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IPC::Run(3pm)	      User Contributed Perl Documentation	 IPC::Run(3pm)

NAME
       IPC::Run - system() and background procs w/ piping, redirs, ptys (Unix,
       Win32)

SYNOPSIS
	  ## First,a command to run:
	     my @cat = qw( cat );

	  ## Using run() instead of system():
	     use IPC::Run qw( run timeout );

	     run \@cmd, \$in, \$out, \$err, timeout( 10 ) or die "cat: $?"

	     # Can do I/O to sub refs and filenames, too:
	     run \@cmd, '<', "in.txt", \&out, \&err or die "cat: $?"
	     run \@cat, '<', "in.txt", '>>', "out.txt", '2>>', "err.txt";

	     # Redirecting using psuedo-terminals instad of pipes.
	     run \@cat, '<pty<', \$in,	'>pty>', \$out_and_err;

	  ## Scripting subprocesses (like Expect):

	     use IPC::Run qw( start pump finish timeout );

	     # Incrementally read from / write to scalars.
	     # $in is drained as it is fed to cat's stdin,
	     # $out accumulates cat's stdout
	     # $err accumulates cat's stderr
	     # $h is for "harness".
	     my $h = start \@cat, \$in, \$out, \$err, timeout( 10 );

	     $in .= "some input\n";
	     pump $h until $out =~ /input\n/g;

	     $in .= "some more input\n";
	     pump $h until $out =~ /\G.*more input\n/;

	     $in .= "some final input\n";
	     finish $h or die "cat returned $?";

	     warn $err if $err;
	     print $out;	 ## All of cat's output

	  # Piping between children
	     run \@cat, '|', \@gzip;

	  # Multiple children simultaneously (run() blocks until all
	  # children exit, use start() for background execution):
	     run \@foo1, '&', \@foo2;

	  # Calling \&set_up_child in the child before it executes the
	  # command (only works on systems with true fork() & exec())
	  # exceptions thrown in set_up_child() will be propagated back
	  # to the parent and thrown from run().
	     run \@cat, \$in, \$out,
		init => \&set_up_child;

	  # Read from / write to file handles you open and close
	     open IN,  '<in.txt'  or die $!;
	     open OUT, '>out.txt' or die $!;
	     print OUT "preamble\n";
	     run \@cat, \*IN, \*OUT or die "cat returned $?";
	     print OUT "postamble\n";
	     close IN;
	     close OUT;

	  # Create pipes for you to read / write (like IPC::Open2 & 3).
	     $h = start
		\@cat,
		   '<pipe', \*IN,
		   '>pipe', \*OUT,
		   '2>pipe', \*ERR
		or die "cat returned $?";
	     print IN "some input\n";
	     close IN;
	     print <OUT>, <ERR>;
	     finish $h;

	  # Mixing input and output modes
	     run \@cat, 'in.txt', \&catch_some_out, \*ERR_LOG );

	  # Other redirection constructs
	     run \@cat, '>&', \$out_and_err;
	     run \@cat, '2>&1';
	     run \@cat, '0<&3';
	     run \@cat, '<&-';
	     run \@cat, '3<', \$in3;
	     run \@cat, '4>', \$out4;
	     # etc.

	  # Passing options:
	     run \@cat, 'in.txt', debug => 1;

	  # Call this system's shell, returns TRUE on 0 exit code
	  # THIS IS THE OPPOSITE SENSE OF system()'s RETURN VALUE
	     run "cat a b c" or die "cat returned $?";

	  # Launch a sub process directly, no shell.  Can't do redirection
	  # with this form, it's here to behave like system() with an
	  # inverted result.
	     $r = run "cat a b c";

	  # Read from a file in to a scalar
	     run io( "filename", 'r', \$recv );
	     run io( \*HANDLE,	 'r', \$recv );

DESCRIPTION
       IPC::Run allows you to run and interact with child processes using
       files, pipes, and pseudo-ttys.  Both system()-style and scripted usages
       are supported and may be mixed.	Likewise, functional and OO API styles
       are both supported and may be mixed.

       Various redirection operators reminiscent of those seen on common Unix
       and DOS command lines are provided.

       Before digging in to the details a few LIMITATIONS are important enough
       to be mentioned right up front:

       Win32 Support
	   Win32 support is working but EXPERIMENTAL, but does pass all
	   relevant tests on NT 4.0.  See "Win32 LIMITATIONS".

       pty Support
	   If you need pty support, IPC::Run should work well enough most of
	   the time, but IO::Pty is being improved, and IPC::Run will be
	   improved to use IO::Pty's new features when it is release.

	   The basic problem is that the pty needs to initialize itself before
	   the parent writes to the master pty, or the data written gets lost.
	   So IPC::Run does a sleep(1) in the parent after forking to
	   (hopefully) give the child a chance to run.	This is a kludge that
	   works well on non heavily loaded systems :(.

	   ptys are not supported yet under Win32, but will be emulated...

       Debugging Tip
	   You may use the environment variable "IPCRUNDEBUG" to see what's
	   going on under the hood:

	      $ IPCRUNDEBUG=basic   myscript	 # prints minimal debugging
	      $ IPCRUNDEBUG=data    myscript	 # prints all data reads/writes
	      $ IPCRUNDEBUG=details myscript	 # prints lots of low-level details
	      $ IPCRUNDEBUG=gory    myscript	 # (Win32 only) prints data moving through
						 # the helper processes.

       We now return you to your regularly scheduled documentation.

   Harnesses
       Child processes and I/O handles are gathered in to a harness, then
       started and run until the processing is finished or aborted.

   run() vs. start(); pump(); finish();
       There are two modes you can run harnesses in: run() functions as an
       enhanced system(), and start()/pump()/finish() allow for background
       processes and scripted interactions with them.

       When using run(), all data to be sent to the harness is set up in
       advance (though one can feed subprocesses input from subroutine refs to
       get around this limitation). The harness is run and all output is
       collected from it, then any child processes are waited for:

	  run \@cmd, \<<IN, \$out;
	  blah
	  IN

	  ## To precompile harnesses and run them later:
	  my $h = harness \@cmd, \<<IN, \$out;
	  blah
	  IN

	  run $h;

       The background and scripting API is provided by start(), pump(), and
       finish(): start() creates a harness if need be (by calling harness())
       and launches any subprocesses, pump() allows you to poll them for
       activity, and finish() then monitors the harnessed activities until
       they complete.

	  ## Build the harness, open all pipes, and launch the subprocesses
	  my $h = start \@cat, \$in, \$out;
	  $in = "first input\n";

	  ## Now do I/O.  start() does no I/O.
	  pump $h while length $in;  ## Wait for all input to go

	  ## Now do some more I/O.
	  $in = "second input\n";
	  pump $h until $out =~ /second input/;

	  ## Clean up
	  finish $h or die "cat returned $?";

       You can optionally compile the harness with harness() prior to
       start()ing or run()ing, and you may omit start() between harness() and
       pump().	You might want to do these things if you compile your
       harnesses ahead of time.

   Using regexps to match output
       As shown in most of the scripting examples, the read-to-scalar facility
       for gathering subcommand's output is often used with regular
       expressions to detect stopping points.  This is because subcommand
       output often arrives in dribbles and drabs, often only a character or
       line at a time.	This output is input for the main program and piles up
       in variables like the $out and $err in our examples.

