don't count on a specific environment variable existing in %ENV. Don't count on
%ENV entries being case-sensitive, or even case-preserving. Don't try to clear
%ENV by saying "%ENV = ();", or, if you really have to, make it
conditional on "$^O ne 'VMS'" since in VMS the %ENV table is much
more than a per-process key-value string table.
On VMS, some entries in the %ENV hash are dynamically created when their key is
used on a read if they did not previously exist. The values for $ENV{HOME},
$ENV{TERM}, $ENV{HOME}, and $ENV{USER}, are known to be dynamically generated.
The specific names that are dynamically generated may vary with the version of
the C library on VMS, and more may exist than is documented.
On VMS by default, changes to the %ENV hash are persistent after the process
exits. This can cause unintended issues.
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 suffixes for executable files; these suffixes are
generally permitted on the command name but are not required. Thus, a command
like "perl" might exist in a file named "perl",
"perl.exe", or "perl.pm", depending on the operating
system. The variable "_exe" in the Config module holds the
executable suffix, if any. Third, the VMS port carefully sets up $^X and
$Config{perlpath} so that no further processing is required. This is just as
well, because the matching regular expression used below would then have to
deal with a possible trailing version number in the VMS file name.
To convert $^X to a file pathname, taking account of the requirements of the
various operating system possibilities, say:
use Config;
my $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;
my $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 that for things such as 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 different arguments, can behave differently,
and often present their results in a platform-dependent way. Thus, you should
seldom depend on them to produce consistent results. (Then again, if you're
calling
netstat -a, you probably don't expect it to run on both Unix
and CP/M.)
One especially common bit of Perl code is opening a pipe to
sendmail:
open(MAIL, '|/usr/lib/sendmail -t')
or die "cannot fork sendmail: $!";
This is fine for systems programming when sendmail is known to be available. But
it is not fine for many non-Unix systems, and even some Unix systems that may
not have sendmail installed. If a portable solution is needed, see the various
distributions on CPAN that deal with it. Mail::Mailer and Mail::Send in the
MailTools distribution are commonly used, and provide several mailing methods,
including mail, sendmail, and direct SMTP (via Net::SMTP) if a mail transfer
agent is not available. Mail::Sendmail is a standalone module that provides
simple, platform-independent mailing.
The Unix System V IPC ("msg*(), sem*(), shm*()") is not available even
on all Unix platforms.
Do not use either the bare result of "pack("N", 10, 20, 30,
40)" or bare v-strings (such as "v10.20.30.40") to represent
IPv4 addresses: both forms just pack the four bytes into network order. That
this would be equal to the C language "in_addr" struct (which is
what the socket code internally uses) is not guaranteed. To be portable use
the routines of the Socket extension, such as "inet_aton()",
"inet_ntoa()", and "sockaddr_in()".
The rule of thumb for portable code is: Do it all in portable Perl, or use a
module (that may internally implement it with platform-specific code, but
expose a common interface).
External Subroutines (XS)¶
XS code can usually be made to work with any platform, but dependent libraries,
header files, etc., might not be readily available or portable, or the XS code
itself might be platform-specific, just as Perl code might be. If the
libraries and headers are portable, then it is normally reasonable to make
sure the XS code is portable, too.
A different type of portability issue arises when writing XS code: availability
of a C compiler on the end-user's system. C brings with it its own portability
issues, and writing XS code will expose you to some of those. Writing purely
in Perl is an easier way to achieve portability.
Standard Modules¶
In general, the standard modules work across platforms. Notable exceptions are
the CPAN module (which currently makes connections to external programs that
may not be available), platform-specific modules (like ExtUtils::MM_VMS), and
DBM modules.
There is no one DBM module available on all platforms. SDBM_File and the others
are generally 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 guess
what date 02/03/04 might be. ISO 8601 even sorts nicely as-is. A text
representation (like "1987-12-18") can be easily converted into an
OS-specific value using a module like Date::Parse. An array of values, such as
those returned by "localtime", can be converted to an OS-specific
representation using Time::Local.
When calculating specific times, such as for tests in time or date modules, it
may be appropriate to calculate an offset for the epoch.
require Time::Local;
my $offset = Time::Local::timegm(0, 0, 0, 1, 0, 70);
The value for $offset in Unix will be 0, but in Mac OS Classic will be some
large number. $offset can then be added to a Unix time value to get what
should be the proper value on any system.
Character sets and character encoding¶
Assume very little about character sets.
Assume nothing about numerical values ("ord", "chr") of
characters. Do not use explicit code point ranges (like \xHH-\xHH); use for
example symbolic character classes like "[:print:]".
Do not assume that the alphabetic characters are encoded contiguously (in the
numeric sense). There may be gaps.
Do not assume anything about the ordering of the characters. The lowercase
letters may come before or after the uppercase letters; the lowercase and
uppercase may be interlaced so that both "a" and "A" come
before "b"; the accented and other international characters may be
interlaced so that ae comes before "b".
Internationalisation¶
If you may assume POSIX (a rather large assumption), you may read more about the
POSIX locale system from perllocale. The locale system at least attempts to
make things a little bit more portable, or at least more convenient and
native-friendly for non-English users. The system affects character sets and
encoding, and date and time formatting--amongst other things.
If you really want to be international, you should consider Unicode. See
perluniintro and 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 you want to write your code in UTF-8, you can use the
"utf8".
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:
my @lines = <$very_large_file>; # bad
while (<$fh>) {$file .= $_} # sometimes bad
my $file = join('', <$fh>); # better
The last two constructs may appear unintuitive to most people. The first
repeatedly grows a string, whereas the second allocates a large chunk of
memory in one go. On some systems, the second is more efficient that the
first.
