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



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 vmsperlATperl.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 installation 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 extensions.  It is used to
       generate several files needed to build the complete Perl and various extensions.  Once you've finished
       installing Perl, you can delete this image.

       Most of the complete Perl resides in the shareable image PerlShr.Exe, which provides a core to which the Perl
       executable image and all Perl extensions are linked.  You should place this image in Sys$Share, or define the
       logical name PerlShr to translate to the full file specification of this image.  It should be world readable.
       (Remember that if a user has execute only access to PerlShr, VMS will treat it as if it were a privileged
       shareable image, and will therefore require all downstream shareable images to be INSTALLed, etc.)

       Finally, Perl.Exe is an executable image containing the main entry point for Perl, as well as some initializa-
       tion 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 exten-
       sion.

       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 pro-
       vided: 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 exten-
       sion'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

       N.B. The procedure by which extensions are built and tested creates several levels (at least 4) under the
       directory in which the extension's source files live.  For this reason if you are running a version of VMS
       prior to V7.1 you shouldn't nest the source directory too deeply in your directory structure lest you exceed
       RMS' maximum of 8 levels of subdirectory in a filespec.  (You can use rooted logical names to get another 8
       levels of nesting, if you can't place the files near the top of the physical directory structure.)

       VMS support for this process in the current release of Perl is sufficient to handle most extensions.  However,
       it does not yet recognize extra libraries required to build shareable images which are part of an extension, so
       these must be added to the linker options file for the extension by hand.  For instance, if the PGPLOT exten-
       sion to Perl requires the PGPLOTSHR.EXE shareable image in order to properly link the Perl extension, then the
       line "PGPLOTSHR/Share" must be added to the linker options file PGPLOT.Opt produced during the build process
       for the Perl extension.

       By default, the shareable image for an extension is placed in the [.lib.site_perl.autoArch.Extname] directory
       of the installed Perl directory tree (where Arch is VMS_VAX or VMS_AXP, and Extname is the name of the exten-
       sion, with each "::" translated to ".").  (See the MakeMaker documentation for more details on installation
       options for extensions.)  However, it can be manually placed in any of several locations:

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

       ?   one of the directories in @INC, or

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

       ?   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.

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

       We've tried to minimize the dependence of Perl library modules on Unix syntax, but you may find that some of
       these, as well as some scripts written for Unix systems, will require that you use Unix syntax, since they will
       assume that '/' is the directory separator, etc.  If you find instances of this in the Perl distribution
       itself, please let us know, so we can try to work around them.

       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 glob-
       bing for a Unix shell, one can escape command line wildcards with double quotation marks """ around a perl pro-
       gram 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 per-
       formed. (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 expan-
       sion 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 asyn-
       chronous 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 expres-
       sion.  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 512.  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 double the MBX size from the default within a Perl
       program, use "$ENV{'PERL_MBX_SIZE'} = 1024;" and then open and use pipe constructs.  An alternative would be to
       issue the command:

           $ Define PERL_MBX_SIZE 1024

       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.

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 syn-
       tax:

       ?   "<file" reads stdin from "file",

       ?   ">file" writes stdout to "file",

       ?   ">>file" appends stdout to "file",

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

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

       ?   "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 sub-
       process.

       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.

       -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 trans-
           lates 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, endpwent, eof, eval, exec*,
           exists, exit, exp, fileno, getc, getlogin, getppid,
           getpwent*, getpwnam*, getpwuid*, glob, gmtime*, 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),
           select (system call)*, setpwent, shift, sin, sleep,
           sort, splice, split, sprintf, sqrt, srand, stat,
           study, substr, sysread, system*, syswrite, tell,
           telldir, tie, time, times*, tr///, uc, ucfirst, umask,
           undef, unlink*, unpack, untie, unshift, use, utime*,
           values, vec, wait, waitpid*, wantarray, warn, write, y///

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

           chroot, dbmclose, dbmopen, flock, fork*,
           getpgrp, getpriority, getgrent, getgrgid,
           getgrnam, setgrent, endgrent, ioctl, link, lstat,
           msgctl, msgget, msgsend, msgrcv, readlink, semctl,
           semget, semop, setpgrp, setpriority, shmctl, shmget,
           shmread, shmwrite, socketpair, symlink, 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

       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.

           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" func-
           tion 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;
               }

       dump
           Rather than causing Perl to abort and dump core, the "dump" operator invokes the VMS debugger.  If you con-
           tinue 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 file-
           spec) 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 limita-
           tions 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 filehan-
           dles 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 con-
           tains 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 logi-
           cal 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 CRTL's "kill()" function, so it will behave according to that
           function's documentation.  If you send a SIGKILL, however, the $DELPRC system service is called directly.
           This insures that the target process is actually deleted, if at all possible.  (The CRTL's "kill()" func-
           tion is presently implemented via $FORCEX, which is ignored by supervisor-mode images like DCL.)

           Also, negative signal values don't do anything special under VMS; they're just converted to the correspond-
           ing 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 rep-
           resent 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.

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

       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 CGI processing by some HTTP servers, then 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 ta-
               ble; 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.

           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.

           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 ker-
           nel 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 00) character, since a logi-
           cal 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.)  An element of the CRTL "environ" array can be set
           only if your copy of Perl knows about the CRTL's "setenv()" function.  (This is present only in some ver-
           sions of the DECCRTL; check $Config{d_setenv} to see whether your copy of Perl was built with a CRTL that
           has this function.)

           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; this
           can only be done if your copy of Perl knows about the CRTL "setenv()" function.)  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 expres-
           sion.)

           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 logicals 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 log-
           ical 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 logicals representing process-permanent files, such as "SYS$INPUT" and
           "SYS$OUTPUT".  The translations for these logicals 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 logicals, 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 mes-
           sage 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.

       $?  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 sta-
           tus of a process may or may not have been generated by an exception.  The next 8 bits are derived from the
           severity portion of the subprocess' exit status: 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 fatal
           error.

           As a result, $? will always be zero if the subprocess' exit status indicated successful completion, and
           non-zero if a warning or error occurred.  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 perl-
           port.

           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).

       $|  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
       This document was last updated on 01-May-2002, for Perl 5, patchlevel 8.

AUTHOR
       Charles Bailey  baileyATcor.edu Craig Berry  craigberryATmac.com Dan Sugalski  danATsidhe.org



perl v5.8.8                       2006-01-07                        PERLVMS(1)