File: Stderr.pm

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package IO::Capture::Stderr;
use strict;
use warnings;
use Carp;
use base qw/IO::Capture/;
use IO::Capture::Tie_STDx;

sub _start {
	my $self = shift;
	$self->line_pointer(1);

	if ( _capture_warn_check() ) {
		$self->{'IO::Capture::handler_save'} = defined $SIG{__WARN__} ? $SIG{__WARN__} : 'DEFAULT';
		$SIG{__WARN__} = sub {print STDERR @_;};
	}
	else {
		$self->{'IO::Capture::handler_save'} = undef;
	}
    tie *STDERR, "IO::Capture::Tie_STDx";
}

sub _retrieve_captured_text {
    my $self = shift;
    my $messages = \@{$self->{'IO::Capture::messages'}};

     @$messages = <STDERR>;
	return 1;
}

sub _check_pre_conditions {
	my $self = shift;

	return unless $self->SUPER::_check_pre_conditions;

	if (tied *STDERR) {
		carp "WARNING: STDERR already tied, unable to capture";
		return;
	}
	return 1;
}

sub _stop {
	my $self = shift;
    untie *STDERR;
	$SIG{__WARN__} = $self->{'IO::Capture::handler_save'} if defined $self->{'IO::Capture::handler_save'};
    return 1;
}

#  _capture_warn_check
#
#  Check to see if SIG{__WARN__} handler should be set to direct output
# from warn() to IO::Capture::Stderr.  
#   There are three things to take into consideration.  
#   
#   1) Is the version of perl less than 5.8?
#      - Before 5.8, there was a bug that caused output from warn() 
#        not to be sent to STDERR if it (STDERR) was tied.
#        So, we need to put a handler in to send warn() text to
#        STDERR so IO::Capture::Stderr will capture it.
#   2) Is there a handler set already?
#      - The default handler for SIG{__WARN__} is to send to STDERR.
#        But, if it is set by the program, it may do otherwise, and
#        we don't want to break that. 
#   3)  FORCE_CAPTURE_WARN => 1
#      - To allow users to override a previous handler that was set on
#        SIG{__WARN__}, there is a variable that can be set.  If set,
#        when there is a handler set on IO::Capture::Stderr startup,
#        it will be saved and a new hander set that captures output to
#        IO::Capture::Stderr.  On stop, it will restore the programs
#        handler.
#      
#
#                    
#    Perl   |  FORCE_CAPTURE_WARN  |  Program has   | Set our own
#    < 5.8  |  is set              |  handler set   | handler
#   --------+----------------------+----------------+------------
#           |                      |                |
#   --------+----------------------+----------------+------------
#      X    |                      |                |     X (1)
#   --------+----------------------+----------------+------------
#           |          X           |                |
#   --------+----------------------+----------------+------------
#      X    |          X           |                |     X (1)
#   --------+----------------------+----------------+------------
#           |                      |        X       |
#   --------+----------------------+----------------+------------
#      X    |                      |        X       |
#   --------+----------------------+----------------+------------
#           |          X           |        X       |     X (2)
#   --------+----------------------+----------------+------------
#      X    |          X           |        X       |     X (2)
#   --------+----------------------+----------------+------------
#     (1) WAR to get around bug
#     (2) Replace programs handler with our own

sub _capture_warn_check {
	my $self = shift;

	if (!defined $SIG{__WARN__} ) {
		return $^V lt v5.8 ? 1 : 0;
	}
	return $self->{'FORCE_CAPTURE_WARN'} ? 1 : 0;
}
1;

__END__

=head1 NAME

C<IO::Capture::Stderr> - Capture all output sent to C<STDERR>

=head1 SYNOPSIS

    use IO::Capture::Stderr;

    $capture = IO::Capture::Stderr->new();

    $capture->start(); 		# STDERR Output captured
    print STDERR "Test Line One\n";
    print STDERR "Test Line Two\n";
    print STDERR "Test Line Three\n";
    $capture->stop();		# STDERR output sent to wherever it was before 'start'

    # In 'scalar context' returns next line
    $line = $capture->read;
    print "$line";         # prints "Test Line One"

    $line = $capture->read;
    print "$line";         # prints "Test Line Two"

    # move line pointer to line 1
    $capture->line_pointer(1);

    $line = $capture->read;
    print "$line";         # prints "Test Line One"

    # Find out current line number
    $current_line_position = $capture->line_pointer;

    # In 'List Context' return an array(list)
    @all_lines = $capture->read;

    # Example 1 - "Using in module tests"
    #  Note: If you don't want to make users install 
    #        the IO::Capture module just for your tests,
    #        you can just install in the t/lib directory
    #        of your module and use the lib pragma in  
    #        your tests. 

