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=head1 Notes on Perl 5 for VMS

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 vmsperl@genetics.upenn.edu.

=head1 Organization of Perl

=head2 Perl 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<perlapi> 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.

=head3 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).

=head3 Installic dynamic extensions

First, you'll need to compile the XS code into a shareable image,
either by hand or using the F<Descrip.MMS> supplied with the
extension.  If you're building the shareable image by hand, please
note the following points:
    - The shareable image must be linked to F<PerlShr.Exe>, so it
      has access to Perl's global variables and routines.  In
      order to specify the correct attributes for psects in
      F<PerlShr.Exe>, you should include the linker options file
      F<PerlShr_Attr.Opt> in the Link command.  (This file is
      generated when F<PerlShr.Exe> is built, and is found in the
      main Perl source directory.
    - The entry point for the C<boot_>I<Extname> routine (where
      I<Extname> is the name of the extension, with all C<::>
      replaced by C<__>) must be a universal symbol.  No other
      universal symbols are required to use the shareable image
      with Perl, though you may want to include additional
      universal symbols if you plan to share code or data among
      different extensions.
The shareable image can be placed in any of several locations:
   - the F<[.Auto.>I<Extname>F<]> subdirectory of one of
     the directories in C<@INC>, where I<Extname> is the
     name of the extension, with each C<::> translated to C<.>
     (e.g. for extension Foo::Bar, you would use the
     F<[.Auto.Foo.Bar]> subdirectory), 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.

Once you've got the shareable image set up, you should copy the
extension's Perl library module to the appropriate library directory
(see the section above on installing static extensions).

=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 File specifications 

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 fle 
specfication.  Filenames are, of course, still case-
insensitive.  For consistency, most Perl routines return 
filespecs using lower case latters 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, etc.  If you find instances 
of this in the Perl distribution itself, please let us know, 
so we can try to work around them. 

=head1 Command line redirection

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.

=head1 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 passed directly to lib$spawn 
as the command to execute.  In this case, Perl will wait for 
the subprocess to complete before continuing. 

=head1 Wildcard expansion

File specifications containing wildcards are allowed both on 
the command line and within Perl globs (e.g. <C<*.c>>).  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..

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 the file version only 
if one was present in the input filespec.

=head1 PERL5LIB and PERLLIB

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

=head1 %ENV 

Reading the elements of the %ENV array returns the 
translation of the logical name specified by the key, 
according to the normal search order of access modes and 
logical name tables.  In addition, the keys C<home>, 
C<path>,C<term>, and C<user> return the CRTL "environment 
variables" of the same names.  The key C<default> returns the 
current default device and directory specification.

Setting an element of %ENV defines a supervisor-mode logical 
name in the process logical name table.  C<Undef>ing or 
C<delete>ing an element of %ENV deletes the equivalent user-
mode or supervisor-mode logical name from the process logical 
name table.  If you use C<undef>, the %ENV element remains 
empty.  If you use C<delete>, another attempt is made at 
logical name translation after the deletion, so an inner-mode 
logical name or a name in another logical name table will 
replace the logical name just deleted.

In all operations on %ENV, the key string is treated as if it 
were entirely uppercase, regardless of the case actually 
specified in the Perl expression.

=head1 Perl functions

As of the time this document was last revised, the following 
Perl functions were implemented in the VMS port of Perl 
(functions marked with * are discussed in more detail below):

    file tests*, abs, alarm, atan, binmode*, bless,
    caller, chdir, chmod, chown, chomp, chop, chr,
    close, closedir, cos, defined, delete, die, do,
    each, endpwent, eof, eval, exec*, exists, exit,
    exp, fileno, fork*, getc, getpwent*, getpwnam*,
    getpwuid*, glob, goto, grep, hex, import, index,
    int, join, keys, kill, last, lc, lcfirst, length,
    local, localtime, log, m//, map, mkdir, my, next,
    no, oct, open, opendir, ord, pack, pipe, pop, pos,
    print, printf, push, q//, qq//, qw//, qx//,
    quotemeta, rand, read, readdir, redo, ref, rename,
    require, reset, return, reverse, rewinddir, rindex,
    rmdir, s///, scalar, seek, seekdir, select(internal)*,
    setpwent, shift, sin, sleep, sort, splice, split,
    sprintf, sqrt, srand, stat, study, substr, sysread,
    system*, syswrite, tell, telldir, tie, time, times*,
    tr///, uc, ucfirst, umask, undef, unlink*, unpack,
    untie, unshift, use, utime*, values, vec, wait,
    waitpid*, wantarray, warn, write, y///