       Regular expressions can be used to wait for appropriate output in
       several ways.  The "cat" example in the previous section demonstrates
       how to pump() until some string appears in the output.  Here's an
       example that uses "smb" to fetch files from a remote server:

	  $h = harness \@smbclient, \$in, \$out;

	  $in = "cd /src\n";
	  $h->pump until $out =~ /^smb.*> \Z/m;
	  die "error cding to /src:\n$out" if $out =~ "ERR";
	  $out = '';

	  $in = "mget *\n";
	  $h->pump until $out =~ /^smb.*> \Z/m;
	  die "error retrieving files:\n$out" if $out =~ "ERR";

	  $in = "quit\n";
	  $h->finish;

       Notice that we carefully clear $out after the first command/response
       cycle? That's because IPC::Run does not delete $out when we continue,
       and we don't want to trip over the old output in the second
       command/response cycle.

       Say you want to accumulate all the output in $out and analyze it
       afterwards.  Perl offers incremental regular expression matching using
       the "m//gc" and pattern matching idiom and the "\G" assertion.
       IPC::Run is careful not to disturb the current "pos()" value for
       scalars it appends data to, so we could modify the above so as not to
       destroy $out by adding a couple of "/gc" modifiers.  The "/g" keeps us
       from tripping over the previous prompt and the "/c" keeps us from
       resetting the prior match position if the expected prompt doesn't
       materialize immediately:

	  $h = harness \@smbclient, \$in, \$out;

	  $in = "cd /src\n";
	  $h->pump until $out =~ /^smb.*> \Z/mgc;
	  die "error cding to /src:\n$out" if $out =~ "ERR";

	  $in = "mget *\n";
	  $h->pump until $out =~ /^smb.*> \Z/mgc;
	  die "error retrieving files:\n$out" if $out =~ "ERR";

	  $in = "quit\n";
	  $h->finish;

	  analyze( $out );

       When using this technique, you may want to preallocate $out to have
       plenty of memory or you may find that the act of growing $out each time
       new input arrives causes an "O(length($out)^2)" slowdown as $out grows.
       Say we expect no more than 10,000 characters of input at the most.  To
       preallocate memory to $out, do something like:

	  my $out = "x" x 10_000;
	  $out = "";

       "perl" will allocate at least 10,000 characters' worth of space, then
       mark the $out as having 0 length without freeing all that yummy RAM.

   Timeouts and Timers
       More than likely, you don't want your subprocesses to run forever, and
       sometimes it's nice to know that they're going a little slowly.
       Timeouts throw exceptions after a some time has elapsed, timers merely
       cause pump() to return after some time has elapsed.  Neither is
       reset/restarted automatically.

       Timeout objects are created by calling timeout( $interval ) and passing
       the result to run(), start() or harness().  The timeout period starts
       ticking just after all the child processes have been fork()ed or
       spawn()ed, and are polled for expiration in run(), pump() and finish().
       If/when they expire, an exception is thrown.  This is typically useful
       to keep a subprocess from taking too long.

       If a timeout occurs in run(), all child processes will be terminated
       and all file/pipe/ptty descriptors opened by run() will be closed.
       File descriptors opened by the parent process and passed in to run()
       are not closed in this event.

       If a timeout occurs in pump(), pump_nb(), or finish(), it's up to you
       to decide whether to kill_kill() all the children or to implement some
       more graceful fallback.	No I/O will be closed in pump(), pump_nb() or
       finish() by such an exception (though I/O is often closed down in those
       routines during the natural course of events).

       Often an exception is too harsh.	 timer( $interval ) creates timer
       objects that merely prevent pump() from blocking forever.  This can be
       useful for detecting stalled I/O or printing a soothing message or "."
       to pacify an anxious user.

       Timeouts and timers can both be restarted at any time using the timer's
       start() method (this is not the start() that launches subprocesses).
       To restart a timer, you need to keep a reference to the timer:

	  ## Start with a nice long timeout to let smbclient connect.  If
	  ## pump or finish take too long, an exception will be thrown.

	my $h;
	eval {
	  $h = harness \@smbclient, \$in, \$out, \$err, ( my $t = timeout 30 );
	  sleep 11;  # No effect: timer not running yet

	  start $h;
	  $in = "cd /src\n";
	  pump $h until ! length $in;

	  $in = "ls\n";
	  ## Now use a short timeout, since this should be faster
	  $t->start( 5 );
	  pump $h until ! length $in;

	  $t->start( 10 );  ## Give smbclient a little while to shut down.
	  $h->finish;
	};
	if ( $@ ) {
	  my $x = $@;	 ## Preserve $@ in case another exception occurs
	  $h->kill_kill; ## kill it gently, then brutally if need be, or just
			  ## brutally on Win32.
	  die $x;
	}

       Timeouts and timers are not checked once the subprocesses are shut
       down; they will not expire in the interval between the last valid
       process and when IPC::Run scoops up the processes' result codes, for
       instance.

   Spawning synchronization, child exception propagation
       start() pauses the parent until the child executes the command or CODE
       reference and propagates any exceptions thrown (including exec()
       failure) back to the parent.  This has several pleasant effects: any
       exceptions thrown in the child, including exec() failure, come flying
       out of start() or run() as though they had ocurred in the parent.

       This includes exceptions your code thrown from init subs.  In this
       example:

	  eval {
	     run \@cmd, init => sub { die "blast it! foiled again!" };
	  };
	  print $@;

       the exception "blast it! foiled again" will be thrown from the child
       process (preventing the exec()) and printed by the parent.

       In situations like

	  run \@cmd1, "|", \@cmd2, "|", \@cmd3;

       @cmd1 will be initted and exec()ed before @cmd2, and @cmd2 before
       @cmd3.  This can save time and prevent oddball errors emitted by later
       commands when earlier commands fail to execute.	Note that IPC::Run
       doesn't start any commands unless it can find the executables
       referenced by all commands.  These executables must pass both the "-f"
       and "-x" tests described in perlfunc.

       Another nice effect is that init() subs can take their time doing
       things and there will be no problems caused by a parent continuing to
       execute before a child's init() routine is complete.  Say the init()
       routine needs to open a socket or a temp file that the parent wants to
       connect to; without this synchronization, the parent will need to
       implement a retry loop to wait for the child to run, since often, the
       parent gets a lot of things done before the child's first timeslice is
       allocated.

       This is also quite necessary for pseudo-tty initialization, which needs
       to take place before the parent writes to the child via pty.  Writes
       that occur before the pty is set up can get lost.

       A final, minor, nicety is that debugging output from the child will be
       emitted before the parent continues on, making for much clearer
       debugging output in complex situations.

       The only drawback I can conceive of is that the parent can't continue
       to operate while the child is being initted.  If this ever becomes a
       problem in the field, we can implement an option to avoid this
       behavior, but I don't expect it to.

       Win32: executing CODE references isn't supported on Win32, see "Win32
       LIMITATIONS" for details.

   Syntax
       run(), start(), and harness() can all take a harness specification as
       input.  A harness specification is either a single string to be passed
       to the systems' shell:

	  run "echo 'hi there'";

       or a list of commands, io operations, and/or timers/timeouts to
       execute.	 Consecutive commands must be separated by a pipe operator '|'
       or an '&'.  External commands are passed in as array references, and,
       on systems supporting fork(), Perl code may be passed in as subs:

	  run \@cmd;
	  run \@cmd1, '|', \@cmd2;
	  run \@cmd1, '&', \@cmd2;
	  run \&sub1;
	  run \&sub1, '|', \&sub2;
	  run \&sub1, '&', \&sub2;

       '|' pipes the stdout of \@cmd1 the stdin of \@cmd2, just like a shell
       pipe.  '&' does not.  Child processes to the right of a '&' will have
       their stdin closed unless it's redirected-to.