    use lib "t/lib";
    use IO::Capture:Stderr;

    use Test::More;

	# Create new capture object.  Showing FORCE_CAPTURE_WARN being cleared
	# for example, but 0 is the default, so you don't need to specify
	# unless you want to set.
    my $capture =  IO::Capture:Stderr->new( {FORCE_CAPTURE_WARN => 0} );
    $capture->start

    # execute with a bad parameter to make sure get
    # an error.

    ok( ! $test("Bad Parameter") );

    $capture->stop();

    

=head1 DESCRIPTION

The module C<IO::Capture::Stderr>, is derived from the abstract class C<IO::Capture>.
See L<IO::Capture>. The purpose of the module (as the name suggests) is to capture 
any output sent to C<STDOUT>.  After the capture is stopped, the STDOUT filehandle 
will be reset to the previous location. E.g., If previously redirected to a file, when 
C<IO::Capture-E<gt>stop> is called, output will start going into that file again.

Note:  This module won't work with the perl function, system(), or any other operation 
       involving a fork().  If you want to capture the output from a system command,
       it is faster to use open() or back-ticks.  

       my $output = `/usr/sbin/ls -l 2>&1`;

=head1 METHODS

=head2 new

=over 4

=item *

Creates a new capture object.  

=item *

An object can be reused as needed, so will only need to do one of these. 

=over 4

=item *

Be aware, any data previously captured will be discarded if a new 
capture session is started.  

=back

=back

=head2 start

=over 4

=item *

Start capturing data into the C<IO::Capture> Object.

=item *

Can B<not> be called on an object that is already capturing.

=item *

Can B<not> be called while STDERR tied to an object.  

=item *

C<undef> will be returned on an error.

=back

=head2 stop

=over 4

=item *

Stop capturing data and point STDERR back to it's previous output location
I.e., untie STDERR

=back

=head2 read

=over 4

=item *

In I<Scalar Context>

=over 4

=item *

Lines are read from the buffer at the position of the C<line_pointer>, 
and the pointer is incremented by one.

    $next_line = $capture->read;

=back

=item *

In I<List Context>

=over 4

=item *

The array is returned.  The C<line_pointer> is not affected.

    @buffer = $capture->read;

=back

=item *

Data lines are returned exactly as they were captured.  You may want 
to use C<chomp> on them if you don't want the end of line character(s)

    while (my $line = $capture->read) {
	chomp $line;
	$cat_line = join '', $cat_line, $line;
    }

=back

=head2 line_pointer

=over 4

=item *

Reads or sets the C<line_pointer>.

    my $current_line = $capture->line_pointer;
    $capture->line_pointer(1);

=back

=head1 ARGUMENTS

Pass any arguments to new() in a single array reference.

   IO::Capture::Stderr->new( {FORCE_CAPTURE_WARN => 1} );

=head2 FORCE_CAPTURE_WARN

=over 4


Normally, IO::Capture::Stderr will capture text from I<warn()> function calls. This is because output
from I<warn()> is normally directed to STDERR.  If you wish to force IO::Capture::Stderr to grab the
text from I<warn()>, set FORCE_CAPTURE_WARN to a 1.  Then C<IO::Capture::Stderr> will save the handle
that C<$SIG{__WARN__}> was set to, redirect it to itself on C<start()>, and then set C<$SIG{__WARN__}> 
back after C<stop()> is called.

=back

=head1 SUB-CLASSING

=head2 Adding Features

If you would like to sub-class this module to add a feature (method) or two,
here is a couple of easy steps. Also see L<IO::Capture::Overview>.

=over 4

=item 1

Give your package a name

    package MyPackage;

=item 2

Use this C<IO::Capture::Stderr> as your base class like this:

    package MyPackage;

    use base qw/IO::Capture::Stderr/;

=item 3

Add your new method like this

    package MyPackage;

    use base qw/IO::Capture::Stderr/;

    sub grep {
	my $self = shift;

	for $line (
    }

=back

=head1 See Also

L<IO::Capture::Overview>

L<IO::Capture>

L<IO::Capture::Stdout>

=head1 AUTHORS

Mark Reynolds
reynolds@sgi.com

Jon Morgan
jmorgan@sgi.com

=head1 COPYRIGHT

Copyright (c) 2003, Mark Reynolds. All Rights Reserved.
This module is free software. It may be used, redistributed
and/or modified under the same terms as Perl itself.

=cut