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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
    Darwin        darwin     darwin
    dgux          dgux       AViiON-dgux
    DYNIX/ptx     dynixptx   i386-dynixptx
    FreeBSD       freebsd    freebsd-i386    
    Linux         linux      arm-linux
    Linux         linux      i386-linux
    Linux         linux      i586-linux
    Linux         linux      ppc-linux
    HP-UX         hpux       PA-RISC1.1
    IRIX          irix       irix
    Mac OS X      darwin     darwin
    MachTen PPC   machten    powerpc-machten
    NeXT 3        next       next-fat
    NeXT 4        next       OPENSTEP-Mach
    openbsd       openbsd    i386-openbsd
    OSF1          dec_osf    alpha-dec_osf
    reliantunix-n svr4       RM400-svr4
    SCO_SV        sco_sv     i386-sco_sv
    SINIX-N       svr4       RM400-svr4
    sn4609        unicos     CRAY_C90-unicos
    sn6521        unicosmk   t3e-unicosmk
    sn9617        unicos     CRAY_J90-unicos
    SunOS         solaris    sun4-solaris
    SunOS         solaris    i86pc-solaris
    SunOS4        sunos      sun4-sunos  

Because the value of $Config{archname} may depend on the hardware architecture, it can vary more than the value of $^O.

DOS and Derivatives

Perl has long been ported to Intel-style microcomputers running under systems like PC-DOS, MS-DOS, OS/2, and most Windows platforms you can bring yourself to mention (except for Windows CE, if you count that). Users familiar with COMMAND.COM or CMD.EXE style shells should be aware that each of these file specifications may have subtle differences:

    $filespec0 = "c:/foo/bar/file.txt";
    $filespec1 = "c:\\foo\\bar\\file.txt";
    $filespec2 = 'c:\foo\bar\file.txt';
    $filespec3 = 'c:\\foo\\bar\\file.txt';  

System calls accept either / or \ as the path separator. However, many command-line utilities of DOS vintage treat / as the option prefix, so may get confused by filenames containing /. Aside from calling any external programs, / will work just fine, and probably better, as it is more consistent with popular usage, and avoids the problem of remembering what to backwhack and what not to.

The DOS FAT filesystem can accommodate only "8.3" style filenames. Under the "case-insensitive, but case-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 xx
     Windows XP    MSWin32    MSWin32-x86       2      ?
     Windows CE    MSWin32    ?                 3           
     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, and perldos.
  • The EMX environment for DOS, OS/2, etc., or Also perlos2.
  • Build instructions for Win32 in perlwin32, or under the Cygnus environment in perlcygwin.
  • The Win32::* modules in Win32.
  • The ActiveState Pages,
  • The Cygwin environment for Win32; README.cygwin (installed as perlcygwin),
  • The U/WIN environment for Win32,
  • Build instructions for OS/2, perlos2

Mac OS

Any module requiring XS compilation is right out for most people, because MacPerl is built using non-free (and non-cheap!) compilers. Some XS modules that can work with MacPerl are built and distributed in binary form on CPAN.

Directories are specified as:

    volume:folder:file              for absolute pathnames
    volume:folder:                  for absolute pathnames
    :folder:file                    for relative pathnames
    :folder:                        for relative pathnames
    :file                           for relative pathnames
    file                            for relative pathnames  

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

Instead of flock, see FSpSetFLock and FSpRstFLock in the Mac::Files module, or chmod(0444, ...) and chmod(0666, ...).

In the MacPerl application, you can't run a program from the command line; programs that expect @ARGV to be 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, based on NeXT's OpenStep OS, runs MacPerl natively, under the "Classic" environment. There is no "Carbon" version of MacPerl to run under the primary Mac OS X environment. Mac OS X and its Open Source version, Darwin, both run Unix perl natively.

Also see:

  • MacPerl Development, .
  • The MacPerl Pages, .
  • The MacPerl mailing lists, .


Perl on VMS is discussed in perlvms in the perl distribution. Perl on VMS can accept either VMS- or Unix-style file specifications as in either of the following:

    $ perl -ne "print if /perl_setup/i" SYS$LOGIN:LOGIN.COM
    $ perl -ne "print if /perl_setup/i" /sys$login/  

but not a mixture of both as in:

    $ perl -ne "print if /perl_setup/i" sys$login:/
    Can't open sys$login:/ 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__"

    print "Hello from Perl!\n";

    $ endif  

Do take care with $ ASSIGN/nolog/user SYS$COMMAND: SYS$INPUT if your perl-in-DCL script expects to do things like $read = <STDIN>;.

Filenames are in the format "name.extension;version". The maximum length for filenames is 39 characters, and the maximum length for extensions is also 39 characters. Version is a number from 1 to 32767. Valid characters are /[A-Z0-9$_-]/.

VMS's RMS filesystem is case-insensitive and does not preserve case. readdir returns lowercased filenames, but specifying a file for opening remains case-insensitive. Files without extensions have a trailing period on them, so doing a readdir with a file named A.;5 will return a. (though that file could be opened with open(FH, 'A')).

RMS had an eight level limit on directory depths from any rooted logical (allowing 16 levels overall) prior to VMS 7.2. Hence PERL_ROOT:[LIB.] is a valid directory specification but PERL_ROOT:[LIB.] is not. Makefile.PL authors might have to take this into account, but at least they can refer to the former as /PERL_ROOT/lib/2/3/4/5/6/7/8/.

The VMS::Filespec module, which gets installed as part of the build process on VMS, is a pure Perl module that can easily be installed on non-VMS platforms and can be helpful for conversions to and from RMS native formats.

