perlvms.pod

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=head1 NAME

perlvms - VMS-specific documentation for Perl

=head1 DESCRIPTION

Gathered below are notes describing details of Perl 5's 
behavior on VMS.  They are a supplement to the regular Perl 5 
documentation, so we have focussed on the ways in which Perl 
5 functions differently under VMS than it does under Unix, 
and on the interactions between Perl and the rest of the 
operating system.  We haven't tried to duplicate complete 
descriptions of Perl features from the main Perl 
documentation, which can be found in the F<[.pod]> 
subdirectory of the Perl distribution.

We hope these notes will save you from confusion and lost 
sleep when writing Perl scripts on VMS.  If you find we've 
missed something you think should appear here, please don't 
hesitate to drop a line to [e-mail].

=head1 Installation

Directions for building and installing Perl 5 can be found in 
the file F<README.vms> in the main source directory of the 
Perl distribution..

=head1 Organization of Perl Images

=head2 Core Images

During the installation process, three Perl images are produced.
F<Miniperl.Exe> is an executable image which contains all of
the basic functionality of Perl, but cannot take advantage of
Perl extensions.  It is used to generate several files needed
to build the complete Perl and various extensions.  Once you've
finished installing Perl, you can delete this image.

Most of the complete Perl resides in the shareable image
F<PerlShr.Exe>, which provides a core to which the Perl executable
image and all Perl extensions are linked.  You should place this
image in F<Sys$Share>, or define the logical name F<PerlShr> to
translate to the full file specification of this image.  It should
be world readable.  (Remember that if a user has execute only access
to F<PerlShr>, VMS will treat it as if it were a privileged shareable
image, and will therefore require all downstream shareable images to be
INSTALLed, etc.)


Finally, F<Perl.Exe> is an executable image containing the main
entry point for Perl, as well as some initialization code.  It
should be placed in a public directory, and made world executable.
In order to run Perl with command line arguments, you should
define a foreign command to invoke this image.

=head2 Perl Extensions

Perl extensions are packages which provide both XS and Perl code
to add new functionality to perl.  (XS is a meta-language which
simplifies writing C code which interacts with Perl, see
L<perlxs> for more details.)  The Perl code for an
extension is treated like any other library module - it's
made available in your script through the appropriate
C<use> or C<require> statement, and usually defines a Perl
package containing the extension.

The portion of the extension provided by the XS code may be
connected to the rest of Perl in either of two ways.  In the
B<static> configuration, the object code for the extension is
linked directly into F<PerlShr.Exe>, and is initialized whenever
Perl is invoked.  In the B<dynamic> configuration, the extension's
machine code is placed into a separate shareable image, which is
mapped by Perl's DynaLoader when the extension is C<use>d or
C<require>d in your script.  This allows you to maintain the
extension as a separate entity, at the cost of keeping track of the
additional shareable image.  Most extensions can be set up as either
static or dynamic.

The source code for an extension usually resides in its own
directory.  At least three files are generally provided:
I<Extshortname>F<.xs> (where I<Extshortname> is the portion of
the extension's name following the last C<::>), containing
the XS code, I<Extshortname>F<.pm>, the Perl library module
for the extension, and F<Makefile.PL>, a Perl script which uses
the C<MakeMaker> library modules supplied with Perl to generate
a F<Descrip.MMS> file for the extension.

=head2 Installing static extensions

Since static extensions are incorporated directly into
F<PerlShr.Exe>, you'll have to rebuild Perl to incorporate a
new extension.  You should edit the main F<Descrip.MMS> or F<Makefile>
you use to build Perl, adding the extension's name to the C<ext>
macro, and the extension's object file to the C<extobj> macro.
You'll also need to build the extension's object file, either
by adding dependencies to the main F<Descrip.MMS>, or using a
separate F<Descrip.MMS> for the extension.  Then, rebuild
F<PerlShr.Exe> to incorporate the new code.

Finally, you'll need to copy the extension's Perl library
module to the F<[.>I<Extname>F<]> subdirectory under one
of the directories in C<@INC>, where I<Extname> is the name
of the extension, with all C<::> replaced by C<.> (e.g.
the library module for extension Foo::Bar would be copied
to a F<[.Foo.Bar]> subdirectory).

