perlvms.1

视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

status value will have either one of the \f(CW$!\fR or \f(CW$?\fR or \f(CW$^E\fR or
the \s-1UNIX\s0 value 255 encoded into it in a way that the effective original
value can be decoded by other programs written in C, including Perl
and the \s-1GNV\s0 package.  As per the normal non-VMS behavior of \f(CW\*(C`die\*(C'\fR if
either \f(CW$!\fR or \f(CW$?\fR are non-zero, one of those values will be
encoded into a native \s-1VMS\s0 status value.  If both of the \s-1UNIX\s0 status
values are 0, and the \f(CW$^E\fR value is set one of \s-1ERROR\s0 or \s-1SEVERE_ERROR\s0
severity, then the \f(CW$^E\fR value will be used as the exit code as is.
If none of the above apply, the \s-1UNIX\s0 value of 255 will be encoded into
a native \s-1VMS\s0 exit status value.
.Sp
Please note a significant difference in the behavior of \f(CW\*(C`die\*(C'\fR in
the future \s-1POSIX_EXIT\s0 mode is that it does not force a \s-1VMS\s0
\&\s-1SEVERE_ERROR\s0 status on exit.  The \s-1UNIX\s0 exit values of 2 through
255 will be encoded in \s-1VMS\s0 status values with severity levels of
\&\s-1SUCCESS\s0.  The \s-1UNIX\s0 exit value of 1 will be encoded in a \s-1VMS\s0 status
value with a severity level of \s-1ERROR\s0.  This is to be compatible with
how the \s-1VMS\s0 C library encodes these values.
.Sp
The minimum severity level set by \f(CW\*(C`die\*(C'\fR in a future \s-1POSIX_EXIT\s0 mode
may be changed to be \s-1ERROR\s0 or higher before that mode becomes fully active
depending on the results of testing and further review.  If this is
done, the behavior of c<\s-1DIE\s0> in the future \s-1POSIX_EXIT\s0 will close enough
to the default mode that most \s-1DCL\s0 shell scripts will probably not notice
a difference.
.Sp
See \f(CW$?\fR for a description of the encoding of the \s-1UNIX\s0 value to
produce a native \s-1VMS\s0 status containing it.
.IP "dump" 4
.IX Item "dump"
Rather than causing Perl to abort and dump core, the \f(CW\*(C`dump\*(C'\fR
operator invokes the \s-1VMS\s0 debugger.  If you continue to
execute the Perl program under the debugger, control will
be transferred to the label specified as the argument to
\&\f(CW\*(C`dump\*(C'\fR, or, if no label was specified, back to the
beginning of the program.  All other state of the program
(\fIe.g.\fR values of variables, open file handles) are not
affected by calling \f(CW\*(C`dump\*(C'\fR.
.IP "exec \s-1LIST\s0" 4
.IX Item "exec LIST"
A call to \f(CW\*(C`exec\*(C'\fR will cause Perl to exit, and to invoke the command
given as an argument to \f(CW\*(C`exec\*(C'\fR via \f(CW\*(C`lib$do_command\*(C'\fR.  If the
argument begins with '@' or '$' (other than as part of a filespec),
then it is executed as a \s-1DCL\s0 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 \fI.Exe\fR and the process
defaults to expand the filespec) and pass the rest of \f(CW\*(C`exec\*(C'\fR'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 \f(CW\*(C`MCR\*(C'\fR or a text file which should be passed to \s-1DCL\s0 as a
command procedure.
.IP "fork" 4
.IX Item "fork"
While in principle the \f(CW\*(C`fork\*(C'\fR operator could be implemented via
(and with the same rather severe limitations as) the \s-1CRTL\s0 \f(CW\*(C`vfork()\*(C'\fR
routine, and while some internal support to do just that is in
place, the implementation has never been completed, making \f(CW\*(C`fork\*(C'\fR
currently unavailable.  A true kernel \f(CW\*(C`fork()\*(C'\fR is expected in a
future version of \s-1VMS\s0, and the pseudo-fork based on interpreter
threads may be available in a future version of Perl on \s-1VMS\s0 (see
perlfork).  In the meantime, use \f(CW\*(C`system\*(C'\fR, backticks, or piped
filehandles to create subprocesses.
