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

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

	   $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;

       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)

       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

       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
	   Like	Open3 but without STDERR capture.

	   This	is a CPAN module that has better error handling	and more
	   facilities than Open3.

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

perl v5.26.0			  2017-04-19			 IPC::Open3(3)


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