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perlport - Writing portable Perl
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perlport - Writing portable Perl
Perl runs on numerous operating systems. While most of them share
much in common, they also have their own unique features.
This document is meant to help you to find out what constitutes portable
Perl code. That way once you make a decision to write portably,
you know where the lines are drawn, and you can stay within them.
There is a tradeoff between taking full advantage of one particular
type of computer and taking advantage of a full range of them.
Naturally, as you broaden your range and become more diverse, the
common factors drop, and you are left with an increasingly smaller
area of common ground in which you can operate to accomplish a
particular task. Thus, when you begin attacking a problem, it is
important to consider under which part of the tradeoff curve you
want to operate. Specifically, you must decide whether it is
important that the task that you are coding have the full generality
of being portable, or whether to just get the job done right now.
This is the hardest choice to be made. The rest is easy, because
Perl provides many choices, whichever way you want to approach your
problem.
Looking at it another way, writing portable code is usually about
willfully limiting your available choices. Naturally, it takes
discipline and sacrifice to do that. The product of portability
and convenience may be a constant. You have been warned.
Be aware of two important points:
- 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,
Mac OS, VMS, etc.), consider writing platform-specific code.
When the code will run on only two or three operating systems, you
may need to consider only the differences of those particular systems.
The important thing is to decide where the code will run and to be
deliberate in your decision.
The material below is separated into three main sections: main issues of
portability (ISSUES, platform-specific issues (PLATFORMS, and
built-in perl functions that behave differently on various ports
(FUNCTION IMPLEMENTATIONS.
This information should not be considered complete; it includes possibly
transient information about idiosyncrasies of some of the ports, almost
all of which are in a state of constant evolution. Thus, this material
should be considered a perpetual work in progress
(<IMG SRC=``yellow_sign.gif'' ALT=``Under Construction''>).
In most operating systems, lines in files are terminated by newlines.
Just what is used as a newline may vary from OS to OS. Unix
traditionally uses \012, one type of DOSish I/O uses \015\012,
and Mac OS uses \015.
Perl uses \n to represent the ``logical'' newline, where what is
logical may depend on the platform in use. In MacPerl, \n always
means \015. In DOSish perls, \n usually means \012, but
when accessing a file in ``text'' mode, STDIO translates it to (or
from) \015\012, depending on whether you're reading or writing.
Unix does the same thing on ttys in canonical mode. \015\012
is commonly referred to as CRLF.
A common cause of unportable programs is the misuse of chop() to trim
newlines:
# XXX UNPORTABLE!
while(<FILE>) {
chop;
@array = split(/:/);
#...
}
You can get away with this on Unix and MacOS (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 $/ is \n, but robust socket code will recognize as
either \012 or \015\012 as end of line:
while (<SOCKET>) {
# ...
}
Because both CRLF and LF end in LF, the input record separator can
be set to LF and any CR stripped later. Better to write:
use Socket qw(:DEFAULT :crlf);
local($/) = 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 == \012 == \x0A == \cJ == ASCII 10
CR == \015 == \x0D == \cM == 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.
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.
You can explore the endianness of your platform by unpacking a
data structure packed in native format such as:
print unpack("h*", pack("s2", 1, 2)), "\n";
# '10002000' on e.g. Intel x86 or Alpha 21064 in little-endian mode
# '00100020' on e.g. Motorola 68040
If you need to distinguish between endian architectures you could use
either of the variables set like so:
$is_big_endian = unpack("h*", pack("s", 1)) =~ /01/;
$is_little_endian = unpack("h*", pack("s", 1)) =~ /^1/;
Differing widths can cause truncation even between platforms of equal
endianness. The platform of shorter width loses the upper parts of the
number. There is no good solution for this problem except to avoid
transferring or storing raw binary numbers.
