1IO::Capture::Overview(3U)ser Contributed Perl DocumentatiIoOn::Capture::Overview(3)
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NAME

6       Overview of "IO::Capture" Module, and classes derived from it.
7

DESCRIPTION

9       The modules in this distribution are designed to allow you to capture
10       and process output sent to STDOUT and/or STDERR.
11
12       I initial created the modules to use in building module tests.  I
13       wanted to be able to intentionally cause errors, and insure the module
14       responded correctly.  E.g., Call a class method without a required
15       argument.  Using IO::Capture keeps the user from seeing these
16       intentional errors when running 'make test'.
17
18       I have also found this useful on occasion in Perl Tk apps, where I
19       wanted to capture output from a Perl module I was using.  I could then
20       capture, then put the text into a log or message window.
21
22       Note:  None of the modules currently distributed will capture from the
23       'system' Perl function, or the like.  It could be done, but generally,
24       if you would like to capture from a system command, you don't need this
25       module, just use the backticks operators.
26
27               my $output = '/usr/bin/ls';
28
29       They are small, lightweight modules.  Instead of designing in a lot of
30       features, we designed it to be easily reusable and adaptable.  A module
31       can be quickly built, that incorporates custom methods, but reuses all
32       existing features of one of the derived classes. See the section on
33       "ADDING FEATURES"  Or, if you need to change the actual capture
34       mechanism, "WRITING YOUR OWN DERIVED CLASS".  (Don't worry, it's a
35       piece of cake)
36

DERIVED CLASSES

38       There are several classes derived from "IO::Capture".
39
40   IO::Capture::Stdout
41       Module to capture "STDOUT" from program.  See IO::Capture::Stdout.
42
43   IO::Capture::Stderr
44       Module to capture "STDERR" from program.  See IO::Capture::Stderr.
45
46   IO::Capture::ErrorMessages
47       This method has been depreciated.  The only difference between this one
48       and Stderr.pm was the trap for WARN.  I found it was fixed in 5.8 so
49       just check in Stderr now.  I.e., Just use Stderr now. It (Stderr) will
50       detect what version of perl you are using, and act accordingly.  The
51       two ("IO::Capture::ErrorMessages" and "IO::Capture::Stderr") are
52       currently identical, and "IO::Capture::ErrorMessages" will be removed
53       in a future release.
54
55       If you would like to add features to any of these, or build your own
56       module using "IO::Capture" as a base, read on.
57

ADDING FEATURES

59       If one of these modules takes care of your problem, install it and have
60       fun!
61
62       But let's say you would like to add a feature to one of the derived
63       classes, say IO::Capture::Stdout.  No need to re-write the whole
64       module, just use it as the base, and write your one feature. Here is a
65       somewhat simplified example.
66
67           #
68           # Example module to add a grep_it method
69           #
70           # Give your package a name
71           package MyPackage;
72
73           #use IO:Capture:Stdout as the base
74           use base 'IO::Capture::Stdout';
75
76           #define your method
77           sub grep_it {
78               my $self = shift;
79               my $string = shift;
80               my @found_lines;
81
82               # Making a ref to the array makes it easier to read  :-)
83               my $arrayref = \@{$self->{'IO::Capture::messages'}};
84
85               for my $line (@$arrayref) {
86                   push @found_lines, $line if $line =~ /$string/;
87               }
88               return wantarray ? @found_lines : scalar(@found_lines);
89           }
90           1;
91
92       Using it in this script
93
94           #!/usr/sbin/perl
95           use strict;
96           use warnings;
97           use MyPackage;
98
99           my $capture = MyPackage->new();
100           $capture->start;
101           print "The quick brown fox jumped over ...";
102           print "garden wall";
103           print "The quick red fox jumped over ...";
104           print "garden wall";
105           $capture->stop;
106           for my $line ($capture->grep_it("fox")) {
107               print "$line\n";
108           }
109
110       Results in
111
112           $ grep_it
113           The quick brown fox jumped over ...
114           The quick red fox jumped over ...
115

WRITING YOUR OWN DERIVED CLASS

117       Before starting your own sub-class, be sure to read through
118       IO::Capture.  Pay special attention to the internal methods that are
119       only defined as abstract methods in "IO::Capture".  For examples, look
120       at the sub-classes included with this distribution.
121       ("IO::Capture::Stdout", "IO:Capture::Stderr".  You can start by copying
122       one of these and using it as a template.  They have the required
123       private methods defined already, and you may very well be able to use
124       them as is.  Change any methods, and add any new ones, as needed.
125
126       For example, here is a commented copy of "IO::Capture::Stderr".
127
128           #
129           # Example module using abstract class IO::Capture
130           #
131           # Change this to give your class it's own name
132           package IO::Capture::Stderr;
133
134           # Make IO::Capture the base class
135           use base qw/IO::Capture/;
136
137           # If using included utility module in '_start()'
138           use IO::Capture::Tie_STDx;
139
140           # Override the three abstract methods needed to make a valid
141           # module. See IO::Capture manpage
142           #  1) _start - Starts the data capture. Is run from public method
143           #     start();
144           #
145           #  2) _retrieve_captured_text() - Move the captured text into the
146           #  object hash key, "IO::Capture::messages". Called by public method
147           #
148           #  3) _stop - Stop the data capture. Called by public method 'stop()'
149           #    after private method '_retrieve_captured_text()' returns.
150           #
151           sub _start {
152               tie *STDERR, "IO::Capture::Tie_STDx";
153           }
154
155           sub _retrieve_captured_text {
156               my $self = shift;
157               # making a reference to it makes it more readable ;-)
158               my $messages = \@{$self->{'IO::Capture::messages'}};
159
160               @$messages = <STDERR>;
161           }
162
163           sub _stop {
164               untie *STDERR;
165                       return 1;
166           }
167           1;
168
169       Lets say you don't want to capture all the text.  You just want to grab
170       the lines that have the word "Error" in them.  The only thing you need
171       to change is _retrieve_captured_text. (Besides the package name)
172
173       Something like:
174
175           sub _retrieve_captured_text {
176               my $self = shift;
177               # making a reference to it makes it more readable ;-)
178               my $messages = \@{$self->{'IO::Capture::messages'}};
179
180               while (<STDERR>) {
181                   push @$messages, $_ if /error/i;
182               }
183           }
184
185       Yes. You could do this easier by just using "IO::Capture::Stderr" as
186       the base and overriding "_retrieve_captured_text" like in "ADDING
187       FEATURES", but hey, we needed an easy example.  :-)
188
189       If you want your class to have arguments that users can pass in, just
190       use the default "new()" method and have the arguments passed in as an
191       anonymous array.  See the "IO::Capture::Stderr" module for an example.
192

BUGS

194       Please report bugs on http://rt.cpan.org/
195

CREDITS

197       Special thanks to  James E Keenan for many bug fixes and tests he
198       provided.
199

AUTHOR

201       Mark Reynolds reynolds<at>sgi.com
202
203       Note: "Change <at" to 'at' sign.>
204
206       Copyright (c) 2003-2005, Mark Reynolds. All Rights Reserved.  This
207       module is free software. It may be used, redistributed and/or modified
208       under the same terms as Perl itself.
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212perl v5.36.0                      2022-07-22          IO::Capture::Overview(3)
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