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Capture::Tiny(3)      User Contributed Perl Documentation     Capture::Tiny(3)

NAME
       Capture::Tiny - Capture STDOUT and STDERR from Perl, XS or external
       programs

VERSION
       version 0.24

SYNOPSIS
	  use Capture::Tiny ':all';

	  # capture from external command

	  ($stdout, $stderr, $exit) = capture {
	    system( $cmd, @args );
	  };

	  # capture from arbitrary code (Perl or external)

	  ($stdout, $stderr, @result) = capture {
	    # your code here
	  };

	  # capture partial or merged output

	  $stdout = capture_stdout { ... };
	  $stderr = capture_stderr { ... };
	  $merged = capture_merged { ... };

	  # tee output

	  ($stdout, $stderr) = tee {
	    # your code here
	  };

	  $stdout = tee_stdout { ... };
	  $stderr = tee_stderr { ... };
	  $merged = tee_merged { ... };

DESCRIPTION
       Capture::Tiny provides a simple, portable way to capture almost
       anything sent to STDOUT or STDERR, regardless of whether it comes from
       Perl, from XS code or from an external program.	Optionally, output can
       be teed so that it is captured while being passed through to the
       original filehandles.  Yes, it even works on Windows (usually).	Stop
       guessing which of a dozen capturing modules to use in any particular
       situation and just use this one.

USAGE
       The following functions are available.  None are exported by default.

   capture
	  ($stdout, $stderr, @result) = capture \&code;
	  $stdout = capture \&code;

       The "capture" function takes a code reference and returns what is sent
       to STDOUT and STDERR as well as any return values from the code
       reference.  In scalar context, it returns only STDOUT.  If no output
       was received for a filehandle, it returns an empty string for that
       filehandle.  Regardless of calling context, all output is captured --
       nothing is passed to the existing filehandles.

       It is prototyped to take a subroutine reference as an argument. Thus,
       it can be called in block form:

	  ($stdout, $stderr) = capture {
	    # your code here ...
	  };

       Note that the coderef is evaluated in list context.  If you wish to
       force scalar context on the return value, you must use the "scalar"
       keyword.

	  ($stdout, $stderr, $count) = capture {
	    my @list = qw/one two three/;
	    return scalar @list; # $count will be 3
	  };

       Also note that within the coderef, the @_ variable will be empty.  So
       don't use arguments from a surrounding subroutine without copying them
       to an array first:

	  sub wont_work {
	    my ($stdout, $stderr) = capture { do_stuff( @_ ) };	   # WRONG
	    ...
	  }

	  sub will_work {
	    my @args = @_;
	    my ($stdout, $stderr) = capture { do_stuff( @args ) }; # RIGHT
	    ...
	  }

       Captures are normally done to an anonymous temporary filehandle.	 To
       capture via a named file (e.g. to externally monitor a long-running
       capture), provide custom filehandles as a trailing list of option
       pairs:

	  my $out_fh = IO::File->new("out.txt", "w+");
	  my $err_fh = IO::File->new("out.txt", "w+");
	  capture { ... } stdout => $out_fh, stderr => $err_fh;

       The filehandles must be read/write and seekable.	 Modifying the files
       or filehandles during a capture operation will give unpredictable
       results.	 Existing IO layers on them may be changed by the capture.

       When called in void context, "capture" saves memory and time by not
       reading back from the capture handles.

   capture_stdout
	  ($stdout, @result) = capture_stdout \&code;
	  $stdout = capture_stdout \&code;

       The "capture_stdout" function works just like "capture" except only
       STDOUT is captured.  STDERR is not captured.

   capture_stderr
	  ($stderr, @result) = capture_stderr \&code;
	  $stderr = capture_stderr \&code;

       The "capture_stderr" function works just like "capture" except only
       STDERR is captured.  STDOUT is not captured.

   capture_merged
	  ($merged, @result) = capture_merged \&code;
	  $merged = capture_merged \&code;

       The "capture_merged" function works just like "capture" except STDOUT
       and STDERR are merged. (Technically, STDERR is redirected to the same
       capturing handle as STDOUT before executing the function.)