One can circumnavigate both these problems in two ways. Either
transfer and store numbers always in text format, instead of raw
binary, or else consider using modules like Data::Dumper (included in
the standard distribution as of Perl 5.005) and Storable. Keeping
all data as text significantly simplifies matters.
Most platforms these days structure files in a hierarchical fashion.
So, it is reasonably safe to assume that all platforms support the
notion of a ``path'' to uniquely identify a file on the system. How
that path is really written, though, differs considerably.
Although similar, file path specifications differ between Unix,
Windows, Mac OS, OS/2, VMS, VOS, RISC OS, and probably others.
Unix, for example, is one of the few OSes that has the elegant idea
of a single root directory.
DOS, OS/2, VMS, VOS, and Windows can work similarly to Unix with /
as path separator, or in their own idiosyncratic ways (such as having
several root directories and various ``unrooted'' device files such NIL:
and LPT:).
Mac OS 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).
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.
If all this is intimidating, have no (well, maybe only a little)
fear. There are modules that can help. The File::Spec modules
provide methods to do the Right Thing on whatever platform happens
to be running the program.
use File::Spec::Functions;
chdir(updir()); # go up one directory
$file = catfile(curdir(), 'temp', 'file.txt');
# on Unix and Win32, './temp/file.txt'
# on Mac OS, ':temp:file.txt'
# on VMS, '[.temp]file.txt'
File::Spec is available in the standard distribution as of version
5.004_05. File::Spec::Functions is only in File::Spec 0.7 and later,
and some versions of perl come with version 0.6. If File::Spec
is not updated to 0.7 or later, you must use the object-oriented
interface from File::Spec (or upgrade File::Spec).
In general, production code should not have file paths hardcoded.
Making them user-supplied or read from a configuration file is
better, keeping in mind that file path syntax varies on different
machines.
This is especially noticeable in scripts like Makefiles and test suites,
which often assume / as a path separator for subdirectories.
Also of use is File::Basename from the standard distribution, which
splits a pathname into pieces (base filename, full path to directory,
and file suffix).
Even when on a single platform (if you can call Unix a single platform),
remember not to count on the existence or the contents of particular
system-specific files or directories, like /etc/passwd,
/etc/sendmail.conf, /etc/resolv.conf, or even /tmp/. For
example, /etc/passwd may exist but not contain the encrypted
passwords, because the system is using some form of enhanced security.
Or it may not contain all the accounts, because the system is using NIS.
If code does need to rely on such a file, include a description of the
file and its format in the code's documentation, then make it easy for
the user to override the default location of the file.
Don't assume a text file will end with a newline. They should,
but people forget.
Do not have two files of the same name with different case, like
test.pl and Test.pl, as many platforms have case-insensitive
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.
Many systems (DOS, VMS) cannot have more than one . in their filenames.
Don't assume > won't be the first character of a filename.
Always use < explicitly to open a file for reading,
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.)
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.
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 count on a specific environment variable existing in %ENV.
Don't count on %ENV entries being case-sensitive, or even
case-preserving. Don't try to clear %ENV by saying %ENV = ();, or,
if you really have to, make it conditional on $^O ne 'VMS' since in
VMS the %ENV table is much more than a per-process key-value string
table.
Don't count on signals or %SIG for anything.
Don't count on filename globbing. Use opendir, readdir, and
closedir instead.
Don't count on per-program environment variables, or per-program current
directories.
Don't count on specific values of $!.
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.
The rule of thumb for portable code is: Do it all in portable Perl, or
use a module (that may internally implement it with platform-specific
code, but expose a common interface).
XS code can usually be made to work with any platform, but dependent
libraries, header files, etc., might not be readily available or
portable, or the XS code itself might be platform-specific, just as Perl
code might be. If the libraries and headers are portable, then it is
normally reasonable to make sure the XS code is portable, too.
A different type of portability issue arises when writing XS code:
availability of a C compiler on the end-user's system. C brings
with it its own portability issues, and writing XS code will expose
you to some of those. Writing purely in Perl is an easier way to
achieve portability.
