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, 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
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:
   - 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
   - one of the directories in C<@INC>, or
   - a directory which the extensions Perl library module
     passes to the DynaLoader when asking it to map
     the shareable image, or
   - F<Sys$Share> or F<Sys$Library>.
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.

Filenames are, of course, still case-insensitive.  For
consistency, most Perl routines return  filespecs using
lower case letters only, regardless of the case used in
the arguments passed to them.  (This is true  only when
running under VMS; Perl respects the case-sensitivity
of OSs like Unix.)

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. 

=head2 Wildcard expansion

File specifications containing wildcards are allowed both on 
the command line and within Perl globs (e.g. <CE<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.

In both cases, VMS wildcard expansion is performed. (csh-style
wildcard expansion is available if you use C<File::Glob::glob>.)
If the wildcard filespec contains a device or directory 
specification, then the resultant filespecs will also contain 
a device and directory; otherwise, device and directory 
information are removed.  VMS-style resultant filespecs will 
contain a full device and directory, while Unix-style 
resultant filespecs will contain only as much of a directory 
path as was present in the input filespec.  For example, if 
your default directory is Perl_Root:[000000], the expansion 
of C<[.t]*.*> will yield filespecs  like 
"perl_root:[t]base.dir", while the expansion of C<t/*/*> will 
yield filespecs like "t/base.dir".  (This is done to match 
the behavior of glob expansion performed by Unix shells.) 

Similarly, the resultant filespec will contain the file version
only if one was present in the input filespec.

=head2 Pipes

Input and output pipes to Perl filehandles are supported; the 
"file name" is passed to lib$spawn() for asynchronous 
execution.  You should be careful to close any pipes you have 
opened in a Perl script, lest you leave any "orphaned" 
subprocesses around when Perl exits. 

You may also use backticks to invoke a DCL subprocess, whose 
output is used as the return value of the expression.  The 
string between the backticks is handled as if it were the
argument to the C<system> operator (see below).  In this case,
Perl will wait for the subprocess to complete before continuing. 

=head1 PERL5LIB and PERLLIB

The PERL5LIB and PERLLIB logical names work as documented in L<perl>,
except that the element separator is '|' instead of ':'.  The
directory specifications may use either VMS or Unix syntax.

=head1 Command line

=head2 I/O redirection and backgrounding

Perl for VMS supports redirection of input and output on the 
command line, using a subset of Bourne shell syntax:

    <F<file> reads stdin from F<file>,
    >F<file> writes stdout to F<file>,
    >>F<file> appends stdout to F<file>,
    2>F<file> writes stderr to F<file>, and
    2>>F<file> appends stderr to F<file>. 

In addition, output may be piped to a subprocess, using the  
character '|'.  Anything after this character on the command 
line is passed to a subprocess for execution; the subprocess 
takes the output of Perl as its input.

Finally, if the command line ends with '&', the entire 
command is run in the background as an asynchronous 
subprocess.

=head2 Command line switches

The following command line switches behave differently under
VMS than described in L<perlrun>.  Note also that in order
to pass uppercase switches to Perl, you need to enclose
them in double-quotes on the command line, since the CRTL
downcases all unquoted strings.

=over 4

=item -i

If the C<-i> switch is present but no extension for a backup
copy is given, then inplace editing creates a new version of
a file; the existing copy is not deleted.  (Note that if
an extension is given, an existing file is renamed to the backup
file, as is the case under other operating systems, so it does
not remain as a previous version under the original filename.)

=item -S

If the C<-S> switch is present I<and> the script name does
not contain a directory, then Perl translates the logical
name DCL$PATH as a searchlist, using each translation as
a directory in which to look for the script.  In addition,
if no file type is specified, Perl looks in each directory
for a file matching the name specified, with a blank type,
a type of F<.pl>, and a type of F<.com>, in that order.

=item -u

The C<-u> switch causes the VMS debugger to be invoked
after the Perl program is compiled, but before it has
run.  It does not create a core dump file.