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+=head1 NAME
+
+perlvms - VMS-specific documentation for Perl
+
+=head1 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 F<[.pod]>
+subdirectory of the Perl distribution.
+
+We hope these notes will save you from confusion and lost
+sleep when writing Perl scripts on VMS. If you find we've
+missed something you think should appear here, please don't
+hesitate to drop a line to vmsperl@perl.org.
+
+=head1 Installation
+
+Directions for building and installing Perl 5 can be found in
+the file F<README.vms> in the main source directory of the
+Perl distribution..
+
+=head1 Organization of Perl Images
+
+=head2 Core Images
+
+During the installation process, three Perl images are produced.
+F<Miniperl.Exe> is an executable image which contains all of
+the basic functionality of Perl, but cannot take advantage of
+Perl extensions. It is used to generate several files needed
+to build the complete Perl and various extensions. Once you've
+finished installing Perl, you can delete this image.
+
+Most of the complete Perl resides in the shareable image
+F<PerlShr.Exe>, which provides a core to which the Perl executable
+image and all Perl extensions are linked. You should place this
+image in F<Sys$Share>, or define the logical name F<PerlShr> to
+translate to the full file specification of this image. It should
+be world readable. (Remember that if a user has execute only access
+to F<PerlShr>, VMS will treat it as if it were a privileged shareable
+image, and will therefore require all downstream shareable images to be
+INSTALLed, etc.)
+
+
+Finally, F<Perl.Exe> is an executable image containing the main
+entry point for Perl, as well as some initialization code. It
+should be placed in a public directory, and made world executable.
+In order to run Perl with command line arguments, you should
+define a foreign command to invoke this image.
+
+=head2 Perl Extensions
+
+Perl extensions are packages which provide both XS and Perl code
+to add new functionality to perl. (XS is a meta-language which
+simplifies writing C code which interacts with Perl, see
+L<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
+C<use> or C<require> statement, and usually defines a Perl
+package containing the extension.
+
+The portion of the extension provided by the XS code may be
+connected to the rest of Perl in either of two ways. In the
+B<static> configuration, the object code for the extension is
+linked directly into F<PerlShr.Exe>, and is initialized whenever
+Perl is invoked. In the B<dynamic> configuration, the extension's
+machine code is placed into a separate shareable image, which is
+mapped by Perl's DynaLoader when the extension is C<use>d or
+C<require>d in your script. This allows you to maintain the
+extension as a separate entity, at the cost of keeping track of the
+additional shareable image. Most extensions can be set up as either
+static or dynamic.
+
+The source code for an extension usually resides in its own
+directory. At least three files are generally provided:
+I<Extshortname>F<.xs> (where I<Extshortname> is the portion of
+the extension's name following the last C<::>), containing
+the XS code, I<Extshortname>F<.pm>, the Perl library module
+for the extension, and F<Makefile.PL>, a Perl script which uses
+the C<MakeMaker> library modules supplied with Perl to generate
+a F<Descrip.MMS> file for the extension.
+
+=head2 Installing static extensions
+
+Since static extensions are incorporated directly into
+F<PerlShr.Exe>, you'll have to rebuild Perl to incorporate a
+new extension. You should edit the main F<Descrip.MMS> or F<Makefile>
+you use to build Perl, adding the extension's name to the C<ext>
+macro, and the extension's object file to the C<extobj> macro.
+You'll also need to build the extension's object file, either
+by adding dependencies to the main F<Descrip.MMS>, or using a
+separate F<Descrip.MMS> for the extension. Then, rebuild
+F<PerlShr.Exe> to incorporate the new code.
+
+Finally, you'll need to copy the extension's Perl library
+module to the F<[.>I<Extname>F<]> subdirectory under one
+of the directories in C<@INC>, where I<Extname> is the name
+of the extension, with all C<::> replaced by C<.> (e.g.
+the library module for extension Foo::Bar would be copied
+to a F<[.Foo.Bar]> subdirectory).
+
+=head2 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 F<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 B<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
+
+I<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 F<PGPLOT> extension to Perl requires the
+F<PGPLOTSHR.EXE> shareable image in order to properly link
+the Perl extension, then the line C<PGPLOTSHR/Share> must
+be added to the linker options file F<PGPLOT.Opt> produced
+during the build process for the Perl extension.