       IPC::Run::IO objects may be passed in as well, whether or not child
       processes are also specified:

	  run io( "infile", ">", \$in ), io( "outfile", "<", \$in );

       as can IPC::Run::Timer objects:

	  run \@cmd, io( "outfile", "<", \$in ), timeout( 10 );

       Commands may be followed by scalar, sub, or i/o handle references for
       redirecting child process input & output:

	  run \@cmd,  \undef,		 \$out;
	  run \@cmd,  \$in,		 \$out;
	  run \@cmd1, \&in, '|', \@cmd2, \*OUT;
	  run \@cmd1, \*IN, '|', \@cmd2, \&out;

       This is known as succinct redirection syntax, since run(), start() and
       harness(), figure out which file descriptor to redirect and how.	 File
       descriptor 0 is presumed to be an input for the child process, all
       others are outputs.  The assumed file descriptor always starts at 0,
       unless the command is being piped to, in which case it starts at 1.

       To be explicit about your redirects, or if you need to do more complex
       things, there's also a redirection operator syntax:

	  run \@cmd, '<', \undef, '>',	\$out;
	  run \@cmd, '<', \undef, '>&', \$out_and_err;
	  run(
	     \@cmd1,
		'<', \$in,
	     '|', \@cmd2,
		\$out
	  );

       Operator syntax is required if you need to do something other than
       simple redirection to/from scalars or subs, like duping or closing file
       descriptors or redirecting to/from a named file.	 The operators are
       covered in detail below.

       After each \@cmd (or \&foo), parsing begins in succinct mode and
       toggles to operator syntax mode when an operator (ie plain scalar, not
       a ref) is seen.	Once in operator syntax mode, parsing only reverts to
       succinct mode when a '|' or '&' is seen.

       In succinct mode, each parameter after the \@cmd specifies what to do
       with the next highest file descriptor. These File descriptor start with
       0 (stdin) unless stdin is being piped to ("'|', \@cmd"), in which case
       they start with 1 (stdout).  Currently, being on the left of a pipe
       ("\@cmd, \$out, \$err, '|'") does not cause stdout to be skipped,
       though this may change since it's not as DWIMerly as it could be.  Only
       stdin is assumed to be an input in succinct mode, all others are
       assumed to be outputs.

       If no piping or redirection is specified for a child, it will inherit
       the parent's open file handles as dictated by your system's close-on-
       exec behavior and the $^F flag, except that processes after a '&' will
       not inherit the parent's stdin. Also note that $^F does not affect file
       desciptors obtained via POSIX, since it only applies to full-fledged
       Perl file handles.  Such processes will have their stdin closed unless
       it has been redirected-to.

       If you want to close a child processes stdin, you may do any of:

	  run \@cmd, \undef;
	  run \@cmd, \"";
	  run \@cmd, '<&-';
	  run \@cmd, '0<&-';

       Redirection is done by placing redirection specifications immediately
       after a command or child subroutine:

	  run \@cmd1,	   \$in, '|', \@cmd2,	   \$out;
	  run \@cmd1, '<', \$in, '|', \@cmd2, '>', \$out;

       If you omit the redirection operators, descriptors are counted starting
       at 0.  Descriptor 0 is assumed to be input, all others are outputs.  A
       leading '|' consumes descriptor 0, so this works as expected.

	  run \@cmd1, \$in, '|', \@cmd2, \$out;

       The parameter following a redirection operator can be a scalar ref, a
       subroutine ref, a file name, an open filehandle, or a closed
       filehandle.

       If it's a scalar ref, the child reads input from or sends output to
       that variable:

	  $in = "Hello World.\n";
	  run \@cat, \$in, \$out;
	  print $out;

       Scalars used in incremental (start()/pump()/finish()) applications are
       treated as queues: input is removed from input scalers, resulting in
       them dwindling to '', and output is appended to output scalars.	This
       is not true of harnesses run() in batch mode.

       It's usually wise to append new input to be sent to the child to the
       input queue, and you'll often want to zap output queues to '' before
       pumping.

	  $h = start \@cat, \$in;
	  $in = "line 1\n";
	  pump $h;
	  $in .= "line 2\n";
	  pump $h;
	  $in .= "line 3\n";
	  finish $h;

       The final call to finish() must be there: it allows the child
       process(es) to run to completion and waits for their exit values.

OBSTINATE CHILDREN
       Interactive applications are usually optimized for human use.  This can
       help or hinder trying to interact with them through modules like
       IPC::Run.  Frequently, programs alter their behavior when they detect
       that stdin, stdout, or stderr are not connected to a tty, assuming that
       they are being run in batch mode.  Whether this helps or hurts depends
       on which optimizations change.  And there's often no way of telling
       what a program does in these areas other than trial and error and,
       occasionally, reading the source.  This includes different versions and
       implementations of the same program.

       All hope is not lost, however.  Most programs behave in reasonably
       tractable manners, once you figure out what it's trying to do.

       Here are some of the issues you might need to be aware of.

       ·   fflush()ing stdout and stderr

	   This lets the user see stdout and stderr immediately.  Many
	   programs undo this optimization if stdout is not a tty, making them
	   harder to manage by things like IPC::Run.

	   Many programs decline to fflush stdout or stderr if they do not
	   detect a tty there.	Some ftp commands do this, for instance.

	   If this happens to you, look for a way to force interactive
	   behavior, like a command line switch or command.  If you can't, you
	   will need to use a pseudo terminal ('<pty<' and '>pty>').

       ·   false prompts

	   Interactive programs generally do not guarantee that output from
	   user commands won't contain a prompt string.	 For example, your
	   shell prompt might be a '$', and a file named '$' might be the only
	   file in a directory listing.

	   This can make it hard to guarantee that your output parser won't be
	   fooled into early termination of results.

	   To help work around this, you can see if the program can alter it's
	   prompt, and use something you feel is never going to occur in
	   actual practice.

	   You should also look for your prompt to be the only thing on a
	   line:

	      pump $h until $out =~ /^<SILLYPROMPT>\s?\z/m;

	   (use "(?!\n)\Z" in place of "\z" on older perls).

	   You can also take the approach that IPC::ChildSafe takes and emit a
	   command with known output after each 'real' command you issue, then
	   look for this known output.	See new_appender() and new_chunker()
	   for filters that can help with this task.

	   If it's not convenient or possibly to alter a prompt or use a known
	   command/response pair, you might need to autodetect the prompt in
	   case the local version of the child program is different then the
	   one you tested with, or if the user has control over the look &
	   feel of the prompt.

       ·   Refusing to accept input unless stdin is a tty.

	   Some programs, for security reasons, will only accept certain types
	   of input from a tty.	 su, notable, will not prompt for a password
	   unless it's connected to a tty.

	   If this is your situation, use a pseudo terminal ('<pty<' and
	   '>pty>').

       ·   Not prompting unless connected to a tty.

	   Some programs don't prompt unless stdin or stdout is a tty.	See if
	   you can turn prompting back on.  If not, see if you can come up
	   with a command that you can issue after every real command and look
	   for it's output, as IPC::ChildSafe does.   There are two filters
	   included with IPC::Run that can help with doing this: appender and
	   chunker (see new_appender() and new_chunker()).

       ·   Different output format when not connected to a tty.

	   Some commands alter their formats to ease machine parsability when
	   they aren't connected to a pipe.  This is actually good, but can be
	   surprising.

PSEUDO TERMINALS
       On systems providing pseudo terminals under /dev, IPC::Run can use
       IO::Pty (available on CPAN) to provide a terminal environment to
       subprocesses.  This is necessary when the subprocess really wants to
       think it's connected to a real terminal.

   CAVEATS
       Psuedo-terminals are not pipes, though they are similar.	 Here are some
       differences to watch out for.

       Echoing
	   Sending to stdin will cause an echo on stdout, which occurs before
	   each line is passed to the child program.  There is currently no
	   way to disable this, although the child process can and should
	   disable it for things like passwords.

       Shutdown
	   IPC::Run cannot close a pty until all output has been collected.
	   This means that it is not possible to send an EOF to stdin by half-
	   closing the pty, as we can when using a pipe to stdin.

