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PERLVMS(1pm)           Perl Programmers Reference Guide           PERLVMS(1pm)




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

   Core Images
       During the build process, three Perl images are produced.  Miniperl.Exe
       is an executable image which contains all of the basic functionality of
       Perl, but cannot take advantage of Perl XS extensions and has a hard-
       wired list of library locations for loading pure-Perl modules.  It is
       used extensively to build and test Perl and various extensions, but is
       not installed.

       Most of the complete Perl resides in the shareable image PerlShr.Exe,
       which provides a core to which the Perl executable image and all Perl
       extensions are linked. It is generally located via the logical name
       PERLSHR.  While it's possible to put the image in SYS$SHARE to make it
       loadable, that's not recommended. And while you may wish to INSTALL the
       image for performance reasons, you should not install it with
       privileges; if you do, the result will not be what you expect as image
       privileges are disabled during Perl start-up.

       Finally, 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.

   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 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 "use" or
       "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 static
       configuration, the object code for the extension is linked directly
       into PerlShr.Exe, and is initialized whenever Perl is invoked.  In the
       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 "use"d or "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: Extshortname.xs (where
       Extshortname is the portion of the extension's name following the last
       "::"), containing the XS code, Extshortname.pm, the Perl library module
       for the extension, and Makefile.PL, a Perl script which uses the
       "MakeMaker" library modules supplied with Perl to generate a
       Descrip.MMS file for the extension.

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

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

   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
       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 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

       VMS support for this process in the current release of Perl is
       sufficient to handle most extensions.  (See the MakeMaker documentation
       for more details on installation options for extensions.)

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

       o   one of the directories in @INC, or

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

       o   Sys$Share or Sys$Library.

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


File specifications

   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 (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
       "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, 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 "./.../" in a Unix path is now translated to "[.^.^.^.]" instead of
       the traditional VMS "[...]".  To be compatible with what MakeMaker
       expects, if a VMS path cannot be translated to a Unix path, it is
       passed through unchanged, so "unixify("[...]")" will return "[...]".

       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.

   Filename Case
       Perl enables DECC$EFS_CASE_PRESERVE and DECC$ARGV_PARSE_STYLE by
       default.  Note that the latter only takes effect when extended parse is
       set in the process in which Perl is running.  When these features are
       explicitly disabled in the environment 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.

       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 expectations 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 "SET PROCESS
       /CASE_LOOKUP=SENSITIVE"). Perl does not currently support case
       sensitivity on VMS, but it may in the future, so Perl programs should
       use the "File::Spec->case_tolerant" method to determine the state, and
       not the $^O variable.

   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 "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.

   Wildcard expansion
       File specifications containing wildcards are allowed both on the
       command line and within Perl globs (e.g. "<*.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.  Similar to the behavior of wildcard globbing for a
       Unix shell, one can escape command line wildcards with double quotation
       marks """ around a perl program command line argument.  However, owing
       to the stripping of """ 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 PERL.C, PERL.EXE, PERL.H, and PERL.OBJ):

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

       in the following triple quoted manner:

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

       In both the case of unquoted command line arguments or in calls to
       "glob()" VMS wildcard expansion is performed. (csh-style wildcard
       expansion is available if you use "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 "[.t]*.*"
       will yield filespecs  like "perl_root:[t]base.dir", while the expansion
       of "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.

   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 "system"
       operator (see below).  In this case, Perl will wait for the subprocess
       to complete before continuing.

       The mailbox (MBX) that perl can create to communicate with a pipe
       defaults to a buffer size of 8192 on 64-bit systems, 512 on VAX.  The
       default buffer size is adjustable via the logical name PERL_MBX_SIZE
       provided that the value falls between 128 and the SYSGEN parameter
       MAXBUF inclusive.  For example, to set the mailbox size to 32767 use
       "$ENV{'PERL_MBX_SIZE'} = 32767;" and then open and use pipe constructs.
       An alternative would be to issue the command:

           $ Define PERL_MBX_SIZE 32767

       before running your wide record pipe program.  A larger value may
       improve performance at the expense of the BYTLM UAF quota.


PERL5LIB and PERLLIB

       The PERL5LIB and PERLLIB logical names work as documented in perl,
       except that the element separator is '|' instead of ':'.  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

   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:

       o   "<file" reads stdin from "file",

       o   ">file" writes stdout to "file",

       o   ">>file" appends stdout to "file",

       o   "2>file" writes stderr to "file",

       o   "2>>file" appends stderr to "file", and

       o   "2>&1" redirects stderr to stdout.

       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.

   Command line switches
       The following command line switches behave differently under VMS than
       described in 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.

       On newer 64 bit versions of OpenVMS, a process setting now controls if
       the quoting is needed to preserve the case of command line arguments.

       -i  If the "-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.)

       -S  If the "-S" or "-"S"" switch is present 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 .pl, and a type of
           .com, in that order.

       -u  The "-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.


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:

           CRTL_ENV
               This string tells Perl to consult the CRTL's internal "environ"
               array of key-value pairs, using name as the key.  In most
               cases, this contains only a few keys, but if Perl was invoked
               via the C "exec[lv]e()" function, as is the case for some
               embedded Perl applications or when running under a shell such
               as GNV bash, the "environ" array may have been populated by the
               calling program.