+
+By default, the shareable image for an extension is placed in
+the F<[.lib.site_perl.auto>I<Arch>.I<Extname>F<]> directory of the
+installed Perl directory tree (where I<Arch> is F<VMS_VAX> or
+F<VMS_AXP>, and I<Extname> is the name of the extension, with
+each C<::> translated to C<.>). (See the MakeMaker documentation
+for more details on installation options for extensions.)
+However, it can be manually placed in any of several locations:
+
+=over 4
+
+=item *
+
+the F<[.Lib.Auto.>I<Arch>I<$PVers>I<Extname>F<]> subdirectory
+of one of the directories in C<@INC> (where I<PVers>
+is the version of Perl you're using, as supplied in C<$]>,
+with '.' converted to '_'), or
+
+=item *
+
+one of the directories in C<@INC>, or
+
+=item *
+
+a directory which the extensions Perl library module
+passes to the DynaLoader when asking it to map
+the shareable image, or
+
+=item *
+
+F<Sys$Share> or F<Sys$Library>.
+
+=back
+
+If the shareable image isn't in any of these places, you'll need
+to define a logical name I<Extshortname>, where I<Extshortname>
+is the portion of the extension's name after the last C<::>, which
+translates to the full file specification of the shareable image.
+
+=head1 File specifications
+
+=head2 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 (I<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
+C<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, I<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$FILENAME_UNIX_REPORT modifies traditional
+Perl behavior in the conversion of file specifications from Unix to VMS
+format in order to follow the extended character handling rules now
+expected by the CRTL. Specifically, when this feature is in effect, the
+C<./.../> in a Unix path is now translated to C<[.^.^.^.]> instead of
+the traditional VMS C<[...]>. To be compatible with what MakeMaker
+expects, if a VMS path cannot be translated to a Unix path, it is
+passed through unchanged, so C<unixify("[...]")> will return C<[...]>.
+
+The handling of extended characters is largely complete in the
+VMS-specific C infrastructure of Perl, but more work is still needed to
+fully support extended syntax filenames in several core modules. In
+particular, at this writing PathTools has only partial support for
+directories containing some extended characters.
+
+There are several ambiguous cases where a conversion routine cannot
+determine whether an input filename is in Unix format or in VMS format,
+since now both VMS and Unix file specifications may have characters in
+them that could be mistaken for syntax delimiters of the other type. So
+some pathnames simply cannot be used in a mode that allows either type
+of pathname to be present. Perl will tend to assume that an ambiguous
+filename is in Unix format.
+
+Allowing "." as a version delimiter is simply incompatible with
+determining whether a pathname is in VMS format or in Unix format with
+extended file syntax. There is no way to know whether "perl-5.8.6" is a
+Unix "perl-5.8.6" or a VMS "perl-5.8;6" when passing it to unixify() or
+vmsify().
+
+The DECC$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.
+
+=head2 Filename Case
+
+Perl follows VMS defaults and override settings in preserving (or not
+preserving) filename case. Case is not preserved on ODS-2 formatted
+volumes on any architecture. On ODS-5 volumes, filenames may be case
+preserved depending on process and feature settings. Perl now honors
+DECC$EFS_CASE_PRESERVE and DECC$ARGV_PARSE_STYLE on those systems where
+the CRTL supports these features. When these features are not enabled
+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.
+
+I<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 expections 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 C<SET PROCESS
+/CASE_LOOKUP=SENSITIVE>). Perl does not currently suppport case
+sensitivity on VMS, but it may in the future, so Perl programs should
+use the C<< File::Spec->case_tolerant >> method to determine the state, and
+not the C<$^O> variable.
+
+=head2 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 C<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.
+
+=head2 Wildcard expansion
+
+File specifications containing wildcards are allowed both on
+the command line and within Perl globs (e.g. C<E<lt>*.cE<gt>>). 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 C<"> around a perl program command line argument. However,
+owing to the stripping of C<"> 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 F<PERL.C>, F<PERL.EXE>,
+F<PERL.H>, and F<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 C<glob()> VMS wildcard expansion is performed. (csh-style
+wildcard expansion is available if you use C<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 C<[.t]*.*> will yield filespecs like
+"perl_root:[t]base.dir", while the expansion of C<t/*/*> will
+yield filespecs like "t/base.dir". (This is done to match
+the behavior of glob expansion performed by Unix shells.)
