NAME¶

perlvms - VMS-specific documentation for Perl

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 [.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@perl.org.

Installation¶

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

Organization of Perl Images¶

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

File specifications¶

    $ perl -e "print join(' ',@ARGV)" perl.*
    perl.c perl.exe perl.h perl.obj

    $ perl -e "print join(' ',@ARGV)" """perl.*"""
    perl.*

    $ Define PERL_MBX_SIZE 32767

PERL5LIB and PERLLIB¶

The PERL5LIB and PERLLIB environment elements work as documented in perl, except that the element separator is, by default, '|' instead of ':'. However, when running under a Unix shell as determined by the logical name "GNV$UNIX_SHELL", the separator will be ':' as on Unix systems. The directory specifications may use either VMS or Unix syntax.

The Perl Forked Debugger¶

The Perl forked debugger places the debugger commands and output in a separate X-11 terminal window so that commands and output from multiple processes are not mixed together.

Perl on VMS supports an emulation of the forked debugger when Perl is run on a VMS system that has X11 support installed.

To use the forked debugger, you need to have the default display set to an X-11 Server and some environment variables set that Unix expects.

The forked debugger requires the environment variable "TERM" to be "xterm", and the environment variable "DISPLAY" to exist. "xterm" must be in lower case.

  $define TERM "xterm"
  $define DISPLAY "hostname:0.0"

Currently the value of "DISPLAY" is ignored. It is recommended that it be set to be the hostname of the display, the server and screen in Unix notation. In the future the value of DISPLAY may be honored by Perl instead of using the default display.

It may be helpful to always use the forked debugger so that script I/O is separated from debugger I/O. You can force the debugger to be forked by assigning a value to the logical name <PERLDB_PIDS> that is not a process identification number.

  $define PERLDB_PIDS XXXX

PERL_VMS_EXCEPTION_DEBUG¶

The PERL_VMS_EXCEPTION_DEBUG being defined as "ENABLE" will cause the VMS debugger to be invoked if a fatal exception that is not otherwise handled is raised. The purpose of this is to allow debugging of internal Perl problems that would cause such a condition.

This allows the programmer to look at the execution stack and variables to find out the cause of the exception. As the debugger is being invoked as the Perl interpreter is about to do a fatal exit, continuing the execution in debug mode is usually not practical.

Starting Perl in the VMS debugger may change the program execution profile in a way that such problems are not reproduced.

The "kill" function can be used to test this functionality from within a program.

In typical VMS style, only the first letter of the value of this logical name is actually checked in a case insensitive mode, and it is considered enabled if it is the value "T","1" or "E".

This logical name must be defined before Perl is started.

Command line¶

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, backticks*, binmode*, bless,
    caller, chdir, chmod, chown, chomp, chop, chr,
    close, closedir, cos, crypt*, defined, delete, die, do, dump*, 
    each, endgrent, endpwent, eof, eval, exec*, exists, exit, exp, 
    fileno, flock  getc, getgrent*, getgrgid*, getgrnam, getlogin,
    getppid, getpwent*, getpwnam*, getpwuid*, glob, gmtime*, goto,
    grep, hex, ioctl, import, index, int, join, keys, kill*,
    last, lc, lcfirst, lchown*, length, link*, local, localtime, log,
    lstat, 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, readlink*, redo, ref,
    rename, require, reset, return, reverse, rewinddir, rindex,
    rmdir, s///, scalar, seek, seekdir, select(internal),
    select (system call)*, setgrent, setpwent, shift, sin, sleep,
    socketpair, sort, splice, split, sprintf, sqrt, srand, stat,
    study, substr, symlink*, 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, dbmclose, dbmopen, fork*, getpgrp, getpriority,  
    msgctl, msgget, msgsend, msgrcv, semctl,
    semget, semop, setpgrp, setpriority, shmctl, shmget,
    shmread, shmwrite, syscall