=head2 Installing dynamic extensions

In general, the distributed kit for a Perl extension includes
a file named Makefile.PL, which is a Perl program which is used
to create a F<Descrip.MMS> file which can be used to build and
install the files required by the extension.  The kit should be
unpacked into a directory tree B<not> under the main Perl source
directory, and the procedure for building the extension is simply

    $ perl Makefile.PL  ! Create Descrip.MMS
    $ mmk               ! Build necessary files
    $ mmk test          ! Run test code, if supplied
    $ mmk install       ! Install into public Perl tree

I<N.B.> The procedure by which extensions are built and
tested creates several levels (at least 4) under the
directory in which the extension's source files live.
For this reason if you are running a version of VMS prior
to V7.1 you shouldn't nest the source directory
too deeply in your directory structure lest you exceed RMS'
maximum of 8 levels of subdirectory in a filespec.  (You
can use rooted logical names to get another 8 levels of
nesting, if you can't place the files near the top of
the physical directory structure.)

VMS support for this process in the current release of Perl
is sufficient to handle most extensions.  However, it does
not yet recognize extra libraries required to build shareable
images which are part of an extension, so these must be added
to the linker options file for the extension by hand.  For
instance, if the F<PGPLOT> extension to Perl requires the
F<PGPLOTSHR.EXE> shareable image in order to properly link
the Perl extension, then the line C<PGPLOTSHR/Share> must
be added to the linker options file F<PGPLOT.Opt> produced
during the build process for the Perl extension.

By default, the shareable image for an extension is placed in
the F<[.lib.site_perl.auto>I<Arch>.I<Extname>F<]> directory of the
installed Perl directory tree (where I<Arch> is F<VMS_VAX> or
F<VMS_AXP>, and I<Extname> is the name of the extension, with
each C<::> translated to C<.>).  (See the MakeMaker documentation
for more details on installation options for extensions.)
However, it can be manually placed in any of several locations:

=over 4

=item *

the F<[.Lib.Auto.>I<Arch>I<$PVers>I<Extname>F<]> subdirectory
of one of the directories in C<@INC> (where I<PVers>
is the version of Perl you're using, as supplied in C<$]>,
with '.' converted to '_'), or

=item *

one of the directories in C<@INC>, or

=item *

a directory which the extensions Perl library module
passes to the DynaLoader when asking it to map
the shareable image, or

=item *

F<Sys$Share> or F<Sys$Library>.

=back

If the shareable image isn't in any of these places, you'll need
to define a logical name I<Extshortname>, where I<Extshortname>
is the portion of the extension's name after the last C<::>, which
translates to the full file specification of the shareable image.

=head1 File specifications

=head2 Syntax

We have tried to make Perl aware of both VMS-style and Unix-style file
specifications wherever possible.  You may use either style, or both,
on the command line and in scripts, but you may not combine the two
styles within a single file specification.  VMS Perl interprets Unix
pathnames in much the same way as the CRTL (I<e.g.> the first component
of an absolute path is read as the device name for the VMS file
specification).  There are a set of functions provided in the
C<VMS::Filespec> package for explicit interconversion between VMS and
Unix syntax; its documentation provides more details.

We've tried to minimize the dependence of Perl library
modules on Unix syntax, but you may find that some of these,
as well as some scripts written for Unix systems, will
require that you use Unix syntax, since they will assume that
'/' is the directory separator, I<etc.>  If you find instances
of this in the Perl distribution itself, please let us know,
so we can try to work around them.

Also when working on Perl programs on VMS, if you need a syntax
in a specific operating system format, then you need either to
check the appropriate DECC$ feature logical, or call a conversion
routine to force it to that format.

The feature logical name DECC$FILENAME_UNIX_REPORT modifies traditional
Perl behavior in the conversion of file specifications from UNIX to VMS
format in order to follow the extended character handling rules now
expected by the CRTL.  Specifically, when this feature is in effect, the
C<./.../> in a UNIX path is now translated to C<[.^.^.^.]> instead of
the traditional VMS C<[...]>.  To be compatible with what MakeMaker
expects, if a VMS path cannot be translated to a UNIX path, it is
passed through unchanged, so C<unixify("[...]")> will return C<[...]>.

The handling of extended characters is largely complete in the
VMS-specific C infrastructure of Perl, but more work is still needed to
fully support extended syntax filenames in several core modules.  In
particular, at this writing PathTools has only partial support for
directories containing some extended characters.