+
+Similarly, the resultant filespec will contain the file version
+only if one was present in the input filespec.
+
+
+=head2 Pipes
+
+Input and output pipes to Perl filehandles are supported; the
+"file name" is passed to lib$spawn() for asynchronous
+execution. You should be careful to close any pipes you have
+opened in a Perl script, lest you leave any "orphaned"
+subprocesses around when Perl exits.
+
+You may also use backticks to invoke a DCL subprocess, whose
+output is used as the return value of the expression. The
+string between the backticks is handled as if it were the
+argument to the C<system> operator (see below). In this case,
+Perl will wait for the subprocess to complete before continuing.
+
+The mailbox (MBX) that perl can create to communicate with a pipe
+defaults to a buffer size of 8192 on 64-bit systems, 512 on VAX. The
+default buffer size is adjustable via the logical name PERL_MBX_SIZE
+provided that the value falls between 128 and the SYSGEN parameter
+MAXBUF inclusive. For example, to set the mailbox size to 32767 use
+C<$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.
+
+=head1 PERL5LIB and PERLLIB
+
+The PERL5LIB and PERLLIB logical names work as documented in L<perl>,
+except that the element separator is '|' instead of ':'. The
+directory specifications may use either VMS or Unix syntax.
+
+=head1 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 C<TERM> to be C<xterm>,
+and the environment variable C<DISPLAY> to exist. C<xterm> must be in
+lower case.
+
+ $define TERM "xterm"
+
+ $define DISPLAY "hostname:0.0"
+
+Currently the value of C<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
+
+
+=head1 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 usally not practical.
+
+Starting Perl in the VMS debugger may change the program execution
+profile in a way that such problems are not reproduced.
+
+The C<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.
+
+=head1 Command line
+
+=head2 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:
+
+=over 4
+
+=item *
+
+C<E<lt>file> reads stdin from C<file>,
+
+=item *
+
+C<E<gt>file> writes stdout to C<file>,
+
+=item *
+
+C<E<gt>E<gt>file> appends stdout to C<file>,
+
+=item *
+
+C<2E<gt>file> writes stderr to C<file>,
+
+=item *
+
+C<2E<gt>E<gt>file> appends stderr to C<file>, and
+
+=item *
+
+C<< 2>&1 >> redirects stderr to stdout.
+
+=back
+
+In addition, output may be piped to a subprocess, using the
+character '|'. Anything after this character on the command
+line is passed to a subprocess for execution; the subprocess
+takes the output of Perl as its input.
+
+Finally, if the command line ends with '&', the entire
+command is run in the background as an asynchronous
+subprocess.
+
+=head2 Command line switches
+
+The following command line switches behave differently under
+VMS than described in L<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.
+
+=over 4
+
+=item -i
+
+If the C<-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.)
+
+=item -S
+
+If the C<"-S"> or C<-"S"> switch is present I<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 F<.pl>, and a type of F<.com>, in that order.
+
+=item -u
+
+The C<-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.
+
+=back
+
+=head1 Perl functions
+
+As of the time this document was last revised, the following
+Perl functions were implemented in the VMS port of Perl
+(functions marked with * are discussed in more detail below):
+
+ file tests*, abs, alarm, atan, 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
+
+=over 4
+
+=item File tests
+
+The tests C<-b>, C<-B>, C<-c>, C<-C>, C<-d>, C<-e>, C<-f>,
+C<-o>, C<-M>, C<-s>, C<-S>, C<-t>, C<-T>, and C<-z> work as
+advertised. The return values for C<-r>, C<-w>, and C<-x>
+tell you whether you can actually access the file; this may
+not reflect the UIC-based file protections. Since real and
+effective UIC don't differ under VMS, C<-O>, C<-R>, C<-W>,
+and C<-X> are equivalent to C<-o>, C<-r>, C<-w>, and C<-x>.
