++ed by:

136 PAUSE users
117 non-PAUSE users.

Gurusamy Sarathy

# NAME

perlport - Writing portable Perl

# DESCRIPTION

Perl runs on a variety of operating systems. While most of them share a lot in common, they also have their own very particular and unique features.

This document is meant to help you to find out what constitutes portable perl code, so that once you have made your 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 a particular type of computer, and taking advantage of a full range of them. Naturally, as you make your range bigger (and thus more diverse), the common denominators drop, and you are left with fewer areas 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 which part of the tradeoff curve you want to operate under. Specifically, whether it is important to you that the task that you are coding needs the full generality of being portable, or if it is sufficient to just get the job done. This is the hardest choice to be made. The rest is easy, because Perl provides lots of 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 to do that.

Be aware of two important points:

Not all Perl programs have to be portable

There is no reason why 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.

The vast majority of Perl 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 that is commonly done using a whole range of platforms, think in terms of 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, then you may only need to consider the differences of those particular systems. The important thing is to decide where the code will run, and to be deliberate in your decision.

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 separated with newlines. Just what is used as a newline may vary from OS to OS. Unix traditionally uses \012, one kind of Windows 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.

Due to the "text" mode translation, DOSish perls have limitations of using seek and tell when a file is being accessed in "text" mode. Specifically, if you stick to seek-ing to locations you got from tell (and no others), you are usually free to use seek and tell even in "text" mode. In general, using seek or tell or other file operations that count bytes instead of characters, without considering the length of \n, may be non-portable. If you use binmode on a file, however, you can usually use seek and tell with arbitrary values quite safely.

A common misconception in socket programming is that \n eq \012 everywhere. When using protocols, such as common Internet protocols, \012 and \015 are called for specifically, and the values of the logical \n and \r (carriage return) are not reliable.

    print SOCKET "Hi there, client!\r\n";      # WRONG
print SOCKET "Hi there, client!\015\012";  # RIGHT

[NOTE: this does not necessarily apply to communications that are filtered by another program or module before sending to the socket; the the most popular EBCDIC webserver, for instance, accepts \r\n, which translates those characters, along with all other characters in text streams, from EBCDIC to ASCII.]

However, \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 code like this should recognize $/ as \012 or \015\012:  while (<SOCKET>) { # ... } Better:  use Socket qw(:DEFAULT :crlf); local($/) = LF;      # not needed if $/ is already \012 while (<SOCKET>) { s/$CR?$LF/\n/; # not sure if socket uses LF or CRLF, OK # s/\015?\012/\n/; # same thing } And this example is actually better than the previous one even for Unix platforms, because now any \015's (\cM's) are stripped out (and there was much rejoicing). ## File Paths Most platforms these days structure files in a hierarchical fashion. So, it is reasonably safe to assume that any platform supports the notion of a "path" to uniquely identify a file on the system. Just how that path is actually written, differs. While they are similar, file path specifications differ between Unix, Windows, Mac OS, OS/2, VMS, RISC OS and probably others. Unix, for example, is one of the few OSes that has the idea of a root directory. Mac OS uses : as a path separator instead of /. VMS, Windows, and OS/2 can work similarly to Unix with / as path separator, or in their own idiosyncratic ways. RISC OS perl can emulate Unix filenames with / as path separator, or go native and use . for path separator and : to signal filing systems and disc names. As with the newline problem above, there are modules that can help. The File::Spec modules provide methods to do the Right Thing on whatever platform happens to be running the program.  use File::Spec; chdir(File::Spec->updir()); # go up one directory$file = File::Spec->catfile(
File::Spec->curdir(), 'temp', 'file.txt'
);
# on Unix and Win32, './temp/file.txt'
# on Mac OS, ':temp:file.txt'

File::Spec is available in the standard distribution, as of version 5.004_05.

In general, production code should not have file paths hardcoded; making them user supplied or 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).

Remember not to count on the existence of system-specific files, like /etc/resolv.conf. If code does need to rely on such a file, include a description of the file and its format in the code's documentation, and make it easy for the user to override the default location of the file.