	   This means that you need to send the child process an exit command
	   or signal, or run() / finish() will time out.  Be careful not to
	   expect a prompt after sending the exit command.

       Command line editing
	   Some subprocesses, notable shells that depend on the user's prompt
	   settings, will reissue the prompt plus the command line input so
	   far once for each character.

       '>pty>' means '&>pty>', not '1>pty>'
	   The pseudo terminal redirects both stdout and stderr unless you
	   specify a file descriptor.  If you want to grab stderr separately,
	   do this:

	      start \@cmd, '<pty<', \$in, '>pty>', \$out, '2>', \$err;

       stdin, stdout, and stderr not inherited
	   Child processes harnessed to a pseudo terminal have their stdin,
	   stdout, and stderr completely closed before any redirection
	   operators take effect.  This casts of the bonds of the controlling
	   terminal.  This is not done when using pipes.

	   Right now, this affects all children in a harness that has a pty in
	   use, even if that pty would not affect a particular child.  That's
	   a bug and will be fixed.  Until it is, it's best not to mix-and-
	   match children.

   Redirection Operators
	  Operator	 SHNP	Description
	  ========	 ====	===========
	  <, N<		 SHN	Redirects input to a child's fd N (0 assumed)

	  >, N>		 SHN	Redirects output from a child's fd N (1 assumed)
	  >>, N>>	 SHN	Like '>', but appends to scalars or named files
	  >&, &>	 SHN	Redirects stdout & stderr from a child process

	  <pty, N<pty	 S	Like '<', but uses a pseudo-tty instead of a pipe
	  >pty, N>pty	 S	Like '>', but uses a pseudo-tty instead of a pipe

	  N<&M			Dups input fd N to input fd M
	  M>&N			Dups output fd N to input fd M
	  N<&-			Closes fd N

	  <pipe, N<pipe	    P	Pipe opens H for caller to read, write, close.
	  >pipe, N>pipe	    P	Pipe opens H for caller to read, write, close.

       'N' and 'M' are placeholders for integer file descriptor numbers.  The
       terms 'input' and 'output' are from the child process's perspective.

       The SHNP field indicates what parameters an operator can take:

	  S: \$scalar or \&function references.	 Filters may be used with
	     these operators (and only these).
	  H: \*HANDLE or IO::Handle for caller to open, and close
	  N: "file name".
	  P: \*HANDLE opened by IPC::Run as the parent end of a pipe, but read
	     and written to and closed by the caller (like IPC::Open3).

       Redirecting input: [n]<, [n]<pipe
	   You can input the child reads on file descriptor number n to come
	   from a scalar variable, subroutine, file handle, or a named file.
	   If stdin is not redirected, the parent's stdin is inherited.

	      run \@cat, \undef		 ## Closes child's stdin immediately
		 or die "cat returned $?";

	      run \@cat, \$in;

	      run \@cat, \<<TOHERE;
	      blah
	      TOHERE

	      run \@cat, \&input;	## Calls &input, feeding data returned
					 ## to child's.	 Closes child's stdin
					 ## when undef is returned.

	   Redirecting from named files requires you to use the input
	   redirection operator:

	      run \@cat, '<.profile';
	      run \@cat, '<', '.profile';

	      open IN, "<foo";
	      run \@cat, \*IN;
	      run \@cat, *IN{IO};

	   The form used second example here is the safest, since filenames
	   like "0" and "&more\n" won't confuse &run:

	   You can't do either of

	      run \@a, *IN;	 ## INVALID
	      run \@a, '<', *IN; ## BUGGY: Reads file named like "*main::A"

	   because perl passes a scalar containing a string that looks like
	   "*main::A" to &run, and &run can't tell the difference between that
	   and a redirection operator or a file name.  &run guarantees that
	   any scalar you pass after a redirection operator is a file name.

	   If your child process will take input from file descriptors other
	   than 0 (stdin), you can use a redirection operator with any of the
	   valid input forms (scalar ref, sub ref, etc.):

	      run \@cat, '3<', \$in3;

	   When redirecting input from a scalar ref, the scalar ref is used as
	   a queue.  This allows you to use &harness and pump() to feed
	   incremental bits of input to a coprocess.  See "Coprocesses" below
	   for more information.

	   The <pipe operator opens the write half of a pipe on the filehandle
	   glob reference it takes as an argument:

	      $h = start \@cat, '<pipe', \*IN;
	      print IN "hello world\n";
	      pump $h;
	      close IN;
	      finish $h;

	   Unlike the other '<' operators, IPC::Run does nothing further with
	   it: you are responsible for it.  The previous example is
	   functionally equivalent to:

	      pipe( \*R, \*IN ) or die $!;
	      $h = start \@cat, '<', \*IN;
	      print IN "hello world\n";
	      pump $h;
	      close IN;
	      finish $h;

	   This is like the behavior of IPC::Open2 and IPC::Open3.

	   Win32: The handle returned is actually a socket handle, so you can
	   use select() on it.

       Redirecting output: [n]>, [n]>>, [n]>&[m], [n]>pipe
	   You can redirect any output the child emits to a scalar variable,
	   subroutine, file handle, or file name.  You can have &run truncate
	   or append to named files or scalars.	 If you are redirecting stdin
	   as well, or if the command is on the receiving end of a pipeline
	   ('|'), you can omit the redirection operator:

	      @ls = ( 'ls' );
	      run \@ls, \undef, \$out
		 or die "ls returned $?";

	      run \@ls, \undef, \&out;	## Calls &out each time some output
					 ## is received from the child's
					 ## when undef is returned.

	      run \@ls, \undef, '2>ls.err';
	      run \@ls, '2>', 'ls.err';

	   The two parameter form guarantees that the filename will not be
	   interpreted as a redirection operator:

	      run \@ls, '>', "&more";
	      run \@ls, '2>', ">foo\n";

	   You can pass file handles you've opened for writing:

	      open( *OUT, ">out.txt" );
	      open( *ERR, ">err.txt" );
	      run \@cat, \*OUT, \*ERR;

	   Passing a scalar reference and a code reference requires a little
	   more work, but allows you to capture all of the output in a scalar
	   or each piece of output by a callback:

	   These two do the same things:

	      run( [ 'ls' ], '2>', sub { $err_out .= $_[0] } );

	   does the same basic thing as:

	      run( [ 'ls' ], '2>', \$err_out );

	   The subroutine will be called each time some data is read from the
	   child.

	   The >pipe operator is different in concept than the other '>'
	   operators, although it's syntax is similar:

	      $h = start \@cat, $in, '>pipe', \*OUT, '2>pipe', \*ERR;
	      $in = "hello world\n";
	      finish $h;
	      print <OUT>;
	      print <ERR>;
	      close OUT;
	      close ERR;

	   causes two pipe to be created, with one end attached to cat's
	   stdout and stderr, respectively, and the other left open on OUT and
	   ERR, so that the script can manually read(), select(), etc. on
	   them.  This is like the behavior of IPC::Open2 and IPC::Open3.

	   Win32: The handle returned is actually a socket handle, so you can
	   use select() on it.

       Duplicating output descriptors: >&m, n>&m
	   This duplicates output descriptor number n (default is 1 if n is
	   omitted) from descriptor number m.

       Duplicating input descriptors: <&m, n<&m
	   This duplicates input descriptor number n (default is 0 if n is
	   omitted) from descriptor number m

       Closing descriptors: <&-, 3<&-
	   This closes descriptor number n (default is 0 if n is omitted).
	   The following commands are equivalent:

	      run \@cmd, \undef;
	      run \@cmd, '<&-';
	      run \@cmd, '<in.txt', '<&-';

	   Doing

	      run \@cmd, \$in, '<&-';	 ## SIGPIPE recipe.

	   is dangerous: the parent will get a SIGPIPE if $in is not empty.