In general, the standard modules work across platforms. Notable
exceptions are the CPAN module (which currently makes connections to external
programs that may not be available), platform-specific modules (like
ExtUtils::MM_VMS), and DBM modules.
There is no one DBM module available on all platforms.
SDBM_File and the others are generally available on all Unix and DOSish
ports, but not in MacPerl, where only NBDM_File and DB_File are
available.
The good news is that at least some DBM module should be available, and
AnyDBM_File will use whichever module it can find. Of course, then
the code needs to be fairly strict, dropping to the greatest common
factor (e.g., not exceeding 1K for each record), so that it will
work with any DBM module. See the AnyDBM_File manpage for more details.
The system's notion of time of day and calendar date is controlled in
widely different ways. Don't assume the timezone is stored in $ENV{TZ},
and even if it is, don't assume that you can control the timezone through
that variable.
Don't assume 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. A text representation (like ``1987-12-18'')
can be easily converted into an OS-specific value using a module like
Date::Parse. An array of values, such as those returned by
localtime, can be converted to an OS-specific representation using
Time::Local.
When calculating specific times, such as for tests in time or date modules,
it may be appropriate to calculate an offset for the epoch.
require Time::Local;
$offset = Time::Local::timegm(0, 0, 0, 1, 0, 70);
The value for $offset in Unix will be 0, but in Mac OS will be
some large number. $offset can then be added to a Unix time value
to get what should be the proper value on any system.
Assume little about character sets. Assume nothing about
numerical values (ord, chr) of characters. Do not
assume that the alphabetic characters are encoded contiguously (in
the numeric sense). Do not assume anything about the ordering of the
characters. The lowercase letters may come before or after the
uppercase letters; the lowercase and uppercase may be interlaced so
that both `a' and `A' come before `b'; the accented and other
international characters may be interlaced so that ä comes
before `b'.
If you may assume POSIX (a rather large assumption), you may read
more about the POSIX locale system from the perllocale manpage. The locale
system at least attempts to make things a little bit more portable,
or at least more convenient and native-friendly for non-English
users. The system affects character sets and encoding, and date
and time formatting--amongst other things.
If your code is destined for systems with severely constrained (or
missing!) virtual memory systems then you want to be especially mindful
of avoiding wasteful constructs such as:
# NOTE: this is no longer "bad" in perl5.005
for (0..10000000) {} # bad
for (my $x = 0; $x <= 10000000; ++$x) {} # good
@lines = <VERY_LARGE_FILE>; # bad
while (<FILE>) {$file .= $_} # sometimes bad
$file = join('', <FILE>); # better
The last two constructs may appear unintuitive to most people. The
first repeatedly grows a string, whereas the second allocates a
large chunk of memory in one go. On some systems, the second is
more efficient that the first.
Most multi-user platforms provide basic levels of security, usually
implemented at the filesystem level. Some, however, do
not--unfortunately. Thus the notion of user id, or ``home'' directory,
or even the state of being logged-in, may be unrecognizable on many
platforms. If you write programs that are security-conscious, it
is usually best to know what type of system you will be running
under so that you can write code explicitly for that platform (or
class of platforms).
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 an system call. Some platforms expect a certain
output format, and perl on those platforms may have been adjusted
accordingly. Most specifically, don't anchor a regex when testing
an error value.
Modules uploaded to CPAN are tested by a variety of volunteers on
different platforms. These CPAN testers are notified by mail of each
new upload, and reply to the list with PASS, FAIL, NA (not applicable to
this platform), or UNKNOWN (unknown), along with any relevant notations.
The purpose of the testing is twofold: one, to help developers fix any
problems in their code that crop up because of lack of testing on other
platforms; two, to provide users with information about whether
a given module works on a given platform.