       Caution: STDOUT and STDERR output in the merged result are not
       guaranteed to be properly ordered due to buffering.

   tee
	  ($stdout, $stderr, @result) = tee \&code;
	  $stdout = tee \&code;

       The "tee" function works just like "capture", except that output is
       captured as well as passed on to the original STDOUT and STDERR.

       When called in void context, "tee" saves memory and time by not reading
       back from the capture handles, except when the original STDOUT OR
       STDERR were tied or opened to a scalar handle.

   tee_stdout
	  ($stdout, @result) = tee_stdout \&code;
	  $stdout = tee_stdout \&code;

       The "tee_stdout" function works just like "tee" except only STDOUT is
       teed.  STDERR is not teed (output goes to STDERR as usual).

   tee_stderr
	  ($stderr, @result) = tee_stderr \&code;
	  $stderr = tee_stderr \&code;

       The "tee_stderr" function works just like "tee" except only STDERR is
       teed.  STDOUT is not teed (output goes to STDOUT as usual).

   tee_merged
	  ($merged, @result) = tee_merged \&code;
	  $merged = tee_merged \&code;

       The "tee_merged" function works just like "capture_merged" except that
       output is captured as well as passed on to STDOUT.

       Caution: STDOUT and STDERR output in the merged result are not
       guaranteed to be properly ordered due to buffering.

LIMITATIONS
   Portability
       Portability is a goal, not a guarantee.	"tee" requires fork, except on
       Windows where "system(1, @cmd)" is used instead.	 Not tested on any
       particularly esoteric platforms yet.  See the CPAN Testers Matrix
       <http://matrix.cpantesters.org/?dist=Capture-Tiny> for test result by
       platform.

   PerlIO layers
       Capture::Tiny does it's best to preserve PerlIO layers such as ':utf8'
       or ':crlf' when capturing (only for Perl 5.8.1+) .  Layers should be
       applied to STDOUT or STDERR before the call to "capture" or "tee".
       This may not work for tied filehandles (see below).

   Modifying filehandles before capturing
       Generally speaking, you should do little or no manipulation of the
       standard IO filehandles prior to using Capture::Tiny.  In particular,
       closing, reopening, localizing or tying standard filehandles prior to
       capture may cause a variety of unexpected, undesirable and/or
       unreliable behaviors, as described below.  Capture::Tiny does its best
       to compensate for these situations, but the results may not be what you
       desire.

       Closed filehandles

       Capture::Tiny will work even if STDIN, STDOUT or STDERR have been
       previously closed.  However, since they will be reopened to capture or
       tee output, any code within the captured block that depends on finding
       them closed will, of course, not find them to be closed.	 If they
       started closed, Capture::Tiny will close them again when the capture
       block finishes.

       Note that this reopening will happen even for STDIN or a filehandle not
       being captured to ensure that the filehandle used for capture is not
       opened to file descriptor 0, as this causes problems on various
       platforms.

       Prior to Perl 5.12, closed STDIN combined with PERL_UNICODE=D leaks
       filehandles and also breaks tee() for undiagnosed reasons.  So don't do
       that.

       Localized filehandles

       If code localizes any of Perl's standard filehandles before capturing,
       the capture will affect the localized filehandles and not the original
       ones.  External system calls are not affected by localizing a
       filehandle in Perl and will continue to send output to the original
       filehandles (which will thus not be captured).

       Scalar filehandles

       If STDOUT or STDERR are reopened to scalar filehandles prior to the
       call to "capture" or "tee", then Capture::Tiny will override the output
       filehandle for the duration of the "capture" or "tee" call and then,
       for "tee", send captured output to the output filehandle after the
       capture is complete.  (Requires Perl 5.8)

       Capture::Tiny attempts to preserve the semantics of STDIN opened to a
       scalar reference, but note that external processes will not be able to
       read from such a handle.	 Capture::Tiny tries to ensure that external
       processes will read from the null device instead, but this is not
       guaranteed.