       Redirecting both stdout and stderr: &>, >&, &>pipe, >pipe&
	   The following pairs of commands are equivalent:

	      run \@cmd, '>&', \$out;	    run \@cmd, '>', \$out,     '2>&1';
	      run \@cmd, '>&', 'out.txt';   run \@cmd, '>', 'out.txt', '2>&1';

	   etc.

	   File descriptor numbers are not permitted to the left or the right
	   of these operators, and the '&' may occur on either end of the
	   operator.

	   The '&>pipe' and '>pipe&' variants behave like the '>pipe'
	   operator, except that both stdout and stderr write to the created
	   pipe.

       Redirection Filters
	   Both input redirections and output redirections that use scalars or
	   subs as endpoints may have an arbitrary number of filter subs
	   placed between them and the child process.  This is useful if you
	   want to receive output in chunks, or if you want to massage each
	   chunk of data sent to the child.  To use this feature, you must use
	   operator syntax:

	      run(
		 \@cmd
		    '<', \&in_filter_2, \&in_filter_1, $in,
		    '>', \&out_filter_1, \&in_filter_2, $out,
	      );

	   This capability is not provided for IO handles or named files.

	   Two filters are provided by IPC::Run: appender and chunker.
	   Because these may take an argument, you need to use the constructor
	   functions new_appender() and new_chunker() rather than using \&
	   syntax:

	      run(
		 \@cmd
		    '<', new_appender( "\n" ), $in,
		    '>', new_chunker, $out,
	      );

   Just doing I/O
       If you just want to do I/O to a handle or file you open yourself, you
       may specify a filehandle or filename instead of a command in the
       harness specification:

	  run io( "filename", '>', \$recv );

	  $h = start io( $io, '>', \$recv );

	  $h = harness \@cmd, '&', io( "file", '<', \$send );

   Options
       Options are passed in as name/value pairs:

	  run \@cat, \$in, debug => 1;

       If you pass the debug option, you may want to pass it in first, so you
       can see what parsing is going on:

	  run debug => 1, \@cat, \$in;

       debug
	   Enables debugging output in parent and child.  Debugging info is
	   emitted to the STDERR that was present when IPC::Run was first
	   "use()"ed (it's "dup()"ed out of the way so that it can be
	   redirected in children without having debugging output emitted on
	   it).

RETURN VALUES
       harness() and start() return a reference to an IPC::Run harness.	 This
       is blessed in to the IPC::Run package, so you may make later calls to
       functions as members if you like:

	  $h = harness( ... );
	  $h->start;
	  $h->pump;
	  $h->finish;

	  $h = start( .... );
	  $h->pump;
	  ...

       Of course, using method call syntax lets you deal with any IPC::Run
       subclasses that might crop up, but don't hold your breath waiting for
       any.

       run() and finish() return TRUE when all subcommands exit with a 0
       result code.  This is the opposite of perl's system() command.

       All routines raise exceptions (via die()) when error conditions are
       recognized.  A non-zero command result is not treated as an error
       condition, since some commands are tests whose results are reported in
       their exit codes.

ROUTINES
	   run Run takes a harness or harness specification and runs it,
	       pumping all input to the child(ren), closing the input pipes
	       when no more input is available, collecting all output that
	       arrives, until the pipes delivering output are closed, then
	       waiting for the children to exit and reaping their result
	       codes.

	       You may think of "run( ... )" as being like

		  start( ... )->finish();

	       , though there is one subtle difference: run() does not set
	       \$input_scalars to '' like finish() does.  If an exception is
	       thrown from run(), all children will be killed off "gently",
	       and then "annihilated" if they do not go gently (in to that
	       dark night. sorry).

	       If any exceptions are thrown, this does a "kill_kill" before
	       propogating them.

	   signal
		  ## To send it a specific signal by name ("USR1"):
		  signal $h, "USR1";
		  $h->signal ( "USR1" );

	       If $signal is provided and defined, sends a signal to all child
	       processes.  Try not to send numeric signals, use "KILL" instead
	       of 9, for instance.  Numeric signals aren't portable.

	       Throws an exception if $signal is undef.

	       This will not clean up the harness, "finish" it if you kill it.

	       Normally TERM kills a process gracefully (this is what the
	       command line utility "kill" does by default), INT is sent by
	       one of the keys "^C", "Backspace" or "<Del>", and "QUIT" is
	       used to kill a process and make it coredump.

	       The "HUP" signal is often used to get a process to "restart",
	       rereading config files, and "USR1" and "USR2" for really
	       application-specific things.

	       Often, running "kill -l" (that's a lower case "L") on the
	       command line will list the signals present on your operating
	       system.

	       WARNING: The signal subsystem is not at all portable.  We *may*
	       offer to simulate "TERM" and "KILL" on some operating systems,
	       submit code to me if you want this.

	       WARNING 2: Up to and including perl v5.6.1, doing almost
	       anything in a signal handler could be dangerous.	 The most safe
	       code avoids all mallocs and system calls, usually by
	       preallocating a flag before entering the signal handler,
	       altering the flag's value in the handler, and responding to the
	       changed value in the main system:

		  my $got_usr1 = 0;
		  sub usr1_handler { ++$got_signal }

		  $SIG{USR1} = \&usr1_handler;
		  while () { sleep 1; print "GOT IT" while $got_usr1--; }

	       Even this approach is perilous if ++ and -- aren't atomic on
	       your system (I've never heard of this on any modern CPU large
	       enough to run perl).

	   kill_kill
		  ## To kill off a process:
		  $h->kill_kill;
		  kill_kill $h;

		  ## To specify the grace period other than 30 seconds:
		  kill_kill $h, grace => 5;

		  ## To send QUIT instead of KILL if a process refuses to die:
		  kill_kill $h, coup_d_grace => "QUIT";

	       Sends a "TERM", waits for all children to exit for up to 30
	       seconds, then sends a "KILL" to any that survived the "TERM".

	       Will wait for up to 30 more seconds for the OS to successfully
	       "KILL" the processes.

	       The 30 seconds may be overridden by setting the "grace" option,
	       this overrides both timers.

	       The harness is then cleaned up.

	       The doubled name indicates that this function may kill again
	       and avoids colliding with the core Perl "kill" function.

	       Returns a 1 if the "TERM" was sufficient, or a 0 if "KILL" was
	       required.  Throws an exception if "KILL" did not permit the
	       children to be reaped.

	       NOTE: The grace period is actually up to 1 second longer than
	       that given.  This is because the granularity of "time" is 1
	       second.	Let me know if you need finer granularity, we can
	       leverage Time::HiRes here.

	       Win32: Win32 does not know how to send real signals, so "TERM"
	       is a full-force kill on Win32.  Thus all talk of grace periods,
	       etc. do not apply to Win32.

	   harness
	       Takes a harness specification and returns a harness.  This
	       harness is blessed in to IPC::Run, allowing you to use method
	       call syntax for run(), start(), et al if you like.

	       harness() is provided so that you can pre-build harnesses if
	       you would like to, but it's not required..

	       You may proceed to run(), start() or pump() after calling
	       harness() (pump() calls start() if need be).  Alternatively,
	       you may pass your harness specification to run() or start() and
	       let them harness() for you.  You can't pass harness
	       specifications to pump(), though.

	   close_terminal
	       This is used as (or in) an init sub to cast off the bonds of a
	       controlling terminal.  It must precede all other redirection
	       ops that affect STDIN, STDOUT, or STDERR to be guaranteed
	       effective.

	   start
		  $h = start(
		     \@cmd, \$in, \$out, ...,
		     timeout( 30, name => "process timeout" ),
		     $stall_timeout = timeout( 10, name => "stall timeout"   ),
		  );

		  $h = start \@cmd, '<', \$in, '|', \@cmd2, ...;

	       start() accepts a harness or harness specification and returns
	       a harness after building all of the pipes and launching (via
	       fork()/exec(), or, maybe someday, spawn()) all the child
	       processes.  It does not send or receive any data on the pipes,
	       see pump() and finish() for that.

