Capture::Tiny(3p)

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

VERSION
version 0.11

SYNOPSIS
   use Capture::Tiny qw/capture tee capture_merged tee_merged/;

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

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

   $merged = capture_merged {
     # your code here
   };

   $merged = tee_merged {
     # your code here
   };

DESCRIPTION
Capture::Tiny provides a simple, portable way to capture 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 handles. Yes, it even works on Windows. Stop guessing which of a dozen capturing modules to use in any particular situation and just use this one.

This module was heavily inspired by IO::CaptureOutput, which provides similar functionality without the ability to tee output and with more complicated code and API.

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

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

The "capture" function takes a code reference and returns what is sent to STDOUT and STDERR. In scalar context, it returns only STDOUT. If no output was received, returns an empty string. Regardless of context, all output is captured -- nothing is passed to the existing handles.

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 ...
   };

  capture_merged
   $merged = capture_merged \&code;

The "capture_merged" function works just like "capture" except STDOUT and STDERR are merged. (Technically, STDERR is redirected to STDOUT before executing the function.) If no output was received, returns an empty string. As with "capture" it may be called in block form.

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

  tee
   ($stdout, $stderr) = 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. As with "capture" it may be called in block form.

  tee_merged
   $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. As with "capture" it may be called in block form.

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.

  PerlIO layers
Capture::Tiny does it's best to preserve PerlIO layers such as ':utf8' or ':crlf' when capturing. Layers should be applied to STDOUT or STDERR before the call to "capture" or "tee".

  Closed STDIN, STDOUT or STDERR
Capture::Tiny will work even if STDIN, STDOUT or STDERR have been previously closed. However, since they may 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 reclose them again when the capture block finishes.

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

Capture::Tiny attempts to preserve the semantics of STDIN opened to a scalar reference.

  Tied STDIN, STDOUT or STDERR
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 handle after the capture is complete. (Requires Perl 5.8)

Capture::Tiny does not (yet) support resending utf8 encoded data to a tied STDOUT or STDERR handle. Characters will appear as bytes.

Capture::Tiny attempts to preserve the semantics of tied STDIN, but capturing or teeing when STDIN is tied is currently broken on Windows.

  Modifiying STDIN, STDOUT or STDERR 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 UTF8.

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.

BUGS
Please report any bugs or feature requests using the CPAN Request Tracker. Bugs can be submitted through the web interface at http://rt.cpan.org/Dist/Display.html?Queue=Capture-Tiny <http://rt.cpan.org/Dist/Display.html?Queue=Capture-Tiny>

When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.

SEE ALSO
This is a selection of 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 by email to "bug-capture-tiny at rt.cpan.org", or through the web interface at http://rt.cpan.org/Public/Dist/Display.html?Name=Capture-Tiny <http://rt.cpan.org/Public/Dist/Display.html?Name=Capture-Tiny>. You will be automatically notified of any progress on the request by the system.

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

http://github.com/dagolden/capture-tiny/tree <http://github.com/dagolden/capture-tiny/tree>

  git clone git://github.com/dagolden/capture-tiny.git

AUTHOR
David Golden <dagolden@cpan.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