+Similarly, several other tests, including C<-A>, C<-g>, C<-k>,
+C<-l>, C<-p>, and C<-u>, aren't particularly meaningful under
+VMS, and the values returned by these tests reflect whatever
+your CRTL C<stat()> routine does to the equivalent bits in the
+st_mode field. Finally, C<-d> returns true if passed a device
+specification without an explicit directory (e.g. C<DUA1:>), as
+well as if passed a directory.
+
+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 (C<-r>, C<-w>, and C<-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 C<$!> indicating that the file does not exist. You can
+use C<stat> on these files, since that checks UIC-based protection
+only, and then manually check the appropriate bits, as defined by
+your C compiler's F<stat.h>, in the mode value it returns, if you
+need an approximation of the file's protections.
+
+=item backticks
+
+Backticks create a subprocess, and pass the enclosed string
+to it for execution as a DCL command. Since the subprocess is
+created directly via C<lib$spawn()>, any valid DCL command string
+may be specified.
+
+=item binmode FILEHANDLE
+
+The C<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 C<binmode>
+was called.
+
+Note that C<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
+C<vmsfopen> function in the VMS::Stdio extension to gain finer
+control of I/O to files and devices with different record structures.
+
+=item crypt PLAINTEXT, USER
+
+The C<crypt> operator uses the C<sys$hash_password> system
+service to generate the hashed representation of PLAINTEXT.
+If USER is a valid username, the algorithm and salt values
+are taken from that user's UAF record. If it is not, then
+the preferred algorithm and a salt of 0 are used. The
+quadword encrypted value is returned as an 8-character string.
+
+The value returned by C<crypt> may be compared against
+the encrypted password from the UAF returned by the C<getpw*>
+functions, in order to authenticate users. If you're
+going to do this, remember that the encrypted password in
+the UAF was generated using uppercase username and
+password strings; you'll have to upcase the arguments to
+C<crypt> to insure that you'll get the proper value:
+
+ sub validate_passwd {
+ my($user,$passwd) = @_;
+ my($pwdhash);
+ if ( !($pwdhash = (getpwnam($user))[1]) ||
+ $pwdhash ne crypt("\U$passwd","\U$name") ) {
+ intruder_alert($name);
+ }
+ return 1;
+ }
+
+
+=item die
+
+C<die> will force the native VMS exit status to be an SS$_ABORT code
+if neither of the $! or $? status values are ones that would cause
+the native status to be interpreted as being what VMS classifies as
+SEVERE_ERROR severity for DCL error handling.
+
+When C<PERL_VMS_POSIX_EXIT> is active (see L</"$?"> below), the native VMS exit
+status value will have either one of the C<$!> or C<$?> or C<$^E> or
+the Unix value 255 encoded into it in a way that the effective original
+value can be decoded by other programs written in C, including Perl
+and the GNV package. As per the normal non-VMS behavior of C<die> if
+either C<$!> or C<$?> are non-zero, one of those values will be
+encoded into a native VMS status value. If both of the Unix status
+values are 0, and the C<$^E> value is set one of ERROR or SEVERE_ERROR
+severity, then the C<$^E> value will be used as the exit code as is.
+If none of the above apply, the Unix value of 255 will be encoded into
+a native VMS exit status value.
+
+Please note a significant difference in the behavior of C<die> in
+the C<PERL_VMS_POSIX_EXIT> mode is that it does not force a VMS
+SEVERE_ERROR status on exit. The Unix exit values of 2 through
+255 will be encoded in VMS status values with severity levels of
+SUCCESS. The Unix exit value of 1 will be encoded in a VMS status
+value with a severity level of ERROR. This is to be compatible with
+how the VMS C library encodes these values.
+
+The minimum severity level set by C<die> in C<PERL_VMS_POSIX_EXIT> mode
+may be changed to be ERROR or higher in the future depending on the
+results of testing and further review.
+
+See L</"$?"> for a description of the encoding of the Unix value to
+produce a native VMS status containing it.
+
+
+=item dump
+
+Rather than causing Perl to abort and dump core, the C<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
+C<dump>, or, if no label was specified, back to the
+beginning of the program. All other state of the program
+(I<e.g.> values of variables, open file handles) are not
+affected by calling C<dump>.