Security¶
Most multi-user platforms provide basic levels of security, usually implemented
at the filesystem level. Some, however, unfortunately do not. Thus the notion
of user id, or "home" directory, or even the state of being
logged-in, may be unrecognizable on many platforms. If you write programs that
are security-conscious, it is usually best to know what type of system you
will be running under so that you can write code explicitly for that platform
(or class of platforms).
Don't assume the Unix filesystem access semantics: the operating system or the
filesystem may be using some ACL systems, which are richer languages than the
usual rwx. Even if the rwx exist, their semantics might be different.
(From security viewpoint testing for permissions before attempting to do
something is silly anyway: if one tries this, there is potential for race
conditions. Someone or something might change the permissions between the
permissions check and the actual operation. Just try the operation.)
Don't assume the Unix user and group semantics: especially, don't expect the
$< and $> (or the $( and $)) to work for switching identities (or
memberships).
Don't assume set-uid and set-gid semantics. (And even if you do, think twice:
set-uid and set-gid are a known can of security worms.)
Style¶
For those times when it is necessary to have platform-specific code, consider
keeping the platform-specific 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 module works on a
given platform.
Also see:
- •
- Mailing list: cpan-testers-discuss@perl.org
- •
- Testing results: <http://www.cpantesters.org/>
Perl is built with a $^O variable that indicates the operating system it was
built on. This was implemented to help speed up code that would otherwise have
to "use Config" and use the value of $Config{osname}. Of course, to
get more detailed information about the system, looking into %Config is
certainly recommended.
%Config cannot always be trusted, however, because it was built at compile time.
If perl was built in one place, then transferred elsewhere, some values may be
wrong. The values may even have been edited after the fact.
Unix¶
Perl works on a bewildering variety of Unix and Unix-like platforms (see e.g.
most of the files in the
hints/ directory in the source code kit). On
most of these systems, the value of $^O (hence $Config{'osname'}, too) is
determined either by lowercasing and stripping punctuation from the first
field of the string returned by typing "uname -a" (or a similar
command) at the shell prompt or by testing the file system for the presence of
uniquely named files such as a kernel or header file. Here, for example, are a
few of the more popular Unix flavors:
uname $^O $Config{'archname'}
--------------------------------------------
AIX aix aix
BSD/OS bsdos i386-bsdos
Darwin darwin darwin
DYNIX/ptx dynixptx i386-dynixptx
FreeBSD freebsd freebsd-i386
Haiku haiku BePC-haiku
Linux linux arm-linux
Linux linux armv5tel-linux
Linux linux i386-linux
Linux linux i586-linux
Linux linux ppc-linux
HP-UX hpux PA-RISC1.1
IRIX irix irix
Mac OS X darwin darwin
NeXT 3 next next-fat
NeXT 4 next OPENSTEP-Mach
openbsd openbsd i386-openbsd
OSF1 dec_osf alpha-dec_osf
reliantunix-n svr4 RM400-svr4
SCO_SV sco_sv i386-sco_sv
SINIX-N svr4 RM400-svr4
sn4609 unicos CRAY_C90-unicos
sn6521 unicosmk t3e-unicosmk
sn9617 unicos CRAY_J90-unicos
SunOS solaris sun4-solaris
SunOS solaris i86pc-solaris
SunOS4 sunos sun4-sunos
Because the value of $Config{archname} 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:
my $filespec0 = "c:/foo/bar/file.txt";
my $filespec1 = "c:\\foo\\bar\\file.txt";
my $filespec2 = 'c:\foo\bar\file.txt';
my $filespec3 = 'c:\\foo\\bar\\file.txt';
System calls accept either "/" or "\" as the path separator.
However, many command-line utilities of DOS vintage treat "/" as the
option prefix, so may get confused by filenames containing "/".
Aside from calling any external programs, "/" will work just fine,
and probably better, as it is more consistent with popular usage, and avoids
the problem of remembering what to backwhack and what not to.
The DOS FAT filesystem can accommodate only "8.3" style filenames.
Under the "case-insensitive, but case-preserving" HPFS (OS/2) and
NTFS (NT) filesystems you may have to be careful about case returned with
functions like "readdir" or used with functions like
"open" or "opendir".
DOS also treats several filenames as special, such as AUX, PRN, NUL, CON, COM1,
LPT1, LPT2, etc. Unfortunately, sometimes these filenames won't even work if
you include an explicit directory prefix. It is best to avoid such filenames,
if you want your code to be portable to DOS and its derivatives. It's hard to
know what these all are, unfortunately.
Users of these operating systems may also wish to make use of scripts such as
pl2bat.bat or
pl2cmd to put wrappers around your scripts.
Newline ("\n") is translated as "\015\012" by STDIO when
reading from and writing to files (see "Newlines").
"binmode(FILEHANDLE)" will keep "\n" translated as
"\012" for that filehandle. Since it is a no-op on other systems,
"binmode" should be used for cross-platform code that deals with
binary data. That's assuming you realize in advance that your data is in
binary. General-purpose programs should often assume nothing about their data.
The $^O variable and the $Config{archname} values for various DOSish perls are
as follows:
OS $^O $Config{archname} ID Version
--------------------------------------------------------
MS-DOS dos ?
PC-DOS dos ?
OS/2 os2 ?
Windows 3.1 ? ? 0 3 01
Windows 95 MSWin32 MSWin32-x86 1 4 00
Windows 98 MSWin32 MSWin32-x86 1 4 10
Windows ME MSWin32 MSWin32-x86 1 ?