           CLISYM_[LOCAL]
               A string beginning with "CLISYM_"tells Perl to consult the
               CLI's symbol tables, using name as the name of the symbol.
               When reading an element of %ENV, the local symbol table is
               scanned first, followed by the global symbol table..  The
               characters following "CLISYM_" are significant when an element
               of %ENV is set or deleted: if the complete string is
               "CLISYM_LOCAL", the change is made in the local symbol table;
               otherwise the global symbol table is changed.

           Any other string
               If an element of PERL_ENV_TABLES translates to any other
               string, that string is used as the name of a logical name
               table, which is consulted using name as the logical name.  The
               normal search order of access modes is used.

           PERL_ENV_TABLES is translated once when Perl starts up; any changes
           you make while Perl is running do not affect the behavior of %ENV.
           If PERL_ENV_TABLES is not defined, then Perl defaults to consulting
           first the logical name tables specified by LNM$FILE_DEV, and then
           the CRTL "environ" array.  This default order is reversed when the
           logical name GNV$UNIX_SHELL is defined, such as when running under
           GNV bash.

           For operations on %ENV entries based on logical names or DCL
           symbols, the key string is treated as if it were entirely
           uppercase, regardless of the case actually specified in the Perl
           expression. Entries in %ENV based on the CRTL's environ array
           preserve the case of the key string when stored, and lookups are
           case sensitive.

           When an element of %ENV is read, the locations to which
           PERL_ENV_TABLES points are checked in order, and the value obtained
           from the first successful lookup is returned.  If the name of the
           %ENV element contains a semi-colon, it and any characters after it
           are removed.  These are ignored when the CRTL "environ" array or a
           CLI symbol table is consulted.  However, the name is looked up in a
           logical name table, the suffix after the semi-colon is treated as
           the translation index to be used for the lookup.   This lets you
           look up successive values for search list logical names.  For
           instance, if you say

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

           Perl will print "ONCE UPON A TIME THERE WAS", assuming, of course,
           that PERL_ENV_TABLES is set up so that the logical name "story" is
           found, rather than a CLI symbol or CRTL "environ" element with the
           same name.

           When an element of %ENV is set to a defined string, the
           corresponding definition is made in the location to which the first
           translation of PERL_ENV_TABLES points.  If this causes a logical
           name to be created, it is defined in supervisor mode.  (The same is
           done if an existing logical name was defined in executive or kernel
           mode; an existing user or supervisor mode logical name is reset to
           the new value.)  If the value is an empty string, the logical
           name's translation is defined as a single "NUL" (ASCII "\0")
           character, since a logical name cannot translate to a zero-length
           string.  (This restriction does not apply to CLI symbols or CRTL
           "environ" values; they are set to the empty string.)

           When an element of %ENV is set to "undef", the element is looked up
           as if it were being read, and if it is found, it is deleted.  (An
           item "deleted" from the CRTL "environ" array is set to the empty
           string.)  Using "delete" to remove an element from %ENV has a
           similar effect, but after the element is deleted, another attempt
           is made to look up the element, so an inner-mode logical name or a
           name in another location will replace the logical name just
           deleted. In either case, only the first value found searching
           PERL_ENV_TABLES is altered.  It is not possible at present to
           define a search list logical name via %ENV.

           The element $ENV{DEFAULT} is special: when read, it returns Perl's
           current default device and directory, and when set, it resets them,
           regardless of the definition of PERL_ENV_TABLES.  It cannot be
           cleared or deleted; attempts to do so are silently ignored.

           Note that if you want to pass on any elements of the C-local
           environ array to a subprocess which isn't started by fork/exec, or
           isn't running a C program, you can "promote" them to logical names
           in the current process, which will then be inherited by all
           subprocesses, by saying

               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
               }

           (You can't just say $ENV{$key} = $ENV{$key}, since the Perl
           optimizer is smart enough to elide the expression.)

           Don't try to clear %ENV by saying "%ENV = ();", it will throw a
           fatal error.  This is equivalent to doing the following from DCL:

               DELETE/LOGICAL *

           You can imagine how bad things would be if, for example, the
           SYS$MANAGER or SYS$SYSTEM logical names were deleted.

           At present, the first time you iterate over %ENV using "keys", or
           "values",  you will incur a time penalty as all logical names are
           read, in order to fully populate %ENV.  Subsequent iterations will
           not reread logical names, so they won't be as slow, but they also
           won't reflect any changes to logical name tables caused by other
           programs.

           You do need to be careful with the logical names representing
           process-permanent files, such as "SYS$INPUT" and "SYS$OUTPUT".  The
           translations for these logical names are prepended with a two-byte
           binary value (0x1B 0x00) that needs to be stripped off if you want
           to use it. (In previous versions of Perl it wasn't possible to get
           the values of these logical names, as the null byte acted as an
           end-of-string marker)

       $!  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

   SDBM_File
       SDBM_File works properly on VMS. It has, however, one minor difference.
       The database directory file created has a .sdbm_dir extension rather
       than a .dir extension. .dir files are VMS filesystem directory files,
       and using them for other purposes could cause unacceptable problems.


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



perl v5.24.0                      2016-03-01                      PERLVMS(1pm)

perl 5.24 - Generated Mon Dec 5 16:42:57 CST 2016
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