What \n represents depends on the type of file opened. It usually represents \012 but it could also be \015, \012, \015\012, \000, \040, or nothing depending on the file organiztion and record format. The VMS::Stdio module provides access to the special fopen() requirements of files with unusual attributes on VMS.

TCP/IP stacks are optional on VMS, so socket routines might not be implemented. UDP sockets may not be supported.

The value of $^O on OpenVMS is "VMS". To determine the architecture that you are running on without resorting to loading all of %Config you can examine the content of the @INC array like so:

    if (grep(/VMS_AXP/, @INC)) {
        print "I'm on Alpha!\n";

    } elsif (grep(/VMS_VAX/, @INC)) {
        print "I'm on VAX!\n";

    } else {
        print "I'm not so sure about where $^O is...\n";

On VMS, perl determines the UTC offset from the SYS$TIMEZONE_DIFFERENTIAL logical name. Although the VMS epoch began at 17-NOV-1858 00:00:00.00, calls to localtime are adjusted to count offsets from 01-JAN-1970 00:00:00.00, just like Unix.

Also see:

  • README.vms (installed as README_vms), perlvms
  • vmsperl list,

    (Put the words subscribe vmsperl in message body.)

  • vmsperl on the web,


Perl on VOS is discussed in README.vos in the perl distribution (installed as perlvos). Perl on VOS can accept either VOS- or Unix-style file specifications as in either of the following:

    C<< $ perl -ne "print if /perl_setup/i" >system>notices >>
    C<< $ perl -ne "print if /perl_setup/i" /system/notices >>  

or even a mixture of both as in:

    C<< $ perl -ne "print if /perl_setup/i" >system/notices >>  

Even though VOS allows the slash character to appear in object names, because the VOS port of Perl interprets it as a pathname delimiting character, VOS files, directories, or links whose names contain a slash character cannot be processed. Such files must be renamed before they can be processed by Perl. Note that VOS limits file names to 32 or fewer characters.

Perl on VOS can be built using two different compilers and two different versions of the POSIX runtime. The recommended method for building full Perl is with the GNU C compiler and the generally-available version of VOS POSIX support. See README.vos (installed as perlvos) for restrictions that apply when Perl is built using the VOS Standard C compiler or the alpha version of VOS POSIX support.

The value of $^O on VOS is "VOS". To determine the architecture that you are running on without resorting to loading all of %Config you can examine the content of the @INC array like so:

    if ($^O =~ /VOS/) {
        print "I'm on a Stratus box!\n";
    } else {
        print "I'm not on a Stratus box!\n";

    if (grep(/860/, @INC)) {
        print "This box is a Stratus XA/R!\n";

    } elsif (grep(/7100/, @INC)) {
        print "This box is a Stratus HP 7100 or 8xxx!\n";

    } elsif (grep(/8000/, @INC)) {
        print "This box is a Stratus HP 8xxx!\n";

    } else {
        print "This box is a Stratus 68K!\n";

Also see:

  • README.vos (installed as perlvos)
  • The VOS mailing list.

    There is no specific mailing list for Perl on VOS. You can post comments to the comp.sys.stratus newsgroup, or subscribe to the general Stratus mailing list. Send a letter with "subscribe Info-Stratus" in the message body to

  • VOS Perl on the web at

EBCDIC Platforms

Recent versions of Perl have been ported to platforms such as OS/400 on AS/400 minicomputers as well as OS/390, VM/ESA, and BS2000 for S/390 Mainframes. Such computers use EBCDIC character sets internally (usually Character Code Set ID 0037 for OS/400 and either 1047 or POSIX-BC for S/390 systems). On the mainframe perl currently works under the "Unix system services for OS/390" (formerly known as OpenEdition), VM/ESA OpenEdition, or the BS200 POSIX-BC system (BS2000 is supported in perl 5.6 and greater). See perlos390 for details.

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:

      CALL PGM(PERL5/PERL) PARM('/QOpenSys/')

This will invoke the perl script 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 & VM/ESA):

    print "Content-type: text/html\r\n\r\n";  

The values of $^O on some of these platforms includes:

    uname         $^O        $Config{'archname'}
    OS/390        os390      os390
    OS400         os400      os400
    POSIX-BC      posix-bc   BS2000-posix-bc
    VM/ESA        vmesa      vmesa  

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

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

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

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

One thing you may not want to rely on is the EBCDIC encoding of punctuation characters since these may differ from code page to code page (and once your module or script is rumoured to work with EBCDIC, folks will want it to work with all EBCDIC character sets).

Also see:

  • *

    perlos390, README.os390, perlbs2000, README.vmesa, perlebcdic.

  • The 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
  • AS/400 Perl information at as well as on CPAN in the ports/ directory.


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



    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:

    C:foo.h        (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, 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, Atari MiNT, BeOS, HP MPE/iX, QNX, Plan 9, and VOS, have been well-integrated into the standard Perl source code kit. You may need to see the ports/ directory on CPAN for information, and possibly binaries, for the likes of: aos, Atari ST, lynxos, riscos, Novell Netware, Tandem Guardian, etc. (Yes, we know that some of these OSes may fall under the Unix category, but we are not a standards body.)

Some approximate operating system names and their $^O values in the "OTHER" category include:

    OS            $^O        $Config{'archname'}
    Amiga DOS     amigaos    m68k-amigos
    BeOS          beos
    MPE/iX        mpeix      PA-RISC1.1  

See also:

  • Amiga, README.amiga (installed as perlamiga).
  • Atari, and Guido Flohr's web page
  • Be OS, README.beos
  • HP 300 MPE/iX, README.mpeix and Mark Bixby's web page
  • A free perl5-based PERL.NLM for Novell Netware is available in precompiled binary and source code form from as well as from CPAN.
  • Plan 9, README.plan9




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