Windows NT MSWin32 MSWin32-x86 2 4 xx
Windows NT MSWin32 MSWin32-ALPHA 2 4 xx
Windows NT MSWin32 MSWin32-ppc 2 4 xx
Windows 2000 MSWin32 MSWin32-x86 2 5 00
Windows XP MSWin32 MSWin32-x86 2 5 01
Windows 2003 MSWin32 MSWin32-x86 2 5 02
Windows Vista MSWin32 MSWin32-x86 2 6 00
Windows 7 MSWin32 MSWin32-x86 2 6 01
Windows 7 MSWin32 MSWin32-x64 2 6 01
Windows 2008 MSWin32 MSWin32-x86 2 6 01
Windows 2008 MSWin32 MSWin32-x64 2 6 01
Windows CE MSWin32 ? 3
Cygwin cygwin cygwin
The various MSWin32 Perl's can distinguish the OS they are running on via the
value of the fifth element of the list returned from
Win32::GetOSVersion(). For example:
if ($^O eq 'MSWin32') {
my @os_version_info = Win32::GetOSVersion();
print +('3.1','95','NT')[$os_version_info[4]],"\n";
}
There are also
Win32::IsWinNT() 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,
<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
VMS¶
Perl on VMS is discussed in perlvms in the perl distribution.
The official name of VMS as of this writing is OpenVMS.
Perl on VMS can accept either VMS- or Unix-style file specifications as in
either of the following:
$ perl -ne "print if /perl_setup/i" SYS$LOGIN:LOGIN.COM
$ perl -ne "print if /perl_setup/i" /sys$login/login.com
but not a mixture of both as in:
$ perl -ne "print if /perl_setup/i" sys$login:/login.com
Can't open sys$login:/login.com: file specification syntax error
Interacting with Perl from the Digital Command Language (DCL) shell often
requires a different set of quotation marks than Unix shells do. For example:
$ perl -e "print ""Hello, world.\n"""
Hello, world.
There are several ways to wrap your perl scripts in DCL
.COM files, if
you are so inclined. For example:
$ write sys$output "Hello from DCL!"
$ if p1 .eqs. ""
$ then perl -x 'f$environment("PROCEDURE")
$ else perl -x - 'p1 'p2 'p3 'p4 'p5 'p6 'p7 'p8
$ deck/dollars="__END__"
#!/usr/bin/perl
print "Hello from Perl!\n";
__END__
$ endif
Do take care with "$ ASSIGN/nolog/user SYS$COMMAND: SYS$INPUT" if your
perl-in-DCL script expects to do things like "$read =
<STDIN>;".
The VMS operating system has two filesystems, known as ODS-2 and ODS-5.
For ODS-2, filenames are in the format "name.extension;version". The
maximum length for filenames is 39 characters, and the maximum length for
extensions is also 39 characters. Version is a number from 1 to 32767. Valid
characters are "/[A-Z0-9$_-]/".
The ODS-2 filesystem is case-insensitive and does not preserve case. Perl
simulates this by converting all filenames to lowercase internally.
For ODS-5, filenames may have almost any character in them and can include
Unicode characters. Characters that could be misinterpreted by the DCL shell
or file parsing utilities need to be prefixed with the "^"
character, or replaced with hexadecimal characters prefixed with the
"^" character. Such prefixing is only needed with the pathnames are
in VMS format in applications. Programs that can accept the Unix format of
pathnames do not need the escape characters. The maximum length for filenames
is 255 characters. The ODS-5 file system can handle both a case preserved and
a case sensitive mode.
ODS-5 is only available on the OpenVMS for 64 bit platforms.
Support for the extended file specifications is being done as optional settings
to preserve backward compatibility with Perl scripts that assume the previous
VMS limitations.
In general routines on VMS that get a Unix format file specification should
return it in a Unix format, and when they get a VMS format specification they
should return a VMS format unless they are documented to do a conversion.
For routines that generate return a file specification, VMS allows setting if
the C library which Perl is built on if it will be returned in VMS format or
in Unix format.
With the ODS-2 file system, there is not much difference in syntax of filenames
without paths for VMS or Unix. With the extended character set available with
ODS-5 there can be a significant difference.
Because of this, existing Perl scripts written for VMS were sometimes treating
VMS and Unix filenames interchangeably. Without the extended character set
enabled, this behavior will mostly be maintained for backwards compatibility.
When extended characters are enabled with ODS-5, the handling of Unix formatted
file specifications is to that of a Unix system.
VMS file specifications without extensions have a trailing dot. An equivalent
Unix file specification should not show the trailing dot.
The result of all of this, is that for VMS, for portable scripts, you can not
depend on Perl to present the filenames in lowercase, to be case sensitive,
and that the filenames could be returned in either Unix or VMS format.
And if a routine returns a file specification, unless it is intended to convert
it, it should return it in the same format as it found it.
"readdir" by default has traditionally returned lowercased filenames.
When the ODS-5 support is enabled, it will return the exact case of the
filename on the disk.
Files without extensions have a trailing period on them, so doing a
"readdir" in the default mode with a file named
A.;5 will
return
a. when VMS is (though that file could be opened with
"open(FH, 'A')").
With support for extended file specifications and if "opendir" was
given a Unix format directory, a file named
A.;5 will return
a
and optionally in the exact case on the disk. When "opendir" is
given a VMS format directory, then "readdir" should return
a., and again with the optionally the exact case.
RMS had an eight level limit on directory depths from any rooted logical
(allowing 16 levels overall) prior to VMS 7.2, and even with versions of VMS
on VAX up through 7.3. 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/".