Don't assume that a you can open a full pathname for input with open (FILE, $name), as some platforms can use characters such as < which will perl open will interpret and eat. ## System Interaction Not all platforms provide for the notion of a command line, necessarily. These are usually platforms that rely on a Graphical User Interface (GUI) for user interaction. So a program requiring command lines might not work everywhere. But this is probably for the user of the program to deal with. Some platforms can't delete or rename files that are being held open by the system. Remember to close files when you are done with them. Don't unlink or rename an open file. Don't tie to or open a file that is already tied to or opened; untie or close first. Don't count on a specific environment variable existing in %ENV. Don't even count on %ENV entries being case-sensitive, or even case-preserving. Don't count on signals in portable programs. Don't count on filename globbing. Use opendir, readdir, and closedir instead. Don't count on per-program environment variables, or per-program current directores. ## Interprocess Communication (IPC) In general, don't directly access the system in code that is meant to be portable. That means, no: system, exec, fork, pipe, , qx//, open with a |, or any of the other things that makes being a Unix perl hacker worth being. Commands that launch external processes are generally supported on most platforms (though many of them do not support any type of forking), but the problem with using them arises from what you invoke with them. External tools are often named differently on different platforms, often not available in the same location, often accept different arguments, often behave differently, and often represent their results in a platform-dependent way. Thus you should seldom depend on them to produce consistent results. One especially common bit of Perl code is opening a pipe to sendmail:  open(MAIL, '|/usr/lib/sendmail -t') or die$!;

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 Mail::Send and Mail::Mailer modules in the MailTools distribution. Mail::Mailer provides several mailing methods, including mail, sendmail, and direct SMTP (via Net::SMTP) if a mail transfer agent is not available.

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. By portable Perl, we mean code that avoids the constructs described in this document as being non-portable.

## External Subroutines (XS)

XS code, in general, can 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.

There is a different kind of portability issue with 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 a comparatively easier way to achieve portability.

## Standard Modules

In general, the standard modules work across platforms. Notable exceptions are CPAN.pm (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 that is available on all platforms. SDBM_File and the others are generally available on all Unix and DOSish ports, but not in MacPerl, where 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 lowest common denominator (e.g., not exceeding 1K for each record).

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 $ENV{TZ}, and even if it is, don't assume that you can control the timezone through that variable. Don't assume that the epoch starts at January 1, 1970, because that is OS-specific. Better to store a date in an unambiguous representation. A text representation (like 1 Jan 1970) can be easily converted into an OS-specific value using a module like Date::Parse. An array of values, such as those returned by localtime, can be converted to an OS-specific representation using Time::Local. ## System Resources If your code is destined for systems with severely constrained (or missing!) virtual memory systems then you want to be especially mindful of avoiding wasteful constructs such as:  # NOTE: this is no longer "bad" in perl5.005 for (0..10000000) {} # bad for (my$x = 0; $x <= 10000000; ++$x) {}   # good

while (<FILE>) {$file .=$_}               # sometimes bad

# CPAN TESTERS

Module uploaded to CPAN are tested by a variety of volunteers on different platforms. These CPAN testers are notified by e-mail of each new upload, and reply to the list with PASS, FAIL, NA (not applicable to this platform), or ???? (unknown), along with any relevant notations.

The purpose of the testing is twofold: one, to help developers fix any problems in their code; two, to provide users with information about whether or not a given module works on a given platform.

Mailing list: cpan-testers@perl.org
Testing results: http://www.connect.net/gbarr/cpan-test/

# PLATFORMS

As of version 5.002, Perl is built with a $^O variable that indicates the operating system it was built on. This was implemented to help speed up code that would otherwise have to use Config; and use the value of $Config{'osname'}. Of course, to get detailed information about the system, looking into %Config is certainly recommended.

