perlvms.pod

来自「MSYS在windows下模拟了一个类unix的终端」· POD 代码 · 共 886 行 · 第 1/3 页

=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, endpwent, eof, eval, exec*,
    exists, exit, exp, fileno, fork*, getc, getlogin,
    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, fcntl, flock,
    getpgrp, getppid, 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 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

=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.

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 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

The C<exec> operator behaves in one of two different ways.  
If called after a call to C<fork>, it will invoke the CRTL 
C<execv()> routine, passing its arguments to the subprocess 
created by C<fork> for execution.  In this case, it is 
subject to all limitations that affect C<execv()>.  (In 
particular, this usually means that the command executed in 
the subprocess must be an image compiled from C source code, 
and that your options for passing file descriptors and signal 
handlers to the subprocess are limited.)

If the call to C<exec> does not follow a call to C<fork>, it 
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.

You can use C<exec> in both ways within the same script, as 
long as you call C<fork> and C<exec> in pairs.  Perl
keeps track of how many times C<fork> and C<exec> have been
called, and will call the CRTL C<execv()> routine if there have
previously been more calls to C<fork> than to C<exec>.

=item fork

The C<fork> operator works in the same way as the CRTL 
C<vfork()> routine, which is quite different under VMS than 
under Unix.  Specifically, while C<fork> returns 0 after it 
is called and the subprocess PID after C<exec> is called, in 
both cases the thread of execution is within the parent 
process, so there is no opportunity to perform operations in 
the subprocess before calling C<exec>.

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

=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 CRTL's C<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 C<kill()>
function 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 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; see the description of C<$?> in this document
for more detail.  The actual VMS exit status of the subprocess
is available in C<$^S> (as long as you haven't used another Perl
function that resets C<$?> and C<$^S> in the meantime).

=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.