- Mailing list: cpan-testers@perl.org
-
- Testing results: http://testers.cpan.org/
-
As of version 5.002, Perl is built with a $^O variable that
indicates the operating system it was built on. This was implemented
to help speed up code that would otherwise have to use Config
and use the value of $Config{osname}. Of course, to get more
detailed information about the system, looking into %Config is
certainly recommended.
%Config cannot always be trusted, however, because it was built
at compile time. If perl was built in one place, then transferred
elsewhere, some values may be wrong. The values may even have been
edited after the fact.
Perl works on a bewildering variety of Unix and Unix-like platforms (see
e.g. most of the files in the hints/ directory in the source code kit).
On most of these systems, the value of $^O (hence $Config{'osname'},
too) is determined either by lowercasing and stripping punctuation from the
first field of the string returned by typing uname -a (or a similar command)
at the shell prompt or by testing the file system for the presence of
uniquely named files such as a kernel or header file. Here, for example,
are a few of the more popular Unix flavors:
uname $^O $Config{'archname'}
--------------------------------------------
AIX aix aix
BSD/OS bsdos i386-bsdos
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 rhapsody rhapsody
MachTen PPC machten powerpc-machten
NeXT 3 next next-fat
NeXT 4 next OPENSTEP-Mach
openbsd openbsd i386-openbsd
OSF1 dec_osf alpha-dec_osf
reliantunix-n svr4 RM400-svr4
SCO_SV sco_sv i386-sco_sv
SINIX-N svr4 RM400-svr4
sn4609 unicos CRAY_C90-unicos
sn6521 unicosmk t3e-unicosmk
sn9617 unicos CRAY_J90-unicos
SunOS solaris sun4-solaris
SunOS solaris i86pc-solaris
SunOS4 sunos sun4-sunos
Because the value of $Config{archname} may depend on the
hardware architecture, it can vary more than the value of $^O.
Perl has long been ported to Intel-style microcomputers running under
systems like PC-DOS, MS-DOS, OS/2, and most Windows platforms you can
bring yourself to mention (except for Windows CE, if you count that).
Users familiar with COMMAND.COM or CMD.EXE style shells should
be aware that each of these file specifications may have subtle
differences:
$filespec0 = "c:/foo/bar/file.txt";
$filespec1 = "c:\\foo\\bar\\file.txt";
$filespec2 = 'c:\foo\bar\file.txt';
$filespec3 = 'c:\\foo\\bar\\file.txt';
System calls accept either / or \ as the path separator.
However, many command-line utilities of DOS vintage treat / as
the option prefix, so may get confused by filenames containing /.
Aside from calling any external programs, / will work just fine,
and probably better, as it is more consistent with popular usage,
and avoids the problem of remembering what to backwhack and what
not to.
The DOS FAT filesystem can accommodate only ``8.3'' style filenames. Under
the ``case-insensitive, but case-preserving'' HPFS (OS/2) and NTFS (NT)
filesystems you may have to be careful about case returned with functions
like readdir or used with functions like open or opendir.
DOS also treats several filenames as special, such as AUX, PRN,
NUL, CON, COM1, LPT1, LPT2, etc. Unfortunately, sometimes these
filenames won't even work if you include an explicit directory
prefix. It is best to avoid such filenames, if you want your code
to be portable to DOS and its derivatives. It's hard to know what
these all are, unfortunately.
Users of these operating systems may also wish to make use of
scripts such as pl2bat.bat or pl2cmd to
put wrappers around your scripts.
Newline (\n) is translated as \015\012 by STDIO when reading from
and writing to files (see Newlines). binmode(FILEHANDLE)
will keep \n translated as \012 for that filehandle. Since it is a
no-op on other systems, binmode should be used for cross-platform code
that deals with binary data. That's assuming you realize in advance
that your data is in binary. General-purpose programs should
often assume nothing about their data.