The following functions are available on Perls compiled with Dec C 5.2 or greater and running VMS 7.0 or greater:

    truncate

The following functions are available on Perls built on VMS 7.2 or greater:

    fcntl (without locking)

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, select(system call)*,
    send, setsockopt, shutdown, socket

The following function is available on Perls built on 64 bit OpenVMS v8.2 with hard links enabled on an ODS-5 formatted build disk. CRTL support is in principle available as of OpenVMS v7.3-1, and better configuration support could detect this.

    link

The following functions are available on Perls built on 64 bit OpenVMS v8.2 and later. CRTL support is in principle available as of OpenVMS v7.3-2, and better configuration support could detect this.

   getgrgid, getgrnam, getpwnam, getpwuid,
   setgrent, ttyname

The following functions are available on Perls built on 64 bit OpenVMS v8.2 and later.

   statvfs, socketpair

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 not 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. Finally, "-d" returns true if passed a device specification without an explicit directory (e.g. "DUA1:"), as well as if passed a directory.

There are DECC feature logical names AND ODS-5 volume attributes that also control what values are returned for the date fields.

Note: Some sites have reported problems when using the file-access tests ("-r", "-w", and "-x") on files accessed via DEC's DFS. Specifically, since DFS does not currently provide access to the extended file header of files on remote volumes, attempts to examine the ACL fail, and the file tests will return false, with $! indicating that the file does not exist. You can use "stat" on these files, since that checks UIC-based protection only, and then manually check the appropriate bits, as defined by your C compiler's stat.h, in the mode value it returns, if you need an approximation of the file's protections.

backticks

Backticks create a subprocess, and pass the enclosed string to it for execution as a DCL command. Since the subprocess is created directly via "lib$spawn()", any valid DCL command string may be specified.

binmode FILEHANDLE

The "binmode" operator will attempt to insure that no translation of carriage control occurs on input from or output to this filehandle. Since this involves reopening the file and then restoring its file position indicator, if this function returns FALSE, the underlying filehandle may no longer point to an open file, or may point to a different position in the file than before "binmode" was called.

Note that "binmode" is generally not necessary when using normal filehandles; it is provided so that you can control I/O to existing record-structured files when necessary. You can also use the "vmsfopen" function in the VMS::Stdio extension to gain finer control of I/O to files and devices with different record structures.

crypt PLAINTEXT, USER

The "crypt" operator uses the "sys$hash_password" system service to generate the hashed representation of PLAINTEXT. If USER is a valid username, the algorithm and salt values are taken from that user's UAF record. If it is not, then the preferred algorithm and a salt of 0 are used. The quadword encrypted value is returned as an 8-character string.

The value returned by "crypt" may be compared against the encrypted password from the UAF returned by the "getpw*" functions, in order to authenticate users. If you're going to do this, remember that the encrypted password in the UAF was generated using uppercase username and password strings; you'll have to upcase the arguments to "crypt" to insure that you'll get the proper value:

    sub validate_passwd {
        my($user,$passwd) = @_;
        my($pwdhash);
        if ( !($pwdhash = (getpwnam($user))[1]) ||
               $pwdhash ne crypt("\U$passwd","\U$name") ) {
            intruder_alert($name);
        }
        return 1;
    }
    

die

"die" will force the native VMS exit status to be an SS$_ABORT code if neither of the $! or $? status values are ones that would cause the native status to be interpreted as being what VMS classifies as SEVERE_ERROR severity for DCL error handling.

When "PERL_VMS_POSIX_EXIT" is active (see "$?" below), the native VMS exit status value will have either one of the $! or $? or $^E or the Unix value 255 encoded into it in a way that the effective original value can be decoded by other programs written in C, including Perl and the GNV package. As per the normal non-VMS behavior of "die" if either $! or $? are non-zero, one of those values will be encoded into a native VMS status value. If both of the Unix status values are 0, and the $^E value is set one of ERROR or SEVERE_ERROR severity, then the $^E value will be used as the exit code as is. If none of the above apply, the Unix value of 255 will be encoded into a native VMS exit status value.