+
+=item exec LIST
+
+A call to C<exec> will cause Perl to exit, and to invoke the command
+given as an argument to C<exec> via C<lib$do_command>. If the
+argument begins with '@' or '$' (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 F<.Exe> and the process
+defaults to expand the filespec) and pass the rest of C<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 C<MCR> or a text file which should be passed to DCL as a
+command procedure.
+
+=item fork
+
+While in principle the C<fork> operator could be implemented via
+(and with the same rather severe limitations as) the CRTL C<vfork()>
+routine, and while some internal support to do just that is in
+place, the implementation has never been completed, making C<fork>
+currently unavailable. A true kernel C<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
+L<perlfork>). In the meantime, use C<system>, backticks, or piped
+filehandles to create subprocesses.
+
+=item getpwent
+
+=item getpwnam
+
+=item getpwuid
+
+These operators obtain the information described in L<perlfunc>,
+if you have the privileges necessary to retrieve the named user's
+UAF information via C<sys$getuai>. If not, then only the C<$name>,
+C<$uid>, and C<$gid> items are returned. The C<$dir> item contains
+the login directory in VMS syntax, while the C<$comment> item
+contains the login directory in Unix syntax. The C<$gcos> item
+contains the owner field from the UAF record. The C<$quota>
+item is not used.
+
+=item gmtime
+
+The C<gmtime> operator will function properly if you have a
+working CRTL C<gmtime()> routine, or if the logical name
+SYS$TIMEZONE_DIFFERENTIAL is defined as the number of seconds
+which must be added to UTC to yield local time. (This logical
+name is defined automatically if you are running a version of
+VMS with built-in UTC support.) If neither of these cases is
+true, a warning message is printed, and C<undef> is returned.
+
+=item kill
+
+In most cases, C<kill> is implemented via the undocumented system
+service C<$SIGPRC>, which has the same calling sequence as C<$FORCEX>, but
+throws an exception in the target process rather than forcing it to call
+C<$EXIT>. Generally speaking, C<kill> follows the behavior of the
+CRTL's C<kill()> function, but unlike that function can be called from
+within a signal handler. Also, unlike the C<kill> in some versions of
+the CRTL, Perl's C<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.
+
+=item qx//
+
+See the entry on C<backticks> above.
+
+=item select (system call)
+
+If Perl was not built with socket support, the system call
+version of C<select> is not available at all. If socket
+support is present, then the system call version of
+C<select> functions only for file descriptors attached
+to sockets. It will not provide information about regular
+files or pipes, since the CRTL C<select()> routine does not
+provide this functionality.
+
+=item stat EXPR
+
+Since VMS keeps track of files according to a different scheme
+than Unix, it's not really possible to represent the file's ID
+in the C<st_dev> and C<st_ino> fields of a C<struct stat>. Perl
+tries its best, though, and the values it uses are pretty unlikely
+to be the same for two different files. We can't guarantee this,
+though, so caveat scriptor.
+
+=item system LIST
+
+The C<system> operator creates a subprocess, and passes its
+arguments to the subprocess for execution as a DCL command.
+Since the subprocess is created directly via C<lib$spawn()>, any
+valid DCL command string may be specified. If the string begins with
+'@', it is treated as a DCL command unconditionally. Otherwise, if
+the first token contains a character used as a delimiter in file
+specification (e.g. C<:> or C<]>), an attempt is made to expand it
+using a default type of F<.Exe> and the process defaults, and if
+successful, the resulting file is invoked via C<MCR>. This allows you
+to invoke an image directly simply by passing the file specification
+to C<system>, a common Unixish idiom. If the token has no file type,
+and matches a file with null type, then an attempt is made to
+determine whether the file is an executable image which should be
+invoked using C<MCR> or a text file which should be passed to DCL
+as a command procedure.
+
+If LIST consists of the empty string, C<system> spawns an
+interactive DCL subprocess, in the same fashion as typing
+B<SPAWN> at the DCL prompt.
+
+Perl waits for the subprocess to complete before continuing
+execution in the current process. As described in L<perlfunc>,
+the return value of C<system> is a fake "status" which follows
+POSIX semantics unless the pragma C<use vmsish 'status'> is in
+effect; see the description of C<$?> in this document for more
+detail.