Pumpkings and module integrators can easily see whether files with too many
directory levels have snuck into the core by running the following in the
top-level source directory:
$ perl -ne "$_=~s/\s+.*//; print if scalar(split /\//) > 8;" < MANIFEST
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. It is also
now the only way that you should check to see if VMS is in a case sensitive
mode.
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 TCP/IP library support for all current versions of VMS is dynamically loaded
if present, so even if the routines are configured, they may return a status
indicating that they are not implemented.
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";
} elsif (grep(/VMS_IA64/, @INC)) {
print "I'm on IA64!\n";
} else {
print "I'm not so sure about where $^O is...\n";
}
In general, the significant differences should only be if Perl is running on
VMS_VAX or one of the 64 bit OpenVMS platforms.
On VMS, perl determines the UTC offset from the
"SYS$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, vmsperl-subscribe@perl.org
- •
- vmsperl on the web, <http://www.sidhe.org/vmsperl/index.html>
VOS¶
Perl on VOS (also known as OpenVOS) is discussed in
README.vos in the
perl distribution (installed as perlvos). Perl on VOS can accept either VOS-
or Unix-style file specifications as in either of the following:
$ perl -ne "print if /perl_setup/i" >system>notices
$ perl -ne "print if /perl_setup/i" /system/notices
or even a mixture of both as in:
$ perl -ne "print if /perl_setup/i" >system/notices
Even though VOS allows the slash character to appear in object names, because
the VOS port of Perl interprets it as a pathname delimiting character, VOS
files, directories, or links whose names contain a slash character cannot be
processed. Such files must be renamed before they can be processed by Perl.
Older releases of VOS (prior to OpenVOS Release 17.0) limit file names to 32 or
fewer characters, prohibit file names from starting with a "-"
character, and prohibit file names from containing any character matching
"tr/ !#%&'()*;<=>?//".
Newer releases of VOS (OpenVOS Release 17.0 or later) support a feature known as
extended names. On these releases, file names can contain up to 255
characters, are prohibited from starting with a "-" character, and
the set of prohibited characters is reduced to any character matching
"tr/#%*<>?//". There are restrictions involving spaces and
apostrophes: these characters must not begin or end a name, nor can they
immediately precede or follow a period. Additionally, a space must not
immediately precede another space or hyphen. Specifically, the following
character combinations are prohibited: space-space, space-hyphen,
period-space, space-period, period-apostrophe, apostrophe-period, leading or
trailing space, and leading or trailing apostrophe. Although an extended file
name is limited to 255 characters, a path name is still limited to 256
characters.
The value of $^O on VOS is "vos". To determine the architecture that
you are running on without resorting to loading all of %Config you can examine
the content of the @INC array like so:
if ($^O =~ /vos/) {
print "I'm on a Stratus box!\n";
} else {
print "I'm not on a Stratus box!\n";
die;
}
Also see:
- •
- README.vos (installed as perlvos)
- •
- The VOS mailing list.
There is no specific mailing list for Perl on VOS. You can contact the
Stratus Technologies Customer Assistance Center (CAC) for your region, or
you can use the contact information located in the distribution files on
the Stratus Anonymous FTP site.
- •
- Stratus Technologies on the web at <http://www.stratus.com>
- •
- VOS Open-Source Software on the web at
<http://ftp.stratus.com/pub/vos/vos.html>
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 5.8.1/5.10.0 or
later to the PASE which is ASCII-based (as opposed to ILE which is
EBCDIC-based), see perlos400.
As of R2.5 of USS for OS/390 and Version 2.3 of VM/ESA these Unix sub-systems do
not support the "#!" shebang trick for script invocation. Hence, on
OS/390 and VM/ESA perl scripts can be executed with a header similar to the
following simple script:
: # use perl
eval 'exec /usr/local/bin/perl -S $0 ${1+"$@"}'
if 0;
#!/usr/local/bin/perl # just a comment really
print "Hello from perl!\n";
OS/390 will support the "#!" shebang trick in release 2.8 and beyond.
Calls to "system" and backticks can use POSIX shell syntax on all
S/390 systems.
On the AS/400, if PERL5 is in your library list, you may need to wrap your perl
scripts in a CL procedure to invoke them like so:
BEGIN
CALL PGM(PERL5/PERL) PARM('/QOpenSys/hello.pl')
ENDPGM
This will invoke the perl script
hello.pl in the root of the QOpenSys
file system. On the AS/400 calls to "system" or backticks must use
CL syntax.
On these platforms, bear in mind that the EBCDIC character set may have an
effect on what happens with some perl functions (such as "chr",
"pack", "print", "printf", "ord",
"sort", "sprintf", "unpack"), as well as
bit-fiddling with ASCII constants using operators like "^",
"&" and "|", not to mention dealing with socket
interfaces to ASCII computers (see "Newlines").
Fortunately, most web servers for the mainframe will correctly translate the
"\n" in the following statement to its ASCII equivalent
("\r" is the same under both Unix and OS/390):
print "Content-type: text/html\r\n\r\n";
The values of $^O on some of these platforms includes:
uname $^O $Config{'archname'}
--------------------------------------------
OS/390 os390 os390
OS400 os400 os400
POSIX-BC posix-bc BS2000-posix-bc
Some simple tricks for determining if you are running on an EBCDIC platform
could include any of the following (perhaps all):
if ("\t" eq "\005") { print "EBCDIC may be spoken here!\n"; }
if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; }
if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; }
One thing you may not want to rely on is the EBCDIC encoding of punctuation
characters since these may differ from code page to code page (and once your
module or script is rumoured to work with EBCDIC, folks will want it to work
with all EBCDIC character sets).