	       You may call harness() and then pass it's result to start() if
	       you like, but you only need to if it helps you structure or
	       tune your application.  If you do call harness(), you may skip
	       start() and proceed directly to pump.

	       start() also starts all timers in the harness.  See
	       IPC::Run::Timer for more information.

	       start() flushes STDOUT and STDERR to help you avoid duplicate
	       output.	It has no way of asking Perl to flush all your open
	       filehandles, so you are going to need to flush any others you
	       have open.  Sorry.

	       Here's how if you don't want to alter the state of $| for your
	       filehandle:

		  $ofh = select HANDLE; $of = $|; $| = 1; $| = $of; select $ofh;

	       If you don't mind leaving output unbuffered on HANDLE, you can
	       do the slightly shorter

		  $ofh = select HANDLE; $| = 1; select $ofh;

	       Or, you can use IO::Handle's flush() method:

		  use IO::Handle;
		  flush HANDLE;

	       Perl needs the equivalent of C's fflush( (FILE *)NULL ).

	   adopt
	       Experimental feature. NOT FUNCTIONAL YET, NEED TO CLOSE FDS
	       BETTER IN CHILDREN.  SEE t/adopt.t for a test suite.

	   pump
		  pump $h;
		  $h->pump;

	       Pump accepts a single parameter harness.	 It blocks until it
	       delivers some input or recieves some output.  It returns TRUE
	       if there is still input or output to be done, FALSE otherwise.

	       pump() will automatically call start() if need be, so you may
	       call harness() then proceed to pump() if that helps you
	       structure your application.

	       If pump() is called after all harnessed activities have
	       completed, a "process ended prematurely" exception to be
	       thrown.	This allows for simple scripting of external
	       applications without having to add lots of error handling code
	       at each step of the script:

		  $h = harness \@smbclient, \$in, \$out, $err;

		  $in = "cd /foo\n";
		  $h->pump until $out =~ /^smb.*> \Z/m;
		  die "error cding to /foo:\n$out" if $out =~ "ERR";
		  $out = '';

		  $in = "mget *\n";
		  $h->pump until $out =~ /^smb.*> \Z/m;
		  die "error retrieving files:\n$out" if $out =~ "ERR";

		  $h->finish;

		  warn $err if $err;

	   pump_nb
		  pump_nb $h;
		  $h->pump_nb;

	       "pump() non-blocking", pumps if anything's ready to be pumped,
	       returns immediately otherwise.  This is useful if you're doing
	       some long-running task in the foreground, but don't want to
	       starve any child processes.

	   pumpable
	       Returns TRUE if calling pump() won't throw an immediate
	       "process ended prematurely" exception.  This means that there
	       are open I/O channels or active processes. May yield the parent
	       processes' time slice for 0.01 second if all pipes are to the
	       child and all are paused.  In this case we can't tell if the
	       child is dead, so we yield the processor and then attempt to
	       reap the child in a nonblocking way.

	   reap_nb
	       Attempts to reap child processes, but does not block.

	       Does not currently take any parameters, one day it will allow
	       specific children to be reaped.

	       Only call this from a signal handler if your "perl" is recent
	       enough to have safe signal handling (5.6.1 did not, IIRC, but
	       it was beign discussed on perl5-porters).  Calling this (or
	       doing any significant work) in a signal handler on older
	       "perl"s is asking for seg faults.

	   finish
	       This must be called after the last start() or pump() call for a
	       harness, or your system will accumulate defunct processes and
	       you may "leak" file descriptors.

	       finish() returns TRUE if all children returned 0 (and were not
	       signaled and did not coredump, ie ! $?), and FALSE otherwise
	       (this is like run(), and the opposite of system()).

	       Once a harness has been finished, it may be run() or start()ed
	       again, including by pump()s auto-start.

	       If this throws an exception rather than a normal exit, the
	       harness may be left in an unstable state, it's best to kill the
	       harness to get rid of all the child processes, etc.

	       Specifically, if a timeout expires in finish(), finish() will
	       not kill all the children.  Call "<$h-"kill_kill>> in this case
	       if you care.  This differs from the behavior of "run".

	   result
		  $h->result;

	       Returns the first non-zero result code (ie $? >> 8).  See
	       "full_result" to get the $? value for a child process.

	       To get the result of a particular child, do:

		  $h->result( 0 );  # first child's $? >> 8
		  $h->result( 1 );  # second child

	       or

		  ($h->results)[0]
		  ($h->results)[1]

	       Returns undef if no child processes were spawned and no child
	       number was specified.  Throws an exception if an out-of-range
	       child number is passed.

	   results
	       Returns a list of child exit values.  See "full_results" if you
	       want to know if a signal killed the child.

	       Throws an exception if the harness is not in a finished state.

	   full_result
		  $h->full_result;

	       Returns the first non-zero $?.  See "result" to get the first
	       $? >> 8 value for a child process.

	       To get the result of a particular child, do:

		  $h->full_result( 0 );	 # first child's $? >> 8
		  $h->full_result( 1 );	 # second child

	       or

		  ($h->full_results)[0]
		  ($h->full_results)[1]

	       Returns undef if no child processes were spawned and no child
	       number was specified.  Throws an exception if an out-of-range
	       child number is passed.

	   full_results
	       Returns a list of child exit values as returned by "wait".  See
	       "results" if you don't care about coredumps or signals.

	       Throws an exception if the harness is not in a finished state.

FILTERS
       These filters are used to modify input our output between a child
       process and a scalar or subroutine endpoint.

       binary
	      run \@cmd, ">", binary, \$out;
	      run \@cmd, ">", binary, \$out;  ## Any TRUE value to enable
	      run \@cmd, ">", binary 0, \$out;	## Any FALSE value to disable

	   This is a constructor for a "binmode" "filter" that tells IPC::Run
	   to keep the carriage returns that would ordinarily be edited out
	   for you (binmode is usually off).  This is not a real filter, but
	   an option masquerading as a filter.

	   It's not named "binmode" because you're likely to want to call
	   Perl's binmode in programs that are piping binary data around.

       new_chunker
	   This breaks a stream of data in to chunks, based on an optional
	   scalar or regular expression parameter.  The default is the Perl
	   input record separator in $/, which is a newline be default.

	      run \@cmd, '>', new_chunker, \&lines_handler;
	      run \@cmd, '>', new_chunker( "\r\n" ), \&lines_handler;

	   Because this uses $/ by default, you should always pass in a
	   parameter if you are worried about other code (modules, etc)
	   modifying $/.

	   If this filter is last in a filter chain that dumps in to a scalar,
	   the scalar must be set to '' before a new chunk will be written to
	   it.

