MirOS Manual: IPC::Open3(3p)


IPC::Open3(3p)  Perl Programmers Reference Guide   IPC::Open3(3p)

NAME

     IPC::Open3, open3 - open a process for reading, writing, and
     error handling

SYNOPSIS

         $pid = open3(\*CHLD_IN, \*CHLD_OUT, \*CHLD_ERR,
                         'some cmd and args', 'optarg', ...);

         my($wtr, $rdr, $err);
         $pid = open3($wtr, $rdr, $err,
                         'some cmd and args', 'optarg', ...);

DESCRIPTION

     Extremely similar to open2(), open3() spawns the given $cmd
     and connects CHLD_OUT for reading from the child, CHLD_IN
     for writing to the child, and CHLD_ERR for errors.  If
     CHLD_ERR is false, or the same file descriptor as CHLD_OUT,
     then STDOUT and STDERR of the child are on the same filehan-
     dle.  The CHLD_IN will have autoflush turned on.

     If CHLD_IN begins with "<&", then CHLD_IN will be closed in
     the parent, and the child will read from it directly.  If
     CHLD_OUT or CHLD_ERR begins with ">&", then the child will
     send output directly to that filehandle.  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.

     The filehandles may also be integers, in which case they are
     understood as file descriptors.

     open3() returns the process ID of the child process.  It
     doesn't return on failure: it just raises an exception
     matching "/^open3:/".  However, "exec" failures in the child
     are not detected.  You'll have to trap SIGPIPE yourself.

     Note if you specify "-" as the command, in an analogous
     fashion to "open(FOO, "-|")" the child process will just be
     the forked Perl process rather than an external command.
     This feature isn't yet supported on Win32 platforms.

     open3() 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 "wait-
     pid $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.

perl v5.8.8                2005-02-05                           1

IPC::Open3(3p)  Perl Programmers Reference Guide   IPC::Open3(3p)

     If you try to read from the child's stdout writer and their
     stderr writer, you'll have problems with blocking, which
     means you'll want to use select() or the IO::Select, which
     means you'd best use sysread() instead of readline() for
     normal stuff.

     This is very dangerous, as you may block forever.  It
     assumes it's going to talk to something like bc, both writ-
     ing 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.

WARNING

     The order of arguments differs from that of open2().

perl v5.8.8                2005-02-05                           2

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