The following functions were not implemented in the VMS port, 
and calling them produces a fatal error (usually) or 
undefined behavior (rarely, we hope):

    chroot, crypt, dbmclose, dbmopen, dump, fcntl,
    flock, getlogin, getpgrp, getppid, getpriority,
    getgrent, kill, getgrgid, getgrnam, setgrent,
    endgrent, gmtime, ioctl, link, lstst, msgctl,
    msgget, msgsend, msgrcv, readlink,
    select(system call), semctl, semget, semop,
    setpgrp, setpriority, shmctl, shmget, shmread,
    shmwrite, socketpair, symlink, syscall, truncate

The following functions may or may not be implemented, 
depending on what type of socket support you've built into 
your copy of Perl:
    accept, bind, connect, getpeername,
    gethostbyname, getnetbyname, getprotobyname,
    getservbyname, gethostbyaddr, getnetbyaddr,
    getprotobynumber, getservbyport, gethostent,
    getnetent, getprotoent, getservent, sethostent,
    setnetent, setprotoent, setservent, endhostent,
    endnetent, endprotoent, endservent, getsockname,
    getsockopt, listen, recv, send, setsockopt,
    shutdown, socket


=item File tests

The tests C<-b>, C<-B>, C<-c>, C<-C>, C<-d>, C<-e>, C<-f>,
C<-o>, C<-M>, C<-s>, C<-S>, C<-t>, C<-T>, and C<-z> work as
advertised.  The return values for C<-r>, C<-w>, and C<-x>
tell you whether you can actually access the file; this may
not reflect the UIC-based file protections.  Since real and
effective UIC don't differ under VMS, C<-O>, C<-R>, C<-W>,
and C<-X> are equivalent to C<-o>, C<-r>, C<-w>, and C<-x>.
Similarly, several other tests, including C<-A>, C<-g>, C<-k>,
C<-l>, C<-p>, and C<-u>, aren't particularly meaningful under
VMS, and the values returned by these tests reflect whatever
your CRTL C<stat()> routine does to the equivalent bits in the
st_mode field.  Finally, C<-d> returns true if passed a device
specification without an explicit directory (e.g. C<DUA1:>), as
well as if passed a directory.

=item binmode FILEHANDLE

The C<binmode> operator has no effect under VMS.  It will 
return TRUE whenever called, but will not affect I/O 
operations on the filehandle given as its argument.

=item exec LIST

The C<exec> operator behaves in one of two different ways.  
If called after a call to C<fork>, it will invoke the CRTL 
C<execv()> routine, passing its arguments to the subprocess 
created by C<fork> for execution.  In this case, it is 
subject to all limitations that affect C<execv()>.  (In 
particular, this usually means that the command executed in 
the subprocess must be an image compiled from C source code, 
and that your options for passing file descriptors and signal 
handlers to the subprocess are limited.)

If the call to C<exec> does not follow a call to C<fork>, it 
will cause Perl to exit, and to invoke the command given as 
an argument to C<exec> via C<lib$do_command>.  If the argument 
begins with a '$' (other than as part of a filespec), then it 
is executed as a DCL command.  Otherwise, the first token on 
the command line is treated as the filespec of an image to 
run, and an attempt is made to invoke it (using F<.Exe> and 
the process defaults to expand the filespec) and pass the 
rest of C<exec>'s argument to it as parameters.

You can use C<exec> in both ways within the same script, as 
long as you call C<fork> and C<exec> in pairs.  Perl
keeps track of how many times C<fork> and C<exec> have been
called, and will call the CRTL C<execv()> routine if there have
previously been more calls to C<fork> than to C<exec>.