Also see:
- •
- perlos390, README.os390, perlbs2000, perlebcdic.
- •
- The perl-mvs@perl.org list is for discussion of porting issues as well as
general usage issues for all EBCDIC Perls. Send a message body of
"subscribe perl-mvs" to majordomo@perl.org.
- •
- AS/400 Perl information at <http://as400.rochester.ibm.com/> as well
as on CPAN in the ports/ directory.
Acorn RISC OS¶
Because Acorns use ASCII with newlines ("\n") in text files as
"\012" like Unix, and because Unix filename emulation is turned on
by default, most simple scripts will probably work "out of the box".
The native filesystem is modular, and individual filesystems are free to be
case-sensitive or insensitive, and are usually case-preserving. Some native
filesystems have name length limits, which file and directory names are
silently truncated to fit. Scripts should be aware that the standard
filesystem currently has a name length limit of
10 characters, with up
to 77 items in a directory, but other filesystems may not impose such
limitations.
Native filenames are of the form
Filesystem#Special_Field::DiskName.$.Directory.Directory.File
where
Special_Field is not usually present, but may contain . and $ .
Filesystem =~ m|[A-Za-z0-9_]|
DsicName =~ m|[A-Za-z0-9_/]|
$ represents the root directory
. is the path separator
@ is the current directory (per filesystem but machine global)
^ is the parent directory
Directory and File =~ m|[^\0- "\.\$\%\&:\@\\^\|\177]+|
The default filename translation is roughly "tr|/.|./|;"
Note that ""ADFS::HardDisk.$.File" ne
'ADFS::HardDisk.$.File'" and that the second stage of "$"
interpolation in regular expressions will fall foul of the $. if scripts are
not careful.
Logical paths specified by system variables containing comma-separated search
lists are also allowed; hence "System:Modules" is a valid filename,
and the filesystem will prefix "Modules" with each section of
"System$Path" until a name is made that points to an object on disk.
Writing to a new file "System:Modules" would be allowed only if
"System$Path" contains a single item list. The filesystem will also
expand system variables in filenames if enclosed in angle brackets, so
"<System$Dir>.Modules" would look for the file
"$ENV{'System$Dir'} . 'Modules'". The obvious
implication of this is that
fully qualified filenames can start with
"<>" and should be protected when
"open" is used for input.
Because "." was in use as a directory separator and filenames could
not be assumed to be unique after 10 characters, Acorn implemented the C
compiler to strip the trailing ".c" ".h" ".s"
and ".o" suffix from filenames specified in source code and store
the respective files in subdirectories named after the suffix. Hence files are
translated:
foo.h h.foo
C:foo.h C:h.foo (logical path variable)
sys/os.h sys.h.os (C compiler groks Unix-speak)
10charname.c c.10charname
10charname.o o.10charname
11charname_.c c.11charname (assuming filesystem truncates at 10)
The Unix emulation library's translation of filenames to native assumes that
this sort of translation is required, and it allows a user-defined list of
known suffixes that it will transpose in this fashion. This may seem
transparent, but consider that with these rules
foo/bar/baz.h and
foo/bar/h/baz both map to
foo.bar.h.baz, and that
"readdir" and "glob" cannot and do not attempt to emulate
the reverse mapping. Other "."'s in filenames are translated to
"/".
As implied above, the environment accessed through %ENV is global, and the
convention is that program specific environment variables are of the form
"Program$Name". Each filesystem maintains a current directory, and
the current filesystem's current directory is the
global current
directory. Consequently, sociable programs don't change the current directory
but rely on full pathnames, and programs (and Makefiles) cannot assume that
they can spawn a child process which can change the current directory without
affecting its parent (and everyone else for that matter).
Because native operating system filehandles are global and are currently
allocated down from 255, with 0 being a reserved value, the Unix emulation
library emulates Unix filehandles. Consequently, you can't rely on passing
"STDIN", "STDOUT", or "STDERR" to your children.
The desire of users to express filenames of the form
"<Foo$Dir>.Bar" on the command line unquoted causes problems,
too: "``" command output capture has to perform a guessing game. It
assumes that a string "<[^<>]+\$[^<>]>" is a
reference to an environment variable, whereas anything else involving
"<" or ">" is redirection, and generally manages to
be 99% right. Of course, the problem remains that scripts cannot rely on any
Unix tools being available, or that any tools found have Unix-like command
line arguments.
Extensions and XS are, in theory, buildable by anyone using free tools. In
practice, many don't, as users of the Acorn platform are used to binary
distributions. MakeMaker does run, but no available make currently copes with
MakeMaker's makefiles; even if and when this should be fixed, the lack of a
Unix-like shell will cause problems with makefile rules, especially lines of
the form "cd sdbm && make all", and anything using quoting.
"RISC OS" is the proper name for the operating system, but the
value in $^O is "riscos" (because we don't like shouting).
Other perls¶
Perl has been ported to many platforms that do not fit into any of the
categories listed above. Some, such as AmigaOS, QNX, Plan 9, and VOS, have
been well-integrated into the standard Perl source code kit. You may need to
see the
ports/ directory on CPAN for information, and possibly
binaries, for the likes of: aos, Atari ST, lynxos, riscos, Novell Netware,
Tandem Guardian,
etc. (Yes, we know that some of these OSes may fall
under the Unix category, but we are not a standards body.)
Some approximate operating system names and their $^O values in the
"OTHER" category include:
OS $^O $Config{'archname'}
------------------------------------------
Amiga DOS amigaos m68k-amigos
See also:
- •
- Amiga, README.amiga (installed as perlamiga).