Please note a significant difference in the behavior of "die" in the "PERL_VMS_POSIX_EXIT" mode is that it does not force a VMS SEVERE_ERROR status on exit. The Unix exit values of 2 through 255 will be encoded in VMS status values with severity levels of SUCCESS. The Unix exit value of 1 will be encoded in a VMS status value with a severity level of ERROR. This is to be compatible with how the VMS C library encodes these values.

The minimum severity level set by "die" in "PERL_VMS_POSIX_EXIT" mode may be changed to be ERROR or higher in the future depending on the results of testing and further review.

See "$?" for a description of the encoding of the Unix value to produce a native VMS status containing it.

dump

Rather than causing Perl to abort and dump core, the "dump" operator invokes the VMS debugger. If you continue to execute the Perl program under the debugger, control will be transferred to the label specified as the argument to "dump", or, if no label was specified, back to the beginning of the program. All other state of the program (e.g. values of variables, open file handles) are not affected by calling "dump".

exec LIST

A call to "exec" will cause Perl to exit, and to invoke the command given as an argument to "exec" via "lib$do_command". If the argument begins with '@' or '$' (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 .Exe and the process defaults to expand the filespec) and pass the rest of "exec"'s argument to it as parameters. If the token has no file type, and matches a file with null type, then an attempt is made to determine whether the file is an executable image which should be invoked using "MCR" or a text file which should be passed to DCL as a command procedure.

fork

While in principle the "fork" operator could be implemented via (and with the same rather severe limitations as) the CRTL vfork() routine, and while some internal support to do just that is in place, the implementation has never been completed, making "fork" currently unavailable. A true kernel fork() is expected in a future version of VMS, and the pseudo-fork based on interpreter threads may be available in a future version of Perl on VMS (see perlfork). In the meantime, use "system", backticks, or piped filehandles to create subprocesses.

getpwent

getpwnam

getpwuid

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

gmtime

The "gmtime" operator will function properly if you have a working CRTL gmtime() routine, or if the logical name SYS$TIMEZONE_DIFFERENTIAL is defined as the number of seconds which must be added to UTC to yield local time. (This logical name is defined automatically if you are running a version of VMS with built-in UTC support.) If neither of these cases is true, a warning message is printed, and "undef" is returned.

kill

In most cases, "kill" is implemented via the undocumented system service $SIGPRC, which has the same calling sequence as $FORCEX, but throws an exception in the target process rather than forcing it to call $EXIT. Generally speaking, "kill" follows the behavior of the CRTL's kill() function, but unlike that function can be called from within a signal handler. Also, unlike the "kill" in some versions of the CRTL, Perl's "kill" checks the validity of the signal passed in and returns an error rather than attempting to send an unrecognized signal.

Also, negative signal values don't do anything special under VMS; they're just converted to the corresponding positive value.

qx//

See the entry on "backticks" above.

select (system call)

If Perl was not built with socket support, the system call version of "select" is not available at all. If socket support is present, then the system call version of "select" functions only for file descriptors attached to sockets. It will not provide information about regular files or pipes, since the CRTL select() routine does not provide this functionality.

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 "st_dev" and "st_ino" fields of a "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.

system LIST

The "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 the string begins with '@', it is treated as a DCL command unconditionally. Otherwise, if the first token contains a character used as a delimiter in file specification (e.g. ":" or "]"), an attempt is made to expand it using a default type of .Exe and the process defaults, and if successful, the resulting file is invoked via "MCR". This allows you to invoke an image directly simply by passing the file specification to "system", a common Unixish idiom. If the token has no file type, and matches a file with null type, then an attempt is made to determine whether the file is an executable image which should be invoked using "MCR" or a text file which should be passed to DCL as a command procedure.

If LIST consists of the empty string, "system" spawns an interactive DCL subprocess, in the same fashion as typing SPAWN at the DCL prompt.