## 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 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. Here, for example, are a few of the more popular Unix flavors:

    uname        $^O$Config{'archname'}
-------------------------------------------
AIX          aix
FreeBSD      freebsd
Linux        linux
HP-UX        hpux
OSF1         dec_osf
SunOS        solaris    sun4-solaris
SunOS        solaris    i86pc-solaris
SunOS4       sunos

## DOS and Derivatives

Perl has long been ported to PC 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 and/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 they 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 file system can only accommodate "8.3" style filenames. Under the "case insensitive, but case preserving" HPFS (OS/2) and NTFS (NT) file systems 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 these filenames won't even work if you include an explicit directory prefix, in some cases. It is best to avoid such filenames, if you want your code to be portable to DOS and its derivatives.

Users of these operating systems may also wish to make use of scripts such as pl2bat.bat or pl2cmd as appropriate to put wrappers around your scripts.

Newline (\n) is translated as \015\012 by STDIO when reading from and writing to files. binmode(FILEHANDLE) will keep \n translated as \012 for that filehandle. Since it is a noop on other systems, binmode should be used for cross-platform code that deals with binary 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 NT    MSWin32    MSWin32-x86
Windows NT    MSWin32    MSWin32-alpha
Windows NT    MSWin32    MSWin32-ppc

Also see:

The djgpp environment for DOS, http://www.delorie.com/djgpp/
The EMX environment for DOS, OS/2, etc. emx@iaehv.nl, http://www.juge.com/bbs/Hobb.19.html
Build instructions for Win32, perlwin32.
The ActiveState Pages, http://www.activestate.com/

## MacPerl

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. See MacPerl: Power and Ease for more details.

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 in a directory are stored in alphabetical order. Filenames are limited to 31 characters, and may include any character except :, which is reserved as a path separator.

Instead of flock, see FSpSetFLock and FSpRstFLock in Mac::Files.

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) {
}

A MacPerl script saved as a droplet will populate @ARGV with the full pathnames of the files dropped onto the script.

Mac users can use programs on a kind of command line 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 program 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'; Also see: The MacPerl Pages, http://www.ptf.com/macperl/. The MacPerl mailing list, mac-perl-request@iis.ee.ethz.ch. ## VMS Perl on VMS is discussed in vms/perlvms.pod in the perl distribution. Note that 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 a number of 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' 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 that is open. It could be \015, \012, \015\012, or nothing. Reading from a file translates newlines to \012, unless binmode was executed on that handle, just like DOSish perls.

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";
}

Also see:

perlvms.pod
vmsperl list, vmsperl-request@newman.upenn.edu

Put words SUBSCRIBE VMSPERL in message body.

vmsperl on the web, http://www.sidhe.org/vmsperl/index.html

## EBCDIC Platforms

Recent versions of Perl have been ported to platforms such as OS/400 on AS/400 minicomputers as well as OS/390 for IBM Mainframes. Such computers use EBCDIC character sets internally (usually Character Code Set ID 00819 for OS/400 and IBM-1047 for OS/390). Note that on the mainframe perl currently works under the "Unix system services for OS/390" (formerly known as OpenEdition).

As of R2.5 of USS for OS/390 that Unix sub-system did not support the #! shebang trick for script invocation. Hence, on OS/390 perl scripts can 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"; On these platforms, bear in mind that the EBCDIC character set may have an effect on what happens with 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 (note that \r is the same under both ASCII and EBCDIC):  print "Content-type: text/html\r\n\r\n"; The value of $^O on OS/390 is "os390".

Some simple tricks for determining if you are running on an EBCDIC platform could include any of the following (perhaps all):

    if ("\t" eq "\05")   { print "EBCDIC may be spoken here!\n"; }

if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; }

if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; }

Note that 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:

perl-mvs list

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

## Acorn RISC OS

As Acorns use ASCII with newlines (\n) in text files as \012 like Unix and Unix filename emulation is turned on by default, it is quite likely that most simple scripts will work "out of the box". The native filing system is modular, and individual filing systems are free to be case sensitive or insensitive, usually case preserving. Some native filing systems have name length limits which file and directory names are silently truncated to fit - scripts should be aware that the standard disc filing system currently has a name length limit of 10 characters, with up to 77 items in a directory, but other filing systems may not impose such limitations.