- •
- 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
- "-w" only inspects the read-only file attribute
(FILE_ATTRIBUTE_READONLY), which determines whether the directory can be
deleted, not whether it can be written to. Directories always have read
and write access unless denied by discretionary access control lists
(DACLs). (Win32)
"-r", "-w", "-x", and "-o" tell
whether the file is accessible, which may not reflect UIC-based file
protections. (VMS)
"-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". (Win32, VMS, RISC OS)
"-g", "-k", "-l", "-u",
"-A" are not particularly meaningful. (Win32, VMS,
RISC OS)
"-p" is not particularly meaningful. (VMS, RISC OS)
"-d" is true if passed a device spec without an explicit
directory. (VMS)
"-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)
- alarm
- Emulated using timers that must be explicitly polled whenever Perl wants
to dispatch "safe signals" and therefore cannot interrupt
blocking system calls. (Win32)
- 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.opengroup.org/onlinepubs/009695399/functions/atan2.html>.
- binmode
- Meaningless. (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 good for changing "owner" read-write access,
"group", and "other" bits are meaningless. (Win32)
Only good for changing "owner" and "other" read-write
access. (RISC OS)
Access permissions are mapped onto VOS access-control list changes. (VOS)
The actual permissions set depend on the value of the "CYGWIN" in
the SYSTEM environment settings. (Cygwin)
Setting the exec bit on some locations (generally /sdcard) will return true
but not actually set the bit. (Android)
- chown
- Not implemented. (Win32, Plan 9, RISC OS)
Does nothing, but won't fail. (Win32)
A little funky, because VOS's notion of ownership is a little funky
(VOS).
- chroot
- Not implemented. (Win32, VMS, Plan 9, RISC OS, VOS)
- crypt
- May not be available if library or source was not provided when building
perl. (Win32)
Not implemented. (Android)
- dbmclose
- Not implemented. (VMS, Plan 9, VOS)
- dbmopen
- Not implemented. (VMS, Plan 9, VOS)
- dump
- Not useful. (RISC OS)
Not supported. (Cygwin, Win32)
Invokes VMS debugger. (VMS)
- exec
- "exec LIST" without the use of indirect object syntax
("exec PROGRAM LIST") may fall back to trying the shell if the
first spawn() fails. (Win32)
Does not automatically flush output handles on some platforms. (SunOS,
Solaris, HP-UX)
Not supported. (Symbian OS)
- 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. On
VMS, unless the future POSIX_EXIT mode is enabled, the exit code should
always be a valid VMS exit code and not a generic number. When the
POSIX_EXIT mode is enabled, a generic number will be encoded in a method
compatible with the C library _POSIX_EXIT macro so that it can be decoded
by other programs, particularly ones written in C, like the GNV package.
(VMS)
"exit()" resets file pointers, which is a problem when called from
a child process (created by "fork()") in "BEGIN". A
workaround is to use "POSIX::_exit". (Solaris)
exit unless $Config{archname} =~ /\bsolaris\b/;
require POSIX and POSIX::_exit(0);
- fcntl
- Not implemented. (Win32)
Some functions available based on the version of VMS. (VMS)
- flock
- Not implemented (VMS, RISC OS, VOS).
- fork
- Not implemented. (AmigaOS, RISC OS, VMS)
Emulated using multiple interpreters. See perlfork. (Win32)
Does not automatically flush output handles on some platforms. (SunOS,
Solaris, HP-UX)
- getlogin
- Not implemented. (RISC OS)
- getpgrp
- Not implemented. (Win32, VMS, RISC OS)
- getppid
- Not implemented. (Win32, RISC OS)
- getpriority
- Not implemented. (Win32, VMS, RISC OS, VOS)
- getpwnam
- Not implemented. (Win32)
Not useful. (RISC OS)
- getgrnam
- Not implemented. (Win32, VMS, RISC OS)
- getnetbyname
- Not implemented. (Android, Win32, Plan 9)
- getpwuid
- Not implemented. (Win32)
Not useful. (RISC OS)
- getgrgid
- Not implemented. (Win32, VMS, RISC OS)
- getnetbyaddr
- Not implemented. (Android, Win32, Plan 9)
- getprotobynumber
- Not implemented. (Android)
- getservbyport
- getpwent
- Not implemented. (Android, Win32)
- getgrent
- Not implemented. (Android, Win32, VMS)
- gethostbyname
- "gethostbyname('localhost')" does not work everywhere: you may
have to use "gethostbyname('127.0.0.1')". (Irix 5)
- gethostent
- Not implemented. (Win32)
- getnetent
- Not implemented. (Android, Win32, Plan 9)
- getprotoent
- Not implemented. (Android, Win32, Plan 9)
- getservent
- Not implemented. (Win32, Plan 9)
- seekdir
- Not implemented. (Android)
- sethostent
- Not implemented. (Android, Win32, Plan 9, RISC OS)
- setnetent
- Not implemented. (Win32, Plan 9, RISC OS)
- setprotoent
- Not implemented. (Android, Win32, Plan 9, RISC OS)
- setservent
- Not implemented. (Plan 9, Win32, RISC OS)
- endpwent
- Not implemented. (Win32)
Either not implemented or a no-op. (Android)
- endgrent
- Not implemented. (Android, RISC OS, VMS, Win32)
- endhostent
- Not implemented. (Android, Win32)
- endnetent
- Not implemented. (Android, Win32, Plan 9)
- endprotoent
- Not implemented. (Android, 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
- In theory, gmtime() is reliable from -2**63 to 2**63-1. However,
because work arounds in the implementation use floating point numbers, it
will become inaccurate as the time gets larger. This is a bug and will be
fixed in the future.
