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IPC::Open3(3pm)        Perl Programmers Reference Guide        IPC::Open3(3pm)
NAME
       IPC::Open3 - open a process for reading, writing, and error handling
       using open3()
SYNOPSIS
           $pid = open3(\*CHLD_IN, \*CHLD_OUT, \*CHLD_ERR,
                           'some cmd and args', 'optarg', ...);
           my($wtr, $rdr, $err);
           use Symbol 'gensym'; $err = gensym;
           $pid = open3($wtr, $rdr, $err,
                           'some cmd and args', 'optarg', ...);
           waitpid( $pid, 0 );
           my $child_exit_status = $? >> 8;
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 filehandle (this means that an autovivified lexical cannot be
       used for the STDERR filehandle, see SYNOPSIS).  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 (such as no such file or permission
       denied), are just reported to CHLD_ERR under Windows and OS/2, as it is
       not possible to trap them.
       If the child process dies for any reason, the next write to CHLD_IN is
       likely to generate a SIGPIPE in the parent, which is fatal by default.
       So you may wish to handle this signal.
       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 "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.
       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 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.
See Also
       IPC::Open2
           Like Open3 but without STDERR capture.
       IPC::Run
           This is a CPAN module that has better error handling and more
           facilities than Open3.
WARNING
       The order of arguments differs from that of open2().
perl v5.26.3                      2018-03-01                   IPC::Open3(3pm)