Native filenames are of the form

    Filesystem#Special_Field::DiscName.$.Directory.Directory.File  where  Special_Field is not usually present, but may contain . and$ .
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::HardDisc.$.File" ne 'ADFS::HardDisc.$.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$Path until a name is made that points to an object on disc. Writing to a new file System:Modules would only be allowed if System$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 allows a user defined list of known suffixes which it will transpose in this fashion. This may appear 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 '/'. RISC OS has "image files", files that behave as directories. For example with suitable software this allows the contents of a zip file to be treated as a directory at command line (and therefore script) level, with full read-write random access. At present the perl port treats images as directories: -d returns true, -f false, and unlink checks to ensure that recognised images are empty before deleting them. In theory images should never trouble a script, but in practice they may do so if the software to deal with an image file is loaded and registered while the script is running, as suddenly "files" that it had cached information on metamorphose into directories. 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 filing system maintains a current directory, and the current filing system's current directory is the global current directory. Consequently sociable scripts don't change the current directory but rely on full pathnames, and scripts (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).

As native operating system filehandles are global and currently are 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. Run time libraries perform command line processing to emulate Unix shell style > redirection, but the core operating system is written in assembler and has its own private, obscure and somewhat broken convention. All this is further complicated by the desire of users to express filenames of the form <Foo$Dir>.Bar on the command line unquoted. (Oh yes, it's run time libraries interpreting the quoting convention.) Hence  command output capture has to perform a guessing game as to how the command is going to interpret the command line so that it can bodge it correctly to capture output. 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. Despite all this 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 the Acorn platform is used to binary distribution. MakeMaker does itself run, but no make currently copes with MakeMaker's makefiles! Even if (when) this is fixed os that the lack of a Unix-like shell can cause problems with makefile rules, especially lines of the form cd sdbm && make all and anything using quoting.

## Alphabetical Listing of Perl Functions

-X FILEHANDLE
-X EXPR
-X

-r, -w, and -x have only a very limited meaning; directories and applications are executable, and there are no uid/gid considerations. -o is not supported. (Mac OS)

-r, -w, -x, and -o tell whether or not file is accessible, which may not reflect UIC-based file protections. (VMS)

-s returns the size of the data fork, not the total size of data fork plus resource fork. (Mac OS).

-s by name on an open file will return the space reserved on disk, rather than the current extent. -s on an open filehandle returns the current size. (RISC OS)

-R, -W, -X, -O are indistinguishable from -r, -w, -x, -o. (Mac OS, Win32, VMS, RISC OS)

-b, -c, -k, -g, -p, -u, -A are not implemented. (Mac OS)

-g, -k, -l, -p, -u, -A are not particularly meaningful. (Win32, VMS, RISC OS)

-d is true if passed a device spec without an explicit directory. (VMS)

-T and -B are implemented, but might misclassify Mac text files with foreign characters; this is the case will all platforms, but affects Mac OS a lot. (Mac OS)

-x (or -X) determine if a file ends in one of the executable suffixes. -S is meaningless. (Win32)

-x (or -X) determine if a file has an executable file type. (RISC OS)

binmode FILEHANDLE

Meaningless. (Mac OS, RISC OS)

Reopens file and restores pointer; if function fails, underlying filehandle may be closed, or pointer may be in a different position. (VMS)

The value returned by tell may be affected after the call, and the filehandle may be flushed. (Win32)

chmod LIST

Only limited meaning. Disabling/enabling write permission is mapped to locking/unlocking the file. (Mac OS)

Only good for changing "owner" read-write access, "group", and "other" bits are meaningless. (Win32)

Only good for changing "owner" and "other" read-write access. (RISC OS)

chown LIST

Not implemented. (Mac OS, Win32, Plan9, RISC OS)

Does nothing, but won't fail. (Win32)

chroot FILENAME
chroot

Not implemented. (Mac OS, Win32, VMS, Plan9, RISC OS)

crypt PLAINTEXT,SALT

May not be available if library or source was not provided when building perl. (Win32)

dbmclose HASH

Not implemented. (VMS, Plan9)

dbmopen HASH,DBNAME,MODE

Not implemented. (VMS, Plan9)

dump LABEL

Not useful. (Mac OS, RISC OS)

Not implemented. (Win32)

Invokes VMS debugger. (VMS)

exec LIST

Not implemented. (Mac OS)

fcntl FILEHANDLE,FUNCTION,SCALAR

Not implemented. (Win32, VMS)

flock FILEHANDLE,OPERATION

Not implemented (Mac OS, VMS, RISC OS).

