Capture::Tiny(3p)

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

VERSION
This documentation describes version 0.06.

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.

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>

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

AUTHOR
David A. Golden (DAGOLDEN)

COPYRIGHT AND LICENSE
Copyright (c) 2009 by David A. Golden. All rights reserved.

Licensed under Apache License, Version 2.0 (the "License"). You may not use this file except in compliance with the License. A copy of the License was distributed with this file or you may obtain a copy of the License from http://www.apache.org/licenses/LICENSE-2.0

Files produced as output though the use of this software, shall not be considered Derivative Works, but shall be considered the original work of the Licensor.

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.