Perl waits for the subprocess to complete before continuing execution in the current process. As described in perlfunc, the return value of "system" is a fake "status" which follows POSIX semantics unless the pragma "use vmsish 'status'" is in effect; see the description of $? in this document for more detail.

time

The value returned by "time" is the offset in seconds from 01-JAN-1970 00:00:00 (just like the CRTL's times() routine), in order to make life easier for code coming in from the POSIX/Unix world.

times

The array returned by the "times" operator is divided up according to the same rules the CRTL 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 a subprocess may or may not appear separately in the "child time" field, depending on whether times() keeps track of subprocesses separately. Note especially that the VAXCRTL (at least) keeps track only of subprocesses spawned using fork() and exec(); it will not accumulate the times of subprocesses spawned via pipes, system(), or backticks.

unlink LIST

"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 "unlink", no files with the names passed to "unlink" will exist. (Note: This can be changed at compile time; if you "use Config" and $Config{'d_unlink_all_versions'} is "define", then "unlink" will delete all versions of a file on the first call.)

"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 "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;
    }
    

(or you could just use "VMS::Stdio::remove", if you've installed the VMS::Stdio extension distributed with Perl). If "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.

This behavior of "unlink" is to be compatible with POSIX behavior and not traditional VMS behavior.

utime LIST

This operator changes only the modification time of the file (VMS revision date) on ODS-2 volumes and ODS-5 volumes without access dates enabled. On ODS-5 volumes with access dates enabled, the true access time is modified.

waitpid PID,FLAGS

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

Returns PID on success, -1 on error. The FLAGS argument is ignored in all cases.

Perl variables¶

The following VMS-specific information applies to the indicated "special" Perl variables, in addition to the general information in perlvar. Where there is a conflict, this information takes precedence.

%ENV

The operation of the %ENV array depends on the translation of the logical name PERL_ENV_TABLES. If defined, it should be a search list, each element of which specifies a location for %ENV elements. If you tell Perl to read or set the element "$ENV{"name"}", then Perl uses the translations of PERL_ENV_TABLES as follows:

   $  Define STORY  once,upon,a,time,there,was
   $  perl -e "for ($i = 0; $i <= 6; $i++) " -
   _$ -e "{ print $ENV{'story;'.$i},' '}"

    foreach my $key (qw[C-local keys you want promoted]) {
        my $temp = $ENV{$key}; # read from C-local array
        $ENV{$key} = $temp;    # and define as logical name
    }

    DELETE/LOGICAL *

$!

The string value of $! is that returned by the CRTL's strerror() function, so it will include the VMS message for VMS-specific errors. The numeric value of $! is the value of "errno", except if errno is EVMSERR, in which case $! contains the value of vaxc$errno. Setting $! always sets errno to the value specified. If this value is EVMSERR, it also sets vaxc$errno to 4 (NONAME-F-NOMSG), so that the string value of $! won't reflect the VMS error message from before $! was set.

$^E

This variable provides direct access to VMS status values in vaxc$errno, which are often more specific than the generic Unix-style error messages in $!. Its numeric value is the value of vaxc$errno, and its string value is the corresponding VMS message string, as retrieved by sys$getmsg(). Setting $^E sets vaxc$errno to the value specified.

While Perl attempts to keep the vaxc$errno value to be current, if errno is not EVMSERR, it may not be from the current operation.

$?

The "status value" returned in $? is synthesized from the actual exit status of the subprocess in a way that approximates POSIX wait(5) semantics, in order to allow Perl programs to portably test for successful completion of subprocesses. The low order 8 bits of $? are always 0 under VMS, since the termination status of a process may or may not have been generated by an exception.

The next 8 bits contain the termination status of the program.

If the child process follows the convention of C programs compiled with the _POSIX_EXIT macro set, the status value will contain the actual value of 0 to 255 returned by that program on a normal exit.

With the _POSIX_EXIT macro set, the Unix exit value of zero is represented as a VMS native status of 1, and the Unix values from 2 to 255 are encoded by the equation:

   VMS_status = 0x35a000 + (unix_value * 8) + 1.
    

