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

version 0.11

   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
   };

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.

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

   ($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 ...
   };

   $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.

   ($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.

   $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.

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.

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.

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.

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.

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.

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

It's just too buggy when it comes to layers and UTF8.

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.

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

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.

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

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. You will be automatically notified of any progress on the request by the system.

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

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

David Golden <dagolden@cpan.org>

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

This is free software, licensed under:

  The Apache License, Version 2.0, January 2004