On VOS, time values are 32-bit quantities.
- 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
- 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)
"kill(-9, $pid)" will terminate the process specified by $pid and
recursively all child processes owned by it. This is different from the
Unix semantics, where the signal will be delivered to all processes in the
same process group as the process specified by $pid. (Win32)
Is not supported for process identification number of 0 or negative numbers.
(VMS)
- link
- Not implemented. (RISC OS, VOS)
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 under NTFS only. They are natively
supported on Windows 2000 and later. On Windows NT they are implemented
using the Windows POSIX subsystem support and the Perl process will need
Administrator or Backup Operator privileges to create hard links.
Available on 64 bit OpenVMS 8.2 and later. (VMS)
- localtime
- localtime() has the same range as "gmtime", but because
time zone rules change its accuracy for historical and future times may
degrade but usually by no more than an hour.
- lstat
- Not implemented. (RISC OS)
Return values (especially for device and inode) may be bogus. (Win32)
- msgctl
- msgget
- msgsnd
- msgrcv
- Not implemented. (Android, Win32, VMS, Plan 9, RISC OS,
VOS)
- open
- open to "|-" and "-|" are unsupported. (Win32,
RISC OS)
Opening a process does not automatically flush output handles on some
platforms. (SunOS, Solaris, HP-UX)
- readlink
- Not implemented. (Win32, VMS, RISC OS)
- rename
- Can't move directories between directories on different logical volumes.
(Win32)
- rewinddir
- Will not cause readdir() to re-read the directory stream. The
entries already read before the rewinddir() call will just be
returned again from a cache buffer. (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. (Android, Win32, VMS, RISC OS)
- setgrent
- Not implemented. (Android, VMS, Win32, RISC OS)
- setpgrp
- Not implemented. (Win32, VMS, RISC OS, VOS)
- setpriority
- Not implemented. (Win32, VMS, RISC OS, VOS)
- setpwent
- Not implemented. (Android, Win32, RISC OS)
- setsockopt
- Not implemented. (Plan 9)
- shmctl
- shmget
- shmread
- shmwrite
- Not implemented. (Android, Win32, VMS, RISC OS)
- sleep
- Emulated using synchronization functions such that it can be interrupted
by alarm(), and limited to a maximum of 4294967 seconds,
approximately 49 days. (Win32)
- sockatmark
- A relatively recent addition to socket functions, may not be implemented
even in Unix platforms.
- socketpair
- Not implemented. (RISC OS)
Available on 64 bit OpenVMS 8.2 and later. (VMS)
- 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.
ctime not supported on UFS (Mac OS X).
ctime is creation time instead of inode change time (Win32).
device and inode are not meaningful. (Win32)
device and inode are not necessarily reliable. (VMS)
mtime, atime and ctime all return the last modification time. Device and
inode are not necessarily reliable. (RISC OS)
dev, rdev, blksize, and blocks are not available. inode is not meaningful
and will differ between stat calls on the same file. (os2)
some versions of cygwin when doing a stat("foo") and if not
finding it may then attempt to stat("foo.exe") (Cygwin)
On Win32 stat() needs to open the file to determine the link count
and update attributes that may have been changed through hard links.
Setting ${^WIN32_SLOPPY_STAT} to a true value speeds up stat() by
not performing this operation. (Win32)
- symlink
- Not implemented. (Win32, RISC OS)
Implemented on 64 bit VMS 8.3. VMS requires the symbolic link to be in Unix
syntax if it is intended to resolve to a valid path.
- syscall
- Not implemented. (Win32, VMS, RISC OS, VOS)
- 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)
- system
- As an optimization, may not call the command shell specified in
$ENV{PERL5SHELL}. "system(1, @args)" spawns an external process
and immediately returns its process designator, without waiting for it to
terminate. Return value may be used subsequently in "wait" or
"waitpid". Failure to spawn() a subprocess is indicated
by setting $? to "255 << 8". $? is set in a way compatible
with Unix (i.e. the exitstatus of the subprocess is obtained by "$?
>> 8", as described in the documentation). (Win32)
There is no shell to process metacharacters, and the native standard is to
pass a command line terminated by "\n" "\r" or
"\0" to the spawned program. Redirection such as ">
foo" is performed (if at all) by the run time library of the spawned
program. "system" list will call the Unix emulation
library's "exec" emulation, which attempts to provide emulation
of the stdin, stdout, stderr in force in the parent, providing the child
program uses a compatible version of the emulation library. scalar
will call the native command line direct and no such emulation of a child
Unix program will exists. Mileage will vary. (RISC OS)
"system LIST" without the use of indirect object syntax
("system PROGRAM LIST") may fall back to trying the shell if the
first spawn() fails. (Win32)
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'"). If the native condition code is one that has a POSIX
value encoded, the POSIX value will be decoded to extract the expected
exit value. For more details see "$?" in perlvms. (VMS)
- telldir
- Not implemented. (Android)
- times
- "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 same-or-shorter lengths 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.
"umask" works but the correct permissions are set only when the
file is finally closed. (AmigaOS)
- utime
- Only the modification time is updated. (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
- 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)
The following platforms are known to build Perl 5.12 (as of April 2010, its
release date) from the standard source code distribution available at
<
http://www.cpan.org/src>
- Linux (x86, ARM, IA64)
- HP-UX
- AIX
- Win32
- Windows 2000
- Windows XP
- Windows Server 2003
- Windows Vista
- Windows Server 2008
- Windows 7
- Cygwin
- Some tests are known to fail:
- Solaris (x86, SPARC)
- OpenVMS
- Alpha (7.2 and later)
- I64 (8.2 and later)
- Symbian
- NetBSD
- FreeBSD
- Debian GNU/kFreeBSD
- Haiku
- Irix (6.5. What else?)