There are several ambiguous cases where a conversion routine cannot
determine whether an input filename is in UNIX format or in VMS format,
since now both VMS and UNIX file specifications may have characters in
them that could be mistaken for syntax delimiters of the other type. So
some pathnames simply cannot be used in a mode that allows either type
of pathname to be present.  Perl will tend to assume that an ambiguous
filename is in UNIX format.

Allowing "." as a version delimiter is simply incompatible with
determining whether a pathname is in VMS format or in UNIX format with
extended file syntax.  There is no way to know whether "perl-5.8.6" is a
UNIX "perl-5.8.6" or a VMS "perl-5.8;6" when passing it to unixify() or
vmsify().

The DECC$FILENAME_UNIX_REPORT logical name controls how Perl interprets
filenames to the extent that Perl uses the CRTL internally for many
purposes, and attempts to follow CRTL conventions for reporting
filenames.  The DECC$FILENAME_UNIX_ONLY feature differs in that it
expects all filenames passed to the C run-time to be already in UNIX
format.  This feature is not yet supported in Perl since Perl uses
traditional OpenVMS file specifications internally and in the test
harness, and it is not yet clear whether this mode will be useful or
useable.  The feature logical name DECC$POSIX_COMPLIANT_PATHNAMES is new
with the RMS Symbolic Link SDK and included with OpenVMS v8.3, but is
not yet supported in Perl.

=head2 Filename Case

Perl follows VMS defaults and override settings in preserving (or not
preserving) filename case.  Case is not preserved on ODS-2 formatted
volumes on any architecture.  On ODS-5 volumes, filenames may be case
preserved depending on process and feature settings.  Perl now honors
DECC$EFS_CASE_PRESERVE and DECC$ARGV_PARSE_STYLE on those systems where
the CRTL supports these features.  When these features are not enabled
or the CRTL does not support them, Perl follows the traditional CRTL
behavior of downcasing command-line arguments and returning file
specifications in lower case only.

I<N. B.>  It is very easy to get tripped up using a mixture of other
programs, external utilities, and Perl scripts that are in varying
states of being able to handle case preservation.  For example, a file
created by an older version of an archive utility or a build utility
such as MMK or MMS may generate a filename in all upper case even on an
ODS-5 volume.  If this filename is later retrieved by a Perl script or
module in a case preserving environment, that upper case name may not
match the mixed-case or lower-case expections of the Perl code.  Your
best bet is to follow an all-or-nothing approach to case preservation:
either don't use it at all, or make sure your entire toolchain and
application environment support and use it.

OpenVMS Alpha v7.3-1 and later and all version of OpenVMS I64 support
case sensitivity as a process setting (see C<SET PROCESS
/CASE_LOOKUP=SENSITIVE>). Perl does not currently suppport case
sensitivity on VMS, but it may in the future, so Perl programs should
use the C<File::Spec->case_tolerant> method to determine the state, and
not the C<$^O> variable.

=head2 Symbolic Links

When built on an ODS-5 volume with symbolic links enabled, Perl by
default supports symbolic links when the requisite support is available
in the filesystem and CRTL (generally 64-bit OpenVMS v8.3 and later). 
There are a number of limitations and caveats to be aware of when
working with symbolic links on VMS.  Most notably, the target of a valid
symbolic link must be expressed as a UNIX-style path and it must exist
on a volume visible from your POSIX root (see the C<SHOW ROOT> command
in DCL help).  For further details on symbolic link capabilities and
requirements, see chapter 12 of the CRTL manual that ships with OpenVMS
v8.3 or later.

=head2 Wildcard expansion

File specifications containing wildcards are allowed both on 
the command line and within Perl globs (e.g. C<E<lt>*.cE<gt>>).  If
the wildcard filespec uses VMS syntax, the resultant 
filespecs will follow VMS syntax; if a Unix-style filespec is 
passed in, Unix-style filespecs will be returned.
Similar to the behavior of wildcard globbing for a Unix shell,
one can escape command line wildcards with double quotation
marks C<"> around a perl program command line argument.  However,
owing to the stripping of C<"> characters carried out by the C
handling of argv you will need to escape a construct such as
this one (in a directory containing the files F<PERL.C>, F<PERL.EXE>,
F<PERL.H>, and F<PERL.OBJ>):