=item fork

The C<fork> operator works in the same way as the CRTL 
C<vfork()> routine, which is quite different under VMS than 
under Unix.  Specifically, while C<fork> returns 0 after it 
is called and the subprocess PID after C<exec> is called, in 
both cases the thread of execution is within the parent 
process, so there is no opportunity to perform operations in 
the subprocess before calling C<exec>.

In general, the use of C<fork> and C<exec> to create 
subprocess is not recommended under VMS; wherever possible, 
use the C<system> operator or piped filehandles instead.

=item getpwent
=item getpwnam
=item getpwuid

These operators obtain the information described in L<perlfunc>,
if you have the privileges necessary to retrieve the named user's
UAF information via C<sys$getuai>.  If not, then only the C<$name>,
C<$uid>, and C<$gid> items are returned.  The C<$dir> item contains
the login directory in VMS syntax, while the C<$comment> item
contains the login directory in Unix syntax. The C<$gcos> item
contains the owner field from the UAF record.  The C<$quota>
item is not used.

=item stat EXPR

Since VMS keeps track of files according to a different scheme
than Unix, it's not really possible to represent the file's ID
in the C<st_dev> and C<st_ino> fields of a C<struct stat>.  Perl
tries its best, though, and the values it uses are pretty unlikely
to be the same for two different files.  We can't guarantee this,
though, so caveat scriptor.

=item system LIST

The C<system> operator creates a subprocess, and passes its 
arguments to the subprocess for execution as a DCL command.  
Since the subprocess is created directly via lib$spawn, any 
valid DCL command string may be specified.  If LIST consists
of the empty string, C<system> spawns an interactive DCL subprocess,
in the same fashion as typiing B<SPAWN> at the DCL prompt.
Perl waits for the subprocess to complete before continuing
execution in the current process.

=item times

The array returned by the C<times> operator is divided up 
according to the same rules the CRTL C<times()> routine.  
Therefore, the "system time" elements will always be 0, since 
there is no difference between "user time" and "system" time 
under VMS, and the time accumulated by subprocess may or may 
not appear separately in the "child time" field, depending on 
whether L<times> keeps track of subprocesses separately.  Note
especially that the VAXCRTL (at least) keeps track only of
subprocesses spawned using L<fork> and L<exec>; it will not
accumulate the times of suprocesses spawned via pipes, L<system>,
or backticks.

=item unlink LIST

C<unlink> will delete the highest version of a file only; in
order to delete all versions, you need to say
    1 while (unlink LIST);
You may need to make this change to scripts written for a
Unix system which expect that after a call to C<unlink>,
no files with the names passed to C<unlink> will exist.
(Note: This can be changed at compile time; if you
C<use Config> and C<$Config{'d_unlink_all_versions'}> is
C<define>, then C<unlink> will delete all versions of a
file on the first call.)

C<unlink> will delete a file if at all possible, even if it
requires changing file protection (though it won't try to
change the protection of the parent directory).  You can tell
whether you've got explicit delete access to a file by using the
C<VMS::Filespec::candelete> operator.  For instance, in order
to delete only files to which you have delete access, you could
say something like
    sub safe_unlink {
        my($file,$num);
        foreach $file (@_) {
            next unless VMS::Filespec::candelete($file);
            $num += unlink $file;
        }
        $num;
    }
Finally, if C<unlink> has to change the file protection to
delete the file, and you interrupt it in midstream, the file
may be left intact, but with a changed ACL allowing you delete
access.

=item utime LIST

Since ODS-2, the VMS file structure for disk files, does not keep
track of access times, this operator changes only the modification
time of the file (VMS revision date).

=item waitpid PID,FLAGS

If PID is a subprocess started by a piped L<open>, C<waitpid>
will wait for that subprocess, and return its final
status value.  If PID is a subprocess created in some other way
(e.g. SPAWNed before Perl was invoked), or is not a subprocess of
the current process, C<waitpid> will check once per second whether
the process has completed, and when it has, will return 0.  (If PID
specifies a process that isn't a subprocess of the current process,
and you invoked Perl with the C<-w> switch, a warning will be issued.)

The FLAGS argument is ignored in all cases.

=head1 Revision date

This document was last updated on 16-Dec-1994, for Perl 5, 
patchlevel 0.