	   As an example of how a filter like this can be written, here's a
	   chunker that splits on newlines:

	      sub line_splitter {
		 my ( $in_ref, $out_ref ) = @_;

		 return 0 if length $$out_ref;

		 return input_avail && do {
		    while (1) {
		       if ( $$in_ref =~ s/\A(.*?\n)// ) {
			  $$out_ref .= $1;
			  return 1;
		       }
		       my $hmm = get_more_input;
		       unless ( defined $hmm ) {
			  $$out_ref = $$in_ref;
			  $$in_ref = '';
			  return length $$out_ref ? 1 : 0;
		       }
		       return 0 if $hmm eq 0;
		    }
		 }
	      };

       new_appender
	   This appends a fixed string to each chunk of data read from the
	   source scalar or sub.  This might be useful if you're writing
	   commands to a child process that always must end in a fixed string,
	   like "\n":

	      run( \@cmd,
		 '<', new_appender( "\n" ), \&commands,
	      );

	   Here's a typical filter sub that might be created by
	   new_appender():

	      sub newline_appender {
		 my ( $in_ref, $out_ref ) = @_;

		 return input_avail && do {
		    $$out_ref = join( '', $$out_ref, $$in_ref, "\n" );
		    $$in_ref = '';
		    1;
		 }
	      };

       new_string_source
	   TODO: Needs confirmation. Was previously undocumented. in this
	   module.

	   This is a filter which is exportable. Returns a sub which appends
	   the data passed in to the output buffer and returns 1 if data was
	   appended. 0 if it was an empty string and undef if no data was
	   passed.

	   NOTE: Any additional variables passed to new_string_source will be
	   passed to the sub every time it's called and appended to the
	   output.

       new_string_sink
	   TODO: Needs confirmation. Was previously undocumented.

	   This is a filter which is exportable. Returns a sub which pops the
	   data out of the input stream and pushes it onto the string.

       io  Takes a filename or filehandle, a redirection operator, optional
	   filters, and a source or destination (depends on the redirection
	   operator).  Returns an IPC::Run::IO object suitable for
	   harness()ing (including via start() or run()).

	   This is shorthand for

	      require IPC::Run::IO;

		 ... IPC::Run::IO->new(...) ...

       timer
	      $h = start( \@cmd, \$in, \$out, $t = timer( 5 ) );

	      pump $h until $out =~ /expected stuff/ || $t->is_expired;

	   Instantiates a non-fatal timer.  pump() returns once each time a
	   timer expires.  Has no direct effect on run(), but you can pass a
	   subroutine to fire when the timer expires.

	   See "timeout" for building timers that throw exceptions on
	   expiration.

	   See "timer" in IPC::Run::Timer for details.

       timeout
	      $h = start( \@cmd, \$in, \$out, $t = timeout( 5 ) );

	      pump $h until $out =~ /expected stuff/;

	   Instantiates a timer that throws an exception when it expires.  If
	   you don't provide an exception, a default exception that matches
	   /^IPC::Run: .*timed out/ is thrown by default.  You can pass in
	   your own exception scalar or reference:

	      $h = start(
		 \@cmd, \$in, \$out,
		 $t = timeout( 5, exception => 'slowpoke' ),
	      );

	   or set the name used in debugging message and in the default
	   exception string:

	      $h = start(
		 \@cmd, \$in, \$out,
		 timeout( 50, name => 'process timer' ),
		 $stall_timer = timeout( 5, name => 'stall timer' ),
	      );

	      pump $h until $out =~ /started/;

	      $in = 'command 1';
	      $stall_timer->start;
	      pump $h until $out =~ /command 1 finished/;

	      $in = 'command 2';
	      $stall_timer->start;
	      pump $h until $out =~ /command 2 finished/;

	      $in = 'very slow command 3';
	      $stall_timer->start( 10 );
	      pump $h until $out =~ /command 3 finished/;

	      $stall_timer->start( 5 );
	      $in = 'command 4';
	      pump $h until $out =~ /command 4 finished/;

	      $stall_timer->reset; # Prevent restarting or expirng
	      finish $h;

	   See "timer" for building non-fatal timers.

	   See "timer" in IPC::Run::Timer for details.

FILTER IMPLEMENTATION FUNCTIONS
       These functions are for use from within filters.

       input_avail
	   Returns TRUE if input is available.	If none is available, then
	   &get_more_input is called and its result is returned.

	   This is usually used in preference to &get_more_input so that the
	   calling filter removes all data from the $in_ref before more data
	   gets read in to $in_ref.

	   "input_avail" is usually used as part of a return expression:

	      return input_avail && do {
		 ## process the input just gotten
		 1;
	      };

	   This technique allows input_avail to return the undef or 0 that a
	   filter normally returns when there's no input to process.  If a
	   filter stores intermediate values, however, it will need to react
	   to an undef:

	      my $got = input_avail;
	      if ( ! defined $got ) {
		 ## No more input ever, flush internal buffers to $out_ref
	      }
	      return $got unless $got;
	      ## Got some input, move as much as need be
	      return 1 if $added_to_out_ref;

       get_more_input
	   This is used to fetch more input in to the input variable.  It
	   returns undef if there will never be any more input, 0 if there is
	   none now, but there might be in the future, and TRUE if more input
	   was gotten.

	   "get_more_input" is usually used as part of a return expression,
	   see "input_avail" for more information.

TODO
       These will be addressed as needed and as time allows.

       Stall timeout.

       Expose a list of child process objects.	When I do this, each child
       process is likely to be blessed into IPC::Run::Proc.

       $kid->abort(), $kid->kill(), $kid->signal( $num_or_name ).

       Write tests for /(full_)?results?/ subs.

       Currently, pump() and run() only work on systems where select() works
       on the filehandles returned by pipe().  This does *not* include
       ActiveState on Win32, although it does work on cygwin under Win32
       (thought the tests whine a bit).	 I'd like to rectify that, suggestions
       and patches welcome.

       Likewise start() only fully works on fork()/exec() machines (well, just
       fork() if you only ever pass perl subs as subprocesses).	 There's some
       scaffolding for calling Open3::spawn_with_handles(), but that's
       untested, and not that useful with limited select().

       Support for "\@sub_cmd" as an argument to a command which gets replaced
       with /dev/fd or the name of a temporary file containing foo's output.
       This is like <(sub_cmd ...) found in bash and csh (IIRC).

       Allow multiple harnesses to be combined as independent sets of
       processes in to one 'meta-harness'.

       Allow a harness to be passed in place of an \@cmd.  This would allow
       multiple harnesses to be aggregated.

       Ability to add external file descriptors w/ filter chains and
       endpoints.

       Ability to add timeouts and timing generators (i.e. repeating
       timeouts).

       High resolution timeouts.

Win32 LIMITATIONS
       Fails on Win9X
	   If you want Win9X support, you'll have to debug it or fund me
	   because I don't use that system any more.  The Win32 subsysem has
	   been extended to use temporary files in simple run() invocations
	   and these may actually work on Win9X too, but I don't have time to
	   work on it.

       May deadlock on Win2K (but not WinNT4 or WinXPPro)
	   Spawning more than one subprocess on Win2K causes a deadlock I
	   haven't figured out yet, but simple uses of run() often work.
	   Passes all tests on WinXPPro and WinNT.

       no support yet for <pty< and >pty>
	   These are likely to be implemented as "<" and ">" with binmode on,
	   not sure.

       no support for file descriptors higher than 2 (stderr)
	   Win32 only allows passing explicit fds 0, 1, and 2.	If you really,
	   really need to pass file handles, us Win32API:: GetOsFHandle() or
	   ::FdGetOsFHandle() to get the integer handle and pass it to the
	   child process using the command line, environment, stdin,
	   intermediary file, or other IPC mechnism.  Then use that handle in
	   the child (Win32API.pm provides ways to reconstitute Perl file
	   handles from Win32 file handles).

       no support for subroutine subprocesses (CODE refs)
	   Can't fork(), so the subroutines would have no context, and
	   closures certainly have no meaning

	   Perhaps with Win32 fork() emulation, this can be supported in a
	   limited fashion, but there are other very serious problems with
	   that: all parent fds get dup()ed in to the thread emulating the
	   forked process, and that keeps the parent from being able to close
	   all of the appropriate fds.

       no support for init => sub {} routines.
	   Win32 processes are created from scratch, there is no way to do an
	   init routine that will affect the running child.  Some limited
	   support might be implemented one day, do chdir() and %ENV changes
	   can be made.

       signals
	   Win32 does not fully support signals.  signal() is likely to cause
	   errors unless sending a signal that Perl emulates, and
	   "kill_kill()" is immediately fatal (there is no grace period).

       helper processes
	   IPC::Run uses helper processes, one per redirected file, to adapt
	   between the anonymous pipe connected to the child and the TCP
	   socket connected to the parent.  This is a waste of resources and
	   will change in the future to either use threads (instead of helper
	   processes) or a WaitForMultipleObjects call (instead of select).
	   Please contact me if you can help with the WaitForMultipleObjects()
	   approach; I haven't figured out how to get at it without C code.

       shutdown pause
	   There seems to be a pause of up to 1 second between when a child
	   program exits and the corresponding sockets indicate that they are
	   closed in the parent.  Not sure why.

       binmode
	   binmode is not supported yet.  The underpinnings are implemented,
	   just ask if you need it.