       Tied output filehandles

       If STDOUT or STDERR are tied prior to the call to "capture" or "tee",
       then Capture::Tiny will attempt to override the tie for the duration of
       the "capture" or "tee" call and then send captured output to the tied
       filehandle after the capture is complete.  (Requires Perl 5.8)

       Capture::Tiny may not succeed resending UTF-8 encoded data to a tied
       STDOUT or STDERR filehandle.  Characters may appear as bytes.  If the
       tied filehandle is based on Tie::StdHandle, then Capture::Tiny will
       attempt to determine appropriate layers like ":utf8" from the
       underlying filehandle and do the right thing.

       Tied input filehandle

       Capture::Tiny attempts to preserve the semantics of tied STDIN, but
       this requires Perl 5.8 and is not entirely predictable.	External
       processes will not be able to read from such a handle.

       Unless having STDIN tied is crucial, it may be safest to localize STDIN
       when capturing:

	  my ($out, $err) = do { local *STDIN; capture { ... } };

   Modifying filehandles during a capture
       Attempting to modify STDIN, STDOUT or STDERR during "capture" or "tee"
       is almost certainly going to cause problems.  Don't do that.

   No support for Perl 5.8.0
       It's just too buggy when it comes to layers and UTF-8.  Perl 5.8.1 or
       later is recommended.

   Limited support for Perl 5.6
       Perl 5.6 predates PerlIO.  UTF-8 data may not be captured correctly.

ENVIRONMENT
   PERL_CAPTURE_TINY_TIMEOUT
       Capture::Tiny uses subprocesses for "tee".  By default, Capture::Tiny
       will timeout with an error if the subprocesses are not ready to receive
       data within 30 seconds (or whatever is the value of
       $Capture::Tiny::TIMEOUT).  An alternate timeout may be specified by
       setting the "PERL_CAPTURE_TINY_TIMEOUT" environment variable.  Setting
       it to zero will disable timeouts.

SEE ALSO
       This module was, inspired by IO::CaptureOutput, which provides similar
       functionality without the ability to tee output and with more
       complicated code and API.  IO::CaptureOutput does not handle layers or
       most of the unusual cases described in the "Limitations" section and I
       no longer recommend it.

       There are many other CPAN modules that provide some sort of output
       capture, albeit with various limitations that make them appropriate
       only in particular circumstances.  I'm probably missing some.  The long
       list is provided to show why I felt Capture::Tiny was necessary.

       ·   IO::Capture

       ·   IO::Capture::Extended

       ·   IO::CaptureOutput

       ·   IPC::Capture

       ·   IPC::Cmd

       ·   IPC::Open2

       ·   IPC::Open3

       ·   IPC::Open3::Simple

       ·   IPC::Open3::Utils

       ·   IPC::Run

       ·   IPC::Run::SafeHandles

       ·   IPC::Run::Simple

       ·   IPC::Run3

       ·   IPC::System::Simple

       ·   Tee

       ·   IO::Tee

       ·   File::Tee

       ·   Filter::Handle

       ·   Tie::STDERR

       ·   Tie::STDOUT

       ·   Test::Output

SUPPORT
   Bugs / Feature Requests
       Please report any bugs or feature requests through the issue tracker at
       <https://github.com/dagolden/Capture-Tiny/issues>.  You will be
       notified automatically of any progress on your issue.

   Source Code
       This is open source software.  The code repository is available for
       public review and contribution under the terms of the license.

       <https://github.com/dagolden/Capture-Tiny>

	 git clone https://github.com/dagolden/Capture-Tiny.git

AUTHOR
       David Golden <dagolden@cpan.org>

CONTRIBUTOR
       Dagfinn Ilmari Mannsaaker <ilmari@ilmari.org>

COPYRIGHT AND LICENSE
       This software is Copyright (c) 2009 by David Golden.

       This is free software, licensed under:

	 The Apache License, Version 2.0, January 2004

perl v5.18.2			  2014-02-06		      Capture::Tiny(3)
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