.IP "getpwent" 4
.IX Item "getpwent"
.PD 0
.IP "getpwnam" 4
.IX Item "getpwnam"
.IP "getpwuid" 4
.IX Item "getpwuid"
.PD
These operators obtain the information described in perlfunc,
if you have the privileges necessary to retrieve the named user's
\&\s-1UAF\s0 information via \f(CW\*(C`sys$getuai\*(C'\fR.  If not, then only the \f(CW$name\fR,
\&\f(CW$uid\fR, and \f(CW$gid\fR items are returned.  The \f(CW$dir\fR item contains
the login directory in \s-1VMS\s0 syntax, while the \f(CW$comment\fR item
contains the login directory in Unix syntax. The \f(CW$gcos\fR item
contains the owner field from the \s-1UAF\s0 record.  The \f(CW$quota\fR
item is not used.
.IP "gmtime" 4
.IX Item "gmtime"
The \f(CW\*(C`gmtime\*(C'\fR operator will function properly if you have a
working \s-1CRTL\s0 \f(CW\*(C`gmtime()\*(C'\fR routine, or if the logical name
\&\s-1SYS$TIMEZONE_DIFFERENTIAL\s0 is defined as the number of seconds
which must be added to \s-1UTC\s0 to yield local time.  (This logical
name is defined automatically if you are running a version of
\&\s-1VMS\s0 with built-in \s-1UTC\s0 support.)  If neither of these cases is
true, a warning message is printed, and \f(CW\*(C`undef\*(C'\fR is returned.
.IP "kill" 4
.IX Item "kill"
In most cases, \f(CW\*(C`kill\*(C'\fR is implemented via the undocumented system
service <$SIGPRC>, which has the same calling sequence as <$FORCEX>, but
throws an exception in the target process rather than forcing it to call
\&\f(CW$EXIT\fR.  Generally speaking, \f(CW\*(C`kill\*(C'\fR follows the behavior of the
\&\s-1CRTL\s0's \f(CW\*(C`kill()\*(C'\fR function, but unlike that function can be called from
within a signal handler.  Also, unlike the \f(CW\*(C`kill\*(C'\fR in some versions of
the \s-1CRTL\s0, Perl's \f(CW\*(C`kill\*(C'\fR checks the validity of the signal passed in and
returns an error rather than attempting to send an unrecognized signal.
.Sp
Also, negative signal values don't do anything special under
\&\s-1VMS\s0; they're just converted to the corresponding positive value.
.IP "qx//" 4
.IX Item "qx//"
See the entry on \f(CW\*(C`backticks\*(C'\fR above.
.IP "select (system call)" 4
.IX Item "select (system call)"
If Perl was not built with socket support, the system call
version of \f(CW\*(C`select\*(C'\fR is not available at all.  If socket
support is present, then the system call version of
\&\f(CW\*(C`select\*(C'\fR functions only for file descriptors attached
to sockets.  It will not provide information about regular
files or pipes, since the \s-1CRTL\s0 \f(CW\*(C`select()\*(C'\fR routine does not
provide this functionality.
.IP "stat \s-1EXPR\s0" 4
.IX Item "stat EXPR"
Since \s-1VMS\s0 keeps track of files according to a different scheme
than Unix, it's not really possible to represent the file's \s-1ID\s0
in the \f(CW\*(C`st_dev\*(C'\fR and \f(CW\*(C`st_ino\*(C'\fR fields of a \f(CW\*(C`struct stat\*(C'\fR.  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.
.IP "system \s-1LIST\s0" 4
.IX Item "system LIST"
The \f(CW\*(C`system\*(C'\fR operator creates a subprocess, and passes its 
arguments to the subprocess for execution as a \s-1DCL\s0 command.  