       IPC::Run::IO
	   IPC::Run::IO objects can be used on Unix to read or write arbitrary
	   files.  On Win32, they will need to use the same helper processes
	   to adapt from non-select()able filehandles to select()able ones (or
	   perhaps WaitForMultipleObjects() will work with them, not sure).

       startup race conditions
	   There seems to be an occasional race condition between child
	   process startup and pipe closings.  It seems like if the child is
	   not fully created by the time CreateProcess returns and we close
	   the TCP socket being handed to it, the parent socket can also get
	   closed.  This is seen with the Win32 pumper applications, not the
	   "real" child process being spawned.

	   I assume this is because the kernel hasn't gotten around to
	   incrementing the reference count on the child's end (since the
	   child was slow in starting), so the parent's closing of the child
	   end causes the socket to be closed, thus closing the parent socket.

	   Being a race condition, it's hard to reproduce, but I encountered
	   it while testing this code on a drive share to a samba box.	In
	   this case, it takes t/run.t a long time to spawn it's chile
	   processes (the parent hangs in the first select for several seconds
	   until the child emits any debugging output).

	   I have not seen it on local drives, and can't reproduce it at will,
	   unfortunately.  The symptom is a "bad file descriptor in select()"
	   error, and, by turning on debugging, it's possible to see that
	   select() is being called on a no longer open file descriptor that
	   was returned from the _socket() routine in Win32Helper.  There's a
	   new confess() that checks for this ("PARENT_HANDLE no longer
	   open"), but I haven't been able to reproduce it (typically).

LIMITATIONS
       On Unix, requires a system that supports "waitpid( $pid, WNOHANG )" so
       it can tell if a child process is still running.

       PTYs don't seem to be non-blocking on some versions of Solaris. Here's
       a test script contributed by Borislav Deianov <borislav@ensim.com> to
       see if you have the problem.  If it dies, you have the problem.

	  #!/usr/bin/perl

	  use IPC::Run qw(run);
	  use Fcntl;
	  use IO::Pty;

	  sub makecmd {
	      return ['perl', '-e',
		      '<STDIN>, print "\n" x '.$_[0].'; while(<STDIN>){last if /end/}'];
	  }

	  #pipe R, W;
	  #fcntl(W, F_SETFL, O_NONBLOCK);
	  #while (syswrite(W, "\n", 1)) { $pipebuf++ };
	  #print "pipe buffer size is $pipebuf\n";
	  my $pipebuf=4096;
	  my $in = "\n" x ($pipebuf * 2) . "end\n";
	  my $out;

	  $SIG{ALRM} = sub { die "Never completed!\n" };

	  print "reading from scalar via pipe...";
	  alarm( 2 );
	  run(makecmd($pipebuf * 2), '<', \$in, '>', \$out);
	  alarm( 0 );
	  print "done\n";

	  print "reading from code via pipe... ";
	  alarm( 2 );
	  run(makecmd($pipebuf * 3), '<', sub { $t = $in; undef $in; $t}, '>', \$out);
	  alarm( 0 );
	  print "done\n";

	  $pty = IO::Pty->new();
	  $pty->blocking(0);
	  $slave = $pty->slave();
	  while ($pty->syswrite("\n", 1)) { $ptybuf++ };
	  print "pty buffer size is $ptybuf\n";
	  $in = "\n" x ($ptybuf * 3) . "end\n";

	  print "reading via pty... ";
	  alarm( 2 );
	  run(makecmd($ptybuf * 3), '<pty<', \$in, '>', \$out);
	  alarm(0);
	  print "done\n";

       No support for ';', '&&', '||', '{ ... }', etc: use perl's, since run()
       returns TRUE when the command exits with a 0 result code.

       Does not provide shell-like string interpolation.

       No support for "cd", "setenv", or "export": do these in an init() sub

	  run(
	     \cmd,
		...
		init => sub {
		   chdir $dir or die $!;
		   $ENV{FOO}='BAR'
		}
	  );

       Timeout calculation does not allow absolute times, or specification of
       days, months, etc.

       WARNING: Function coprocesses ("run \&foo, ...") suffer from two
       limitations.  The first is that it is difficult to close all
       filehandles the child inherits from the parent, since there is no way
       to scan all open FILEHANDLEs in Perl and it both painful and a bit
       dangerous to close all open file descriptors with "POSIX::close()".
       Painful because we can't tell which fds are open at the POSIX level,
       either, so we'd have to scan all possible fds and close any that we
       don't want open (normally "exec()" closes any non-inheritable but we
       don't "exec()" for &sub processes.

       The second problem is that Perl's DESTROY subs and other on-exit
       cleanup gets run in the child process.  If objects are instantiated in
       the parent before the child is forked, the the DESTROY will get run
       once in the parent and once in the child.  When coprocess subs exit,
       POSIX::exit is called to work around this, but it means that objects
       that are still referred to at that time are not cleaned up.  So setting
       package vars or closure vars to point to objects that rely on DESTROY
       to affect things outside the process (files, etc), will lead to bugs.

       I goofed on the syntax: "<pipe" vs. "<pty<" and ">filename" are both
       oddities.

TODO
       Allow one harness to "adopt" another:
	      $new_h = harness \@cmd2;
	      $h->adopt( $new_h );

       Close all filehandles not explicitly marked to stay open.
	   The problem with this one is that there's no good way to scan all
	   open FILEHANDLEs in Perl, yet you don't want child processes
	   inheriting handles willy-nilly.

INSPIRATION
       Well, select() and waitpid() badly needed wrapping, and open3() isn't
       open-minded enough for me.

       The shell-like API inspired by a message Russ Allbery sent to
       perl5-porters, which included:

	  I've thought for some time that it would be
	  nice to have a module that could handle full Bourne shell pipe syntax
	  internally, with fork and exec, without ever invoking a shell.  Something
	  that you could give things like:

	  pipeopen (PIPE, [ qw/cat file/ ], '|', [ 'analyze', @args ], '>&3');

       Message ylln51p2b6.fsf@windlord.stanford.edu, on 2000/02/04.

SUPPORT
       Bugs should always be submitted via the CPAN bug tracker

       http://rt.cpan.org/NoAuth/ReportBug.html?Queue=IPC-Run
       <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=IPC-Run>

       For other issues, contact the maintainer (the first listed author)

AUTHORS
       Adam Kennedy <adamk@cpan.org>

       Barrie Slaymaker <barries@slaysys.com>

COPYRIGHT
       Some parts copyright 2008 - 2009 Adam Kennedy.

       Copyright 1999 Barrie Slaymaker.

       You may distribute under the terms of either the GNU General Public
       License or the Artistic License, as specified in the README file.

perl v5.14.2			  2012-08-30			 IPC::Run(3pm)
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