Available only on Windows NT (not on Windows 95). (Win32)

fork

Not implemented. (Mac OS, Win32, AmigaOS, RISC OS)

Not implemented. (Mac OS, RISC OS)

getpgrp PID

Not implemented. (Mac OS, Win32, VMS, RISC OS)

getppid

Not implemented. (Mac OS, Win32, VMS, RISC OS)

getpriority WHICH,WHO

Not implemented. (Mac OS, Win32, VMS, RISC OS)

getpwnam NAME

Not implemented. (Mac OS, Win32)

Not useful. (RISC OS)

getgrnam NAME

Not implemented. (Mac OS, Win32, VMS, RISC OS)

getnetbyname NAME

Not implemented. (Mac OS, Win32, Plan9)

getpwuid UID

Not implemented. (Mac OS, Win32)

Not useful. (RISC OS)

getgrgid GID

Not implemented. (Mac OS, Win32, VMS, RISC OS)

Not implemented. (Mac OS, Win32, Plan9)

getprotobynumber NUMBER

Not implemented. (Mac OS)

getservbyport PORT,PROTO

Not implemented. (Mac OS)

getpwent

Not implemented. (Mac OS, Win32)

getgrent

Not implemented. (Mac OS, Win32, VMS)

gethostent

Not implemented. (Mac OS, Win32)

getnetent

Not implemented. (Mac OS, Win32, Plan9)

getprotoent

Not implemented. (Mac OS, Win32, Plan9)

getservent

Not implemented. (Win32, Plan9)

setpwent

Not implemented. (Mac OS, Win32, RISC OS)

setgrent

Not implemented. (Mac OS, Win32, VMS, RISC OS)

sethostent STAYOPEN

Not implemented. (Mac OS, Win32, Plan9, RISC OS)

setnetent STAYOPEN

Not implemented. (Mac OS, Win32, Plan9, RISC OS)

setprotoent STAYOPEN

Not implemented. (Mac OS, Win32, Plan9, RISC OS)

setservent STAYOPEN

Not implemented. (Plan9, Win32, RISC OS)

endpwent

Not implemented. (Mac OS, Win32)

endgrent

Not implemented. (Mac OS, Win32, VMS, RISC OS)

endhostent

Not implemented. (Mac OS, Win32)

endnetent

Not implemented. (Mac OS, Win32, Plan9)

endprotoent

Not implemented. (Mac OS, Win32, Plan9)

endservent

Not implemented. (Plan9, Win32)

getsockopt SOCKET,LEVEL,OPTNAME

Not implemented. (Mac OS, Plan9)

glob EXPR
glob

Globbing built-in, but only * and ? metacharacters are supported. (Mac OS)

Features depend on external perlglob.exe or perlglob.bat. May be overridden with something like File::DosGlob, which is recommended. (Win32)

Globbing built-in, but only * and ? metacharacters are supported. Globbing relies on operating system calls, which may return filenames in any order. As most filesystems are case insensitive even "sorted" filenames will not be in case sensitive order. (RISC OS)

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 LIST

Not implemented, hence not useful for taint checking. (Mac OS, RISC OS)

Available only for process handles returned by the system(1, ...) method of spawning a process. (Win32)

Not implemented. (Mac OS, Win32, VMS, RISC OS)

lstat FILEHANDLE
lstat EXPR
lstat

Not implemented. (VMS, RISC OS)

Return values may be bogus. (Win32)

msgctl ID,CMD,ARG
msgget KEY,FLAGS
msgsnd ID,MSG,FLAGS
msgrcv ID,VAR,SIZE,TYPE,FLAGS