Since the subprocess is created directly via \f(CW\*(C`lib$spawn()\*(C'\fR, any 
valid \s-1DCL\s0 command string may be specified.  If the string begins with
\&'@', it is treated as a \s-1DCL\s0 command unconditionally.  Otherwise, if
the first token contains a character used as a delimiter in file
specification (e.g. \f(CW\*(C`:\*(C'\fR or \f(CW\*(C`]\*(C'\fR), an attempt is made to expand it
using  a default type of \fI.Exe\fR and the process defaults, and if
successful, the resulting file is invoked via \f(CW\*(C`MCR\*(C'\fR. This allows you
to invoke an image directly simply by passing the file specification
to \f(CW\*(C`system\*(C'\fR, a common Unixish idiom.  If the token has no file type,
and matches a file with null type, then an attempt is made to
determine whether the file is an executable image which should be
invoked using \f(CW\*(C`MCR\*(C'\fR or a text file which should be passed to \s-1DCL\s0
as a command procedure.
.Sp
If \s-1LIST\s0 consists of the empty string, \f(CW\*(C`system\*(C'\fR spawns an
interactive \s-1DCL\s0 subprocess, in the same fashion as typing
\&\fB\s-1SPAWN\s0\fR at the \s-1DCL\s0 prompt.
.Sp
Perl waits for the subprocess to complete before continuing
execution in the current process.  As described in perlfunc,
the return value of \f(CW\*(C`system\*(C'\fR is a fake \*(L"status\*(R" which follows
\&\s-1POSIX\s0 semantics unless the pragma \f(CW\*(C`use vmsish \*(Aqstatus\*(Aq\*(C'\fR is in
effect; see the description of \f(CW$?\fR in this document for more 
detail.
.IP "time" 4
.IX Item "time"
The value returned by \f(CW\*(C`time\*(C'\fR is the offset in seconds from
01\-JAN\-1970 00:00:00 (just like the \s-1CRTL\s0's \fItimes()\fR routine), in order
to make life easier for code coming in from the POSIX/Unix world.
.IP "times" 4
.IX Item "times"
The array returned by the \f(CW\*(C`times\*(C'\fR operator is divided up 
according to the same rules the \s-1CRTL\s0 \f(CW\*(C`times()\*(C'\fR routine.  
Therefore, the \*(L"system time\*(R" elements will always be 0, since 
there is no difference between \*(L"user time\*(R" and \*(L"system\*(R" time 
under \s-1VMS\s0, and the time accumulated by a subprocess may or may 
not appear separately in the \*(L"child time\*(R" field, depending on 
whether times keeps track of subprocesses separately.  Note
especially that the \s-1VAXCRTL\s0 (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.
.IP "unlink \s-1LIST\s0" 4
.IX Item "unlink LIST"
\&\f(CW\*(C`unlink\*(C'\fR will delete the highest version of a file only; in
order to delete all versions, you need to say
.Sp
.Vb 1
\&    1 while unlink LIST;
.Ve
.Sp
You may need to make this change to scripts written for a
Unix system which expect that after a call to \f(CW\*(C`unlink\*(C'\fR,
no files with the names passed to \f(CW\*(C`unlink\*(C'\fR will exist.
(Note: This can be changed at compile time; if you
\&\f(CW\*(C`use Config\*(C'\fR and \f(CW$Config{\*(Aqd_unlink_all_versions\*(Aq}\fR is
\&\f(CW\*(C`define\*(C'\fR, then \f(CW\*(C`unlink\*(C'\fR will delete all versions of a
file on the first call.)
.Sp
\&\f(CW\*(C`unlink\*(C'\fR will delete a file if at all possible, even if it
requires changing file protection (though it won't try to
change the protection of the parent directory).  You can tell
whether you've got explicit delete access to a file by using the
\&\f(CW\*(C`VMS::Filespec::candelete\*(C'\fR operator.  For instance, in order
to delete only files to which you have delete access, you could
say something like
.Sp
.Vb 8
\&    sub safe_unlink {
\&        my($file,$num);
\&        foreach $file (@_) {
\&            next unless VMS::Filespec::candelete($file);
\&            $num += unlink $file;
\&        }
\&        $num;
\&    }
.Ve
.Sp
(or you could just use \f(CW\*(C`VMS::Stdio::remove\*(C'\fR, if you've installed
the VMS::Stdio extension distributed with Perl). If \f(CW\*(C`unlink\*(C'\fR has to
change the file protection to delete the file, and you interrupt it
in midstream, the file may be left intact, but with a changed \s-1ACL\s0
allowing you delete access.