The $^O variable and the $Config{archname} values for various
DOSish perls are as follows:
OS $^O $Config{'archname'}
--------------------------------------------
MS-DOS dos
PC-DOS dos
OS/2 os2
Windows 95 MSWin32 MSWin32-x86
Windows 98 MSWin32 MSWin32-x86
Windows NT MSWin32 MSWin32-x86
Windows NT MSWin32 MSWin32-ALPHA
Windows NT MSWin32 MSWin32-ppc
Cygwin cygwin
The various MSWin32 Perl's can distinguish the OS they are running on
via the value of the fifth element of the list returned from
Win32::GetOSVersion(). For example:
if ($^O eq 'MSWin32') {
my @os_version_info = Win32::GetOSVersion();
print +('3.1','95','NT')[$os_version_info[4]],"\n";
}
Also see:
Any module requiring XS compilation is right out for most people, because
MacPerl is built using non-free (and non-cheap!) compilers. Some XS
modules that can work with MacPerl are built and distributed in binary
form on CPAN.
Directories are specified as:
volume:folder:file for absolute pathnames
volume:folder: for absolute pathnames
:folder:file for relative pathnames
:folder: for relative pathnames
:file for relative pathnames
file for relative pathnames
Files are stored in the directory in alphabetical order. Filenames are
limited to 31 characters, and may include any character except for
null and :, which is reserved as the path separator.
Instead of flock, see FSpSetFLock and FSpRstFLock in the
Mac::Files module, or chmod(0444, ...) and chmod(0666, ...).
In the MacPerl application, you can't run a program from the command line;
programs that expect @ARGV to be populated can be edited with something
like the following, which brings up a dialog box asking for the command
line arguments.
if (!@ARGV) {
@ARGV = split /\s+/, MacPerl::Ask('Arguments?');
}
A MacPerl script saved as a ``droplet'' will populate @ARGV with the full
pathnames of the files dropped onto the script.
Mac users can run programs under a type of command line interface
under MPW (Macintosh Programmer's Workshop, a free development
environment from Apple). MacPerl was first introduced as an MPW
tool, and MPW can be used like a shell:
perl myscript.plx some arguments
ToolServer is another app from Apple that provides access to MPW tools
from MPW and the MacPerl app, which allows MacPerl programs to use
system, backticks, and piped open.
``Mac OS'' is the proper name for the operating system, but the value
in $^O is ``MacOS''. To determine architecture, version, or whether
the application or MPW tool version is running, check:
$is_app = $MacPerl::Version =~ /App/;
$is_tool = $MacPerl::Version =~ /MPW/;
($version) = $MacPerl::Version =~ /^(\S+)/;
$is_ppc = $MacPerl::Architecture eq 'MacPPC';
$is_68k = $MacPerl::Architecture eq 'Mac68K';
Mac OS X and Mac OS X Server, based on NeXT's OpenStep OS, will
(in theory) be able to run MacPerl natively, under the ``Classic''
environment. The new ``Cocoa'' environment (formerly called the ``Yellow Box'')
may run a slightly modified version of MacPerl, using the Carbon interfaces.
Mac OS X Server and its Open Source version, Darwin, both run Unix
perl natively (with a few patches). Full support for these
is slated for perl 5.6.
Also see:
Perl on VMS is discussed in the perlvms manpage in the perl distribution.
Perl on VMS can accept either VMS- or Unix-style file
specifications as in either of the following:
$ perl -ne "print if /perl_setup/i" SYS$LOGIN:LOGIN.COM
$ perl -ne "print if /perl_setup/i" /sys$login/login.com
but not a mixture of both as in:
$ perl -ne "print if /perl_setup/i" sys$login:/login.com
Can't open sys$login:/login.com: file specification syntax error
Interacting with Perl from the Digital Command Language (DCL) shell
often requires a different set of quotation marks than Unix shells do.
For example:
$ perl -e "print ""Hello, world.\n"""
Hello, world.
There are several ways to wrap your perl scripts in DCL .COM files, if
you are so inclined. For example:
$ write sys$output "Hello from DCL!"
