path: root/vms/perlvms.pod

=head1 Notes on Perl5 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 thatn it does under Unix, 
and on teh interactions between perl and the rest of the 
operating system.  We haven't tried to duplicate complete 
descriptions  of perl5 features from the main perl 
documentation, which can be found in the F<[.pod]> 
subdirectory of the perl 5 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.

=head2 Installation

Directions for building and installing perl 5 can be found in 
the file F<ReadMe.VMS> in the main source directory of the 
perl5 distribution..

=head2 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 perl5 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; perl5 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. 

=head2 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> wrtits 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 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. 

=head2 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.

=head2 %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.  B<Undef>ing or 
B<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 B<undef>, the %ENV element remains 
empty.  If you use B<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.

=head2 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, eof, eval, exec*, exists, exit, exp, fileno,
    fork*, getc, 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)*,
    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, values, vec, wait, 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,
    getpwent, getgrent, kill, getgrgid, getgrnam,
    getpwnam, getpwuid, setpwent, setgrent,
    endpwent, 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,
    utime, waitpid

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 -b, -B, -c, -C, -d, -e, -f, -o, -M, -s, -S, -t, -T, 
and -z work as advertised.  The return values for -r, -w, and 
-x tell you whether you can actually access the file; this 
may mot reflect the UIC-based file protections.  Since real 
and effective UIC don't differ under VMS, -O, -R, -W, and -X 
are equivalent to -o, -r, -w, and -x.  Similarly, several 
other tests, including -A, -g, -k, -l,-p, and -u, aren't 
particularly meaningful under VMS, and the values returned by 
these tests reflect whatever your CRTL stat() routine does to 
the equivalent bits in the st_mode field.

=item binmode

The B<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 

The B<exec> operator behaves in one of two different ways.  
If called after a call to B<fork>, it will invoke the CRTL 
L<execv()> routine, passing its arguments to the subprocess 
created by B<fork> for execution.  In this case, it is 
subject to all limitation that affect L<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 B<exec> does not follow a call to B<fork>, it 
will cause perl to exit, and to invoke the command given as 
an argument to B<exec> via 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 B<exec>'s argument to it as parameters.

You can use B<exec> in both ways within the same script, as 
long as you call B<fork> and B<exec> in pairs.  Perl only 
keeps track of whether B<fork> has been called since the last 
call to B<exec> when figuring out what to do, so multiple 
calls to B<fork> do not generate multiple levels of "fork 
context".

=item fork

The B<fork> operator works in the same way as the CRTL 
L<fork()> routine, which is quite different under VMS than 
under Unix.  Sepcifically, while B<fork> returns 0 after it 
is called and the subprocess PID after B<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 B<exec>.

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

=item system

The B<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.  Perl waits for 
the subprocess to complete before continuing execution in the 
current process.

=item times

The array returned by the B<times> operator is divided up 
according to the same rules the CRTL L<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.

=head2 Revision date

This document was last updated on 16-Oct-1994, for perl 5, 
patchlevel 0.