Not implemented. (Mac OS, Win32, VMS, Plan9, RISC OS)

open FILEHANDLE,EXPR
open FILEHANDLE

The | variants are only supported if ToolServer is installed. (Mac OS)

open to |- and -| are unsupported. (Mac OS, Win32, RISC OS)

Not implemented. (Mac OS)

Not implemented. (Win32, VMS, RISC OS)

select RBITS,WBITS,EBITS,TIMEOUT

Only implemented on sockets. (Win32)

Only reliable on sockets. (RISC OS)

semctl ID,SEMNUM,CMD,ARG
semget KEY,NSEMS,FLAGS
semop KEY,OPSTRING

Not implemented. (Mac OS, Win32, VMS, RISC OS)

setpgrp PID,PGRP

Not implemented. (Mac OS, Win32, VMS, RISC OS)

setpriority WHICH,WHO,PRIORITY

Not implemented. (Mac OS, Win32, VMS, RISC OS)

setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL

Not implemented. (Mac OS, Plan9)

shmctl ID,CMD,ARG
shmget KEY,SIZE,FLAGS
shmwrite ID,STRING,POS,SIZE

Not implemented. (Mac OS, Win32, VMS, RISC OS)

socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL

Not implemented. (Mac OS, Win32, VMS, RISC OS)

stat FILEHANDLE
stat EXPR
stat

mtime and atime are the same thing, and ctime is creation time instead of inode change time. (Mac OS)

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)

Not implemented. (Win32, VMS, RISC OS)

syscall LIST

Not implemented. (Mac OS, Win32, VMS, RISC OS)

sysopen FILEHANDLE,FILENAME,MODE,PERMS

The traditional "0", "1", and "2" MODEs are implemented with different numeric values on some systems. The flags exported by Fcntl should work everywhere though. (Mac OS, OS/390)

system LIST

Only implemented if ToolServer is installed. (Mac OS)

As an optimization, may not call the command shell specified in \$ENV{PERL5SHELL}. system(1, @args) spawns an external process and immediately returns its process designator, without waiting for it to terminate. Return value may be used subsequently in wait or waitpid. (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)

times

Only the first entry returned is nonzero. (Mac OS)

"cumulative" times will be bogus. On anything other than Windows NT, "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 FILEHANDLE,LENGTH
truncate EXPR,LENGTH

Not implemented. (VMS)

Returns undef where unavailable, as of version 5.005.

utime LIST

Only the modification time is updated. (Mac OS, VMS, RISC OS)

May not behave as expected. (Win32)

wait
waitpid PID,FLAGS

Not implemented. (Mac OS)

Can only be applied to process handles returned for processes spawned using system(1, ...). (Win32)

Not useful. (RISC OS)

# CHANGES

1.30, 03 August 1998

Major update for RISC OS, other minor changes.

1.23, 10 July 1998

First public release with perl5.005.

# AUTHORS / CONTRIBUTORS

Chris Nandor <pudge@pobox.com>, Gurusamy Sarathy <gsar@umich.edu>, Peter Prymmer <pvhp@forte.com>, Tom Christiansen <tchrist@perl.com>, Nathan Torkington <gnat@frii.com>, Paul Moore <Paul.Moore@uk.origin-it.com>, Matthias Neercher <neeri@iis.ee.ethz.ch>, Charles Bailey <bailey@genetics.upenn.edu>, Luther Huffman <lutherh@stratcom.com>, Gary Ng <71564.1743@CompuServe.COM>, Nick Ing-Simmons <nick@ni-s.u-net.com>, Paul J. Schinder <schinder@pobox.com>, Tom Phoenix <rootbeer@teleport.com>, Hugo van der Sanden <h.sanden@elsevier.nl>, Dominic Dunlop <domo@vo.lu>, Dan Sugalski <sugalskd@ous.edu>, Andreas J. Koenig <koenig@kulturbox.de>, Andrew M. Langmead <aml@world.std.com>, Andy Dougherty <doughera@lafcol.lafayette.edu>, Abigail <abigail@fnx.com>, Nicholas Clark <Nicholas.Clark@liverpool.ac.uk>.

This document is maintained by Chris Nandor.