$ if p1 .eqs. ""
$ then perl -x 'f$environment("PROCEDURE")
$ else perl -x - 'p1 'p2 'p3 'p4 'p5 'p6 'p7 'p8
$ deck/dollars="__END__"
#!/usr/bin/perl
print "Hello from Perl!\n";
__END__
$ endif
Do take care with $ ASSIGN/nolog/user SYS$COMMAND: SYS$INPUT if your
perl-in-DCL script expects to do things like $read = <STDIN>;.
Filenames are in the format ``name.extension;version''. The maximum
length for filenames is 39 characters, and the maximum length for
extensions is also 39 characters. Version is a number from 1 to
32767. Valid characters are /[A-Z0-9$_-]/.
VMS's RMS filesystem is case-insensitive and does not preserve case.
readdir returns lowercased filenames, but specifying a file for
opening remains case-insensitive. Files without extensions have a
trailing period on them, so doing a readdir with a file named A.;5
will return a. (though that file could be opened with
open(FH, 'A')).
RMS had an eight level limit on directory depths from any rooted logical
(allowing 16 levels overall) prior to VMS 7.2. Hence
PERL_ROOT:[LIB.2.3.4.5.6.7.8] is a valid directory specification but
PERL_ROOT:[LIB.2.3.4.5.6.7.8.9] is not. Makefile.PL authors might
have to take this into account, but at least they can refer to the former
as /PERL_ROOT/lib/2/3/4/5/6/7/8/.
The VMS::Filespec module, which gets installed as part of the build
process on VMS, is a pure Perl module that can easily be installed on
non-VMS platforms and can be helpful for conversions to and from RMS
native formats.
What \n represents depends on the type of file opened. It could
be \015, \012, \015\012, or nothing. The VMS::Stdio module
provides access to the special fopen() requirements of files with unusual
attributes on VMS.
TCP/IP stacks are optional on VMS, so socket routines might not be
implemented. UDP sockets may not be supported.
The value of $^O on OpenVMS is ``VMS''. To determine the architecture
that you are running on without resorting to loading all of %Config
you can examine the content of the @INC array like so:
if (grep(/VMS_AXP/, @INC)) {
print "I'm on Alpha!\n";
} elsif (grep(/VMS_VAX/, @INC)) {
print "I'm on VAX!\n";
} else {
print "I'm not so sure about where $^O is...\n";
}
On VMS, perl determines the UTC offset from the SYS$TIMEZONE_DIFFERENTIAL
logical name. Although the VMS epoch began at 17-NOV-1858 00:00:00.00,
calls to localtime are adjusted to count offsets from
01-JAN-1970 00:00:00.00, just like Unix.
Also see:
Perl on VOS is discussed in README.vos in the perl distribution
(installed as the perlvos manpage). Perl on VOS can accept either VOS- or
Unix-style file specifications as in either of the following:
$ 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. Note that VOS limits
file names to 32 or fewer characters.
See README.vos for restrictions that apply when Perl is built
with the alpha version of VOS POSIX.1 support.
Perl on VOS is built without any extensions and does not support
dynamic loading.
The value of $^O on VOS is ``VOS''. To determine the architecture that
you are running on without resorting to loading all of %Config you
can examine the content of the @INC array like so:
if ($^O =~ /VOS/) {
print "I'm on a Stratus box!\n";
} else {
print "I'm not on a Stratus box!\n";
die;
}
if (grep(/860/, @INC)) {
print "This box is a Stratus XA/R!\n";
} elsif (grep(/7100/, @INC)) {
print "This box is a Stratus HP 7100 or 8xxx!\n";
} elsif (grep(/8000/, @INC)) {
print "This box is a Stratus HP 8xxx!\n";
} else {
print "This box is a Stratus 68K!\n";
}
Also see:
-
README.vos
-
The VOS mailing list.
There is | 
