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

VERSION
    version 0.30

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 internally for "tee". By default,
    Capture::Tiny will timeout with an error if such 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. B<NOTE>, this does not timeout the code
    reference being captured -- this only prevents Capture::Tiny itself from
    hanging your process waiting for its child processes to be ready to
    proceed.

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>

CONTRIBUTORS
    *   Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>

    *   David E. Wheeler <david@justatheory.com>

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

