Man Pages

IPC::Open2(3) - phpMan IPC::Open2(3) - phpMan

Command: man perldoc info search(apropos)  


IPC::Open2(3)          Perl Programmers Reference Guide          IPC::Open2(3)



NAME
       IPC::Open2, open2 - open a process for both reading and writing

SYNOPSIS
           use IPC::Open2;

           $pid = open2(\*CHLD_OUT, \*CHLD_IN, 'some cmd and args');
             # or without using the shell
           $pid = open2(\*CHLD_OUT, \*CHLD_IN, 'some', 'cmd', 'and', 'args');

           # or with handle autovivification
           my($chld_out, $chld_in);
           $pid = open2($chld_out, $chld_in, 'some cmd and args');
             # or without using the shell
           $pid = open2($chld_out, $chld_in, 'some', 'cmd', 'and', 'args');

DESCRIPTION
       The open2() function runs the given $cmd and connects $chld_out for reading and $chld_in for writing.  It's
       what you think should work when you try

           $pid = open(HANDLE, "|cmd args|");

       The write filehandle will have autoflush turned on.

       If $chld_out is a string (that is, a bareword filehandle rather than a glob or a reference) and it begins with
       ">&", then the child will send output directly to that file handle.  If $chld_in is a string that begins with
       "<&", then $chld_in will be closed in the parent, and the child will read from it directly.  In both cases,
       there will be a dup(2) instead of a pipe(2) made.

       If either reader or writer is the null string, this will be replaced by an autogenerated filehandle.  If so,
       you must pass a valid lvalue in the parameter slot so it can be overwritten in the caller, or an exception will
       be raised.

       open2() returns the process ID of the child process.  It doesn't return on failure: it just raises an exception
       matching "/^open2:/".  However, "exec" failures in the child are not detected.  You'll have to trap SIGPIPE
       yourself.

       open2() does not wait for and reap the child process after it exits.  Except for short programs where it's
       acceptable to let the operating system take care of this, you need to do this yourself.  This is normally as
       simple as calling "waitpid $pid, 0" when you're done with the process.  Failing to do this can result in an
       accumulation of defunct or "zombie" processes.  See "waitpid" in perlfunc for more information.

       This whole affair is quite dangerous, as you may block forever.  It assumes it's going to talk to something
       like bc, both writing to it and reading from it.  This is presumably safe because you "know" that commands like
       bc will read a line at a time and output a line at a time.  Programs like sort that read their entire input
       stream first, however, are quite apt to cause deadlock.

       The big problem with this approach is that if you don't have control over source code being run in the child
       process, you can't control what it does with pipe buffering.  Thus you can't just open a pipe to "cat -v" and
       continually read and write a line from it.

       The IO::Pty and Expect modules from CPAN can help with this, as they provide a real tty (well, a pseudo-tty,
       actually), which gets you back to line buffering in the invoked command again.

WARNING
       The order of arguments differs from that of open3().

SEE ALSO
       See IPC::Open3 for an alternative that handles STDERR as well.  This function is really just a wrapper around
       open3().



perl v5.8.8                       2001-09-21                     IPC::Open2(3)