+
+=item time
+
+The value returned by C<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.
+
+=item times
+
+The array returned by the C<times> operator is divided up
+according to the same rules the CRTL C<times()> routine.
+Therefore, the "system time" elements will always be 0, since
+there is no difference between "user time" and "system" time
+under VMS, and the time accumulated by a subprocess may or may
+not appear separately in the "child time" field, depending on
+whether L<times> keeps track of subprocesses separately. Note
+especially that the VAXCRTL (at least) keeps track only of
+subprocesses spawned using L<fork> and L<exec>; it will not
+accumulate the times of subprocesses spawned via pipes, L<system>,
+or backticks.
+
+=item unlink LIST
+
+C<unlink> will delete the highest version of a file only; in
+order to delete all versions, you need to say
+
+ 1 while unlink LIST;
+
+You may need to make this change to scripts written for a
+Unix system which expect that after a call to C<unlink>,
+no files with the names passed to C<unlink> will exist.
+(Note: This can be changed at compile time; if you
+C<use Config> and C<$Config{'d_unlink_all_versions'}> is
+C<define>, then C<unlink> will delete all versions of a
+file on the first call.)
+
+C<unlink> will delete a file if at all possible, even if it
+requires changing file protection (though it won't try to
+change the protection of the parent directory). You can tell
+whether you've got explicit delete access to a file by using the
+C<VMS::Filespec::candelete> operator. For instance, in order
+to delete only files to which you have delete access, you could
+say something like
+
+ sub safe_unlink {
+ my($file,$num);
+ foreach $file (@_) {
+ next unless VMS::Filespec::candelete($file);
+ $num += unlink $file;
+ }
+ $num;
+ }
+
+(or you could just use C<VMS::Stdio::remove>, if you've installed
+the VMS::Stdio extension distributed with Perl). If C<unlink> has to
+change the file protection to delete the file, and you interrupt it
+in midstream, the file may be left intact, but with a changed ACL
+allowing you delete access.
+
+This behavior of C<unlink> is to be compatible with POSIX behavior
+and not traditional VMS behavior.
+
+=item utime LIST
+
+This operator changes only the modification time of the file (VMS
+revision date) on ODS-2 volumes and ODS-5 volumes without access
+dates enabled. On ODS-5 volumes with access dates enabled, the
+true access time is modified.
+
+=item waitpid PID,FLAGS
+
+If PID is a subprocess started by a piped C<open()> (see L<open>),
+C<waitpid> will wait for that subprocess, and return its final status
+value in C<$?>. If PID is a subprocess created in some other way (e.g.
+SPAWNed before Perl was invoked), C<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 C<-w> switch, a warning will be issued.)
+
+Returns PID on success, -1 on error. The FLAGS argument is ignored
+in all cases.
+
+=back
+
+=head1 Perl variables
+
+The following VMS-specific information applies to the indicated
+"special" Perl variables, in addition to the general information
+in L<perlvar>. Where there is a conflict, this information
+takes precedence.
+
+=over 4
+
+=item %ENV
+
+The operation of the C<%ENV> array depends on the translation
+of the logical name F<PERL_ENV_TABLES>. If defined, it should
+be a search list, each element of which specifies a location
+for C<%ENV> elements. If you tell Perl to read or set the
+element C<$ENV{>I<name>C<}>, then Perl uses the translations of
+F<PERL_ENV_TABLES> as follows:
+
+=over 4
+
+=item CRTL_ENV
+
+This string tells Perl to consult the CRTL's internal C<environ>
+array of key-value pairs, using I<name> as the key. In most cases,
+this contains only a few keys, but if Perl was invoked via the C
+C<exec[lv]e()> function, as is the case for CGI processing by some
+HTTP servers, then the C<environ> array may have been populated by
+the calling program.
+
+=item CLISYM_[LOCAL]
+
+A string beginning with C<CLISYM_>tells Perl to consult the CLI's
+symbol tables, using I<name> as the name of the symbol. When reading
+an element of C<%ENV>, the local symbol table is scanned first, followed
+by the global symbol table.. The characters following C<CLISYM_> are
+significant when an element of C<%ENV> is set or deleted: if the
+complete string is C<CLISYM_LOCAL>, the change is made in the local
+symbol table; otherwise the global symbol table is changed.