.Sp
This behavior of \f(CW\*(C`unlink\*(C'\fR is to be compatible with \s-1POSIX\s0 behavior
and not traditional \s-1VMS\s0 behavior.
.IP "utime \s-1LIST\s0" 4
.IX Item "utime LIST"
This operator changes only the modification time of the file (\s-1VMS\s0 
revision date) on \s-1ODS\-2\s0 volumes and \s-1ODS\-5\s0 volumes without access 
dates enabled. On \s-1ODS\-5\s0 volumes with access dates enabled, the 
true access time is modified.
.IP "waitpid \s-1PID\s0,FLAGS" 4
.IX Item "waitpid PID,FLAGS"
If \s-1PID\s0 is a subprocess started by a piped \f(CW\*(C`open()\*(C'\fR (see open), 
\&\f(CW\*(C`waitpid\*(C'\fR will wait for that subprocess, and return its final status
value in \f(CW$?\fR.  If \s-1PID\s0 is a subprocess created in some other way (e.g.
SPAWNed before Perl was invoked), \f(CW\*(C`waitpid\*(C'\fR will simply check once per
second whether the process has completed, and return when it has.  (If
\&\s-1PID\s0 specifies a process that isn't a subprocess of the current process,
and you invoked Perl with the \f(CW\*(C`\-w\*(C'\fR switch, a warning will be issued.)
.Sp
Returns \s-1PID\s0 on success, \-1 on error.  The \s-1FLAGS\s0 argument is ignored
in all cases.
.SH "Perl variables"
.IX Header "Perl variables"
The following VMS-specific information applies to the indicated
\&\*(L"special\*(R" Perl variables, in addition to the general information
in perlvar.  Where there is a conflict, this information
takes precedence.
.ie n .IP "%ENV" 4
.el .IP "\f(CW%ENV\fR" 4
.IX Item "%ENV"
The operation of the \f(CW%ENV\fR array depends on the translation
of the logical name \fI\s-1PERL_ENV_TABLES\s0\fR.  If defined, it should
be a search list, each element of which specifies a location
for \f(CW%ENV\fR elements.  If you tell Perl to read or set the
element \f(CW\*(C`$ENV{\*(C'\fR\fIname\fR\f(CW\*(C`}\*(C'\fR, then Perl uses the translations of
\&\fI\s-1PERL_ENV_TABLES\s0\fR as follows:
.RS 4
.IP "\s-1CRTL_ENV\s0" 4
.IX Item "CRTL_ENV"
This string tells Perl to consult the \s-1CRTL\s0's internal \f(CW\*(C`environ\*(C'\fR
array of key-value pairs, using \fIname\fR as the key.  In most cases,
this contains only a few keys, but if Perl was invoked via the C
\&\f(CW\*(C`exec[lv]e()\*(C'\fR function, as is the case for \s-1CGI\s0 processing by some
\&\s-1HTTP\s0 servers, then the \f(CW\*(C`environ\*(C'\fR array may have been populated by
the calling program.
.IP "CLISYM_[\s-1LOCAL\s0]" 4
.IX Item "CLISYM_[LOCAL]"
A string beginning with \f(CW\*(C`CLISYM_\*(C'\fRtells Perl to consult the \s-1CLI\s0's
symbol tables, using \fIname\fR as the name of the symbol.  When reading
an element of \f(CW%ENV\fR, the local symbol table is scanned first, followed
by the global symbol table..  The characters following \f(CW\*(C`CLISYM_\*(C'\fR are
significant when an element of \f(CW%ENV\fR is set or deleted: if the
complete string is \f(CW\*(C`CLISYM_LOCAL\*(C'\fR, the change is made in the local
symbol table; otherwise the global symbol table is changed.