- OpenBSD
- Dragonfly BSD
- Midnight BSD
- QNX Neutrino RTOS (6.5.0)
- MirOS BSD
- Stratus OpenVOS (17.0 or later)
- Caveats:
- time_t issues that may or may not be fixed
- Symbian (Series 60 v3, 3.2 and 5 - what else?)
- Stratus VOS / OpenVOS
- AIX
- Android
- FreeMINT
- Perl now builds with FreeMiNT/Atari. It fails a few tests, that needs some
investigation.
The FreeMiNT port uses GNU dld for loadable module capabilities. So ensure
you have that library installed when building perl.
(Perl 5.20)¶
The following platforms were supported by a previous version of Perl but have
been officially removed from Perl's source code as of 5.20:
- AT&T 3b1
(Perl 5.14)¶
The following platforms were supported up to 5.10. They may still have worked in
5.12, but supporting code has been removed for 5.14:
- Windows 95
- Windows 98
- Windows ME
- Windows NT4
(Perl 5.12)¶
The following platforms were supported by a previous version of Perl but have
been officially removed from Perl's source code as of 5.12:
- Atari MiNT
- Apollo Domain/OS
- Apple Mac OS 8/9
- Tenon Machten
As of July 2002 (the Perl release 5.8.0), the following platforms were able to
build Perl from the standard source code distribution available at
<
http://www.cpan.org/src/>
AIX
BeOS
BSD/OS (BSDi)
Cygwin
DG/UX
DOS DJGPP 1)
DYNIX/ptx
EPOC R5
FreeBSD
HI-UXMPP (Hitachi) (5.8.0 worked but we didn't know it)
HP-UX
IRIX
Linux
Mac OS Classic
Mac OS X (Darwin)
MPE/iX
NetBSD
NetWare
NonStop-UX
ReliantUNIX (formerly SINIX)
OpenBSD
OpenVMS (formerly VMS)
Open UNIX (Unixware) (since Perl 5.8.1/5.9.0)
OS/2
OS/400 (using the PASE) (since Perl 5.8.1/5.9.0)
PowerUX
POSIX-BC (formerly BS2000)
QNX
Solaris
SunOS 4
SUPER-UX (NEC)
Tru64 UNIX (formerly DEC OSF/1, Digital UNIX)
UNICOS
UNICOS/mk
UTS
VOS / OpenVOS
Win95/98/ME/2K/XP 2)
WinCE
z/OS (formerly OS/390)
VM/ESA
1) in DOS mode either the DOS or OS/2 ports can be used
2) compilers: Borland, MinGW (GCC), VC6
The following platforms worked with the previous releases (5.6 and 5.7), but we
did not manage either to fix or to test these in time for the 5.8.0 release.
There is a very good chance that many of these will work fine with the 5.8.0.
BSD/OS
DomainOS
Hurd
LynxOS
MachTen
PowerMAX
SCO SV
SVR4
Unixware
Windows 3.1
Known to be broken for 5.8.0 (but 5.6.1 and 5.7.2 can be used):
AmigaOS
The following platforms have been known to build Perl from source in the past
(5.005_03 and earlier), but we haven't been able to verify their status for
the current release, either because the hardware/software platforms are rare
or because we don't have an active champion on these platforms--or both. They
used to work, though, so go ahead and try compiling them, and let
perlbug@perl.org of any trouble.
3b1
A/UX
ConvexOS
CX/UX
DC/OSx
DDE SMES
DOS EMX
Dynix
EP/IX
ESIX
FPS
GENIX
Greenhills
ISC
MachTen 68k
MPC
NEWS-OS
NextSTEP
OpenSTEP
Opus
Plan 9
RISC/os
SCO ODT/OSR
Stellar
SVR2
TI1500
TitanOS
Ultrix
Unisys Dynix
The following platforms have their own source code distributions and binaries
available via <
http://www.cpan.org/ports/>
Perl release
OS/400 (ILE) 5.005_02
Tandem Guardian 5.004
The following platforms have only binaries available via
<
http://www.cpan.org/ports/index.html> :
Perl release
Acorn RISCOS 5.005_02
AOS 5.002
LynxOS 5.004_02
Although we do suggest that you always build your own Perl from the source code,
both for maximal configurability and for security, in case you are in a hurry
you can check <
http://www.cpan.org/ports/index.html> for binary
distributions.
SEE ALSO¶
perlaix, perlamiga, perlbs2000, perlce, perlcygwin, perldos, perlebcdic,
perlfreebsd, perlhurd, perlhpux, perlirix, perlmacos, perlmacosx, perlnetware,
perlos2, perlos390, perlos400, perlplan9, perlqnx, perlsolaris, perltru64,
perlunicode, perlvms, perlvos, perlwin32, and Win32.
AUTHORS / CONTRIBUTORS¶
Abigail <abigail@foad.org>, Charles Bailey
<bailey@newman.upenn.edu>, Graham Barr <gbarr@pobox.com>, Tom
Christiansen <tchrist@perl.com>, Nicholas Clark <nick@ccl4.org>,
Thomas Dorner <Thomas.Dorner@start.de>, Andy Dougherty
<doughera@lafayette.edu>, Dominic Dunlop <domo@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>, John Malmberg <wb8tyw@qsl.net>