+
+=item Any other string
+
+If an element of F<PERL_ENV_TABLES> translates to any other string,
+that string is used as the name of a logical name table, which is
+consulted using I<name> as the logical name. The normal search
+order of access modes is used.
+
+=back
+
+F<PERL_ENV_TABLES> is translated once when Perl starts up; any changes
+you make while Perl is running do not affect the behavior of C<%ENV>.
+If F<PERL_ENV_TABLES> is not defined, then Perl defaults to consulting
+first the logical name tables specified by F<LNM$FILE_DEV>, and then
+the CRTL C<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 C<%ENV> is read, the locations to which
+F<PERL_ENV_TABLES> points are checked in order, and the value
+obtained from the first successful lookup is returned. If the
+name of the C<%ENV> element contains a semi-colon, it and
+any characters after it are removed. These are ignored when
+the CRTL C<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 C<ONCE UPON A TIME THERE WAS>, assuming, of course,
+that F<PERL_ENV_TABLES> is set up so that the logical name C<story>
+is found, rather than a CLI symbol or CRTL C<environ> element with
+the same name.
+
+When an element of C<%ENV> is set to a defined string, the
+corresponding definition is made in the location to which the
+first translation of F<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 00) character, since a logical name cannot translate to a
+zero-length string. (This restriction does not apply to CLI symbols
+or CRTL C<environ> values; they are set to the empty string.)
+An element of the CRTL C<environ> array can be set only if your
+copy of Perl knows about the CRTL's C<setenv()> function. (This is
+present only in some versions of the DECCRTL; check C<$Config{d_setenv}>
+to see whether your copy of Perl was built with a CRTL that has this
+function.)
+
+When an element of C<%ENV> is set to C<undef>,
+the element is looked up as if it were being read, and if it is
+found, it is deleted. (An item "deleted" from the CRTL C<environ>
+array is set to the empty string; this can only be done if your
+copy of Perl knows about the CRTL C<setenv()> function.) Using
+C<delete> to remove an element from C<%ENV> has a similar effect,
+but after the element is deleted, another attempt is made to
+look up the element, so an inner-mode logical name or a name in
+another location will replace the logical name just deleted.
+In either case, only the first value found searching PERL_ENV_TABLES
+is altered. It is not possible at present to define a search list
+logical name via %ENV.
+
+The element C<$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 F<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} = $temp; # and define as logical name
+ }
+
+(You can't just say C<$ENV{$key} = $ENV{$key}>, since the
+Perl optimizer is smart enough to elide the expression.)
+
+Don't try to clear C<%ENV> by saying C<%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
+C<keys>, or C<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 C<SYS$INPUT> and C<SYS$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 wantto 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)
+
+=item $!
+
+The string value of C<$!> is that returned by the CRTL's
+strerror() function, so it will include the VMS message for
+VMS-specific errors. The numeric value of C<$!> is the
+value of C<errno>, except if errno is EVMSERR, in which
+case C<$!> contains the value of vaxc$errno. Setting C<$!>
+always sets errno to the value specified. If this value is
+EVMSERR, it also sets vaxc$errno to 4 (NONAME-F-NOMSG), so
+that the string value of C<$!> won't reflect the VMS error
+message from before C<$!> was set.
+
+=item $^E
+
+This variable provides direct access to VMS status values
+in vaxc$errno, which are often more specific than the
+generic Unix-style error messages in C<$!>. Its numeric value
+is the value of vaxc$errno, and its string value is the
+corresponding VMS message string, as retrieved by sys$getmsg().
+Setting C<$^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.
+
+=item $?
+
+The "status value" returned in C<$?> 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 C<$?> are always 0 under VMS, since the
+termination status of a process may or may not have been
+generated by an exception.
+
+The next 8 bits contain the termination status of the program.
+
+If the child process follows the convention of C programs
+compiled with the _POSIX_EXIT macro set, the status value will
+contain the actual value of 0 to 255 returned by that program
+on a normal exit.