And in the special case of Unix value 1 the encoding is:

   VMS_status = 0x35a000 + 8 + 2 + 0x10000000.
    

For other termination statuses, the severity portion of the subprocess's exit status is used: if the severity was success or informational, these bits are all 0; if the severity was warning, they contain a value of 1; if the severity was error or fatal error, they contain the actual severity bits, which turns out to be a value of 2 for error and 4 for severe_error. Fatal is another term for the severe_error status.

As a result, $? will always be zero if the subprocess's exit status indicated successful completion, and non-zero if a warning or error occurred or a program compliant with encoding _POSIX_EXIT values was run and set a status.

How can you tell the difference between a non-zero status that is the result of a VMS native error status or an encoded Unix status? You can not unless you look at the ${^CHILD_ERROR_NATIVE} value. The ${^CHILD_ERROR_NATIVE} value returns the actual VMS status value and check the severity bits. If the severity bits are equal to 1, then if the numeric value for $? is between 2 and 255 or 0, then $? accurately reflects a value passed back from a Unix application. If $? is 1, and the severity bits indicate a VMS error (2), then $? is from a Unix application exit value.

In practice, Perl scripts that call programs that return _POSIX_EXIT type status values will be expecting those values, and programs that call traditional VMS programs will either be expecting the previous behavior or just checking for a non-zero status.

And success is always the value 0 in all behaviors.

When the actual VMS termination status of the child is an error, internally the $! value will be set to the closest Unix errno value to that error so that Perl scripts that test for error messages will see the expected Unix style error message instead of a VMS message.

Conversely, when setting $? in an END block, an attempt is made to convert the POSIX value into a native status intelligible to the operating system upon exiting Perl. What this boils down to is that setting $? to zero results in the generic success value SS$_NORMAL, and setting $? to a non-zero value results in the generic failure status SS$_ABORT. See also "exit" in perlport.

With the "PERL_VMS_POSIX_EXIT" logical name defined as "ENABLE", setting $? will cause the new value to be encoded into $^E so that either the original parent or child exit status values
0 to 255 can be automatically recovered by C programs expecting _POSIX_EXIT behavior. If both a parent and a child exit value are non-zero, then it will be assumed that this is actually a VMS native status value to be passed through. The special value of 0xFFFF is almost a NOOP as it will cause the current native VMS status in the C library to become the current native Perl VMS status, and is handled this way as it is known to not be a valid native VMS status value. It is recommend that only values in the range of normal Unix parent or child status numbers, 0 to 255 are used.

The pragma "use vmsish 'status'" makes $? reflect the actual VMS exit status instead of the default emulation of POSIX status described above. This pragma also disables the conversion of non-zero values to SS$_ABORT when setting $? in an END block (but zero will still be converted to SS$_NORMAL).

Do not use the pragma "use vmsish 'status'" with "PERL_VMS_POSIX_EXIT" enabled, as they are at times requesting conflicting actions and the consequence of ignoring this advice will be undefined to allow future improvements in the POSIX exit handling.

In general, with "PERL_VMS_POSIX_EXIT" enabled, more detailed information will be available in the exit status for DCL scripts or other native VMS tools, and will give the expected information for Posix programs. It has not been made the default in order to preserve backward compatibility.

N.B. Setting "DECC$FILENAME_UNIX_REPORT" implicitly enables "PERL_VMS_POSIX_EXIT".

$|

Setting $| for an I/O stream causes data to be flushed all the way to disk on each write (i.e. not just to the underlying RMS buffers for a file). In other words, it's equivalent to calling fflush() and fsync() from C.

Standard modules with VMS-specific differences¶

Revision date¶

Please see the git repository for revision history.

AUTHOR¶

Charles Bailey bailey@cor.newman.upenn.edu Craig Berry craigberry@mac.com Dan Sugalski dan@sidhe.org John Malmberg wb8tyw@qsl.net