+
+With the _POSIX_EXIT macro set, the Unix exit value of zero is
+represented as a VMS native status of 1, and the Unix values
+from 2 to 255 are encoded by the equation:
+
+ VMS_status = 0x35a000 + (unix_value * 8) + 1.
+
+And in the special case of Unix value 1 the encoding is:
+
+ VMS_status = 0x35a000 + 8 + 2 + 0x10000000.
+
+For other termination statuses, the severity portion of the
+subprocess's exit status is used: if the severity was success or
+informational, these bits are all 0; if the severity was
+warning, they contain a value of 1; if the severity was
+error or fatal error, they contain the actual severity bits,
+which turns out to be a value of 2 for error and 4 for severe_error.
+Fatal is another term for the severe_error status.
+
+As a result, C<$?> 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 ${^CHILD_ERROR_NATIVE} value returns the actual VMS status value
+and check the severity bits. If the severity bits are equal to 1,
+then if the numeric value for C<$?> is between 2 and 255 or 0, then
+C<$?> accurately reflects a value passed back from a Unix application.
+If C<$?> is 1, and the severity bits indicate a VMS error (2), then
+C<$?> is from a Unix application exit value.
+
+In practice, Perl scripts that call programs that return _POSIX_EXIT
+type status values will be expecting those values, and programs that
+call traditional VMS programs will either be expecting the previous
+behavior or just checking for a non-zero status.
+
+And success is always the value 0 in all behaviors.
+
+When the actual VMS termination status of the child is an error,
+internally the C<$!> 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 C<$?> in an END block, an attempt is made
+to convert the POSIX value into a native status intelligible to
+the operating system upon exiting Perl. What this boils down to
+is that setting C<$?> to zero results in the generic success value
+SS$_NORMAL, and setting C<$?> to a non-zero value results in the
+generic failure status SS$_ABORT. See also L<perlport/exit>.
+
+With the C<PERL_VMS_POSIX_EXIT> logical name defined as "ENABLE",
+setting C<$?> will cause the new value to be encoded into C<$^E>
+so that either the original parent or child exit status values
+ 0 to 255 can be automatically recovered by C programs expecting
+_POSIX_EXIT behavior. If both a parent and a child exit value are
+non-zero, then it will be assumed that this is actually a VMS native
+status value to be passed through. The special value of 0xFFFF is
+almost a NOOP as it will cause the current native VMS status in the
+C library to become the current native Perl VMS status, and is handled
+this way as it is known to not be a valid native VMS status value.
+It is recommend that only values in the range of normal Unix parent or
+child status numbers, 0 to 255 are used.
+
+The pragma C<use vmsish 'status'> makes C<$?> 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$_ABORT when setting C<$?> in an END
+block (but zero will still be converted to SS$_NORMAL).
+
+Do not use the pragma C<use vmsish 'status'> with C<PERL_VMS_POSIX_EXIT>
+enabled, as they are at times requesting conflicting actions and the
+consequence of ignoring this advice will be undefined to allow future
+improvements in the POSIX exit handling.
+
+In general, with C<PERL_VMS_POSIX_EXIT> enabled, more detailed information
+will be availble in the exit status for DCL scripts or other native VMS tools,
+and will give the expected information for Posix programs. It has not been
+made the default in order to preserve backward compatibility.
+
+N.B. Setting C<DECC$FILENAME_UNIX_REPORT> implicitly enables
+C<PERL_VMS_POSIX_EXIT>.
+
+=item $|
+
+Setting C<$|> for an I/O stream causes data to be flushed
+all the way to disk on each write (I<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.
+
+=back
+
+=head1 Standard modules with VMS-specific differences
+
+=head2 SDBM_File
+
+SDBM_File works properly on VMS. It has, however, one minor
+difference. The database directory file created has a F<.sdbm_dir>
+extension rather than a F<.dir> extension. F<.dir> files are VMS filesystem
+directory files, and using them for other purposes could cause unacceptable
+problems.
+
+=head1 Revision date
+
+Please see the git repository for revision history.
+
+=head1 AUTHOR
+
+Charles Bailey bailey@cor.newman.upenn.edu
+Craig Berry craigberry@mac.com
+Dan Sugalski dan@sidhe.org
+John Malmberg wb8tyw@qsl.net