1File::Comments(3)     User Contributed Perl Documentation    File::Comments(3)
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NAME

6       File::Comments - Recognizes file formats and extracts format-specific
7       comments
8

SYNOPSIS

10           use File::Comments;
11
12           my $snoop = File::Comments->new();
13
14               # *----------------
15               # | program.c:
16               # | /* comment */
17               # | main () {}
18               # *----------------
19           my $comments = $snoop->comments("program.c");
20               # => [" comment "]
21
22               # *----------------
23               # | script.pl:
24               # | # comment
25               # | print "howdy!\n"; # another comment
26               # *----------------
27           my $comments = $snoop->comments("script.pl");
28               # => [" comment", " another comment"]
29
30               # or strip comments from a file:
31           my $stripped = $snoop->stripped("script.pl");
32               # => "print "howdy!\n";"
33
34               # or just guess a file's type:
35           my $type = $snoop->guess_type("program.c");
36               # => "c"
37

DESCRIPTION

39       File::Comments guesses the type of a given file, determines the format
40       used for comments, extracts all comments, and returns them as a
41       reference to an array of chunks. Alternatively, it strips all comments
42       from a file.
43
44       Currently supported are Perl scripts, C/C++ programs, Java, makefiles,
45       JavaScript, Python and PHP.
46
47       The plugin architecture used by File::Comments makes it easy to add new
48       formats. To support a new format, a new plugin module has to be
49       installed.  No modifications to the File::Comments codebase are
50       necessary, new plugins will be picked up automatically.
51
52       File::Comments can also be used to simply guess a file's type. It it
53       somewhat more flexible than File::MMagic and File::Type.  File types in
54       File::Comments are typically based on file name suffixes (*.c, *.pl,
55       etc.). If no suffix is available, or a given suffix is ambiguous (e.g.
56       if several plugins have registered a handler for the same suffix), then
57       the file's content is used to narrow down the possibilities and arrive
58       at a decision.
59
60       WARNING: THIS MODULE IS UNDER DEVELOPMENT, QUALITY IS ALPHA. IF YOU
61       FIND BUGS, OR WANT TO CONTRIBUTE PLUGINS, PLEASE SEND THEM MY WAY.
62
63   FILE TYPES
64       Currently, the following plugins are included in the File::Comments
65       distribution:
66
67           ###############################################
68           # plugin                              type    #
69           ###############################################
70             File::Comments::Plugin::C          c            (o)
71             File::Comments::Plugin::Makefile   makefile  (X)
72             File::Comments::Plugin::Perl       perl      (X)
73             File::Comments::Plugin::JavaScript js           (o)
74             File::Comments::Plugin::Java       java         (o)
75             File::Comments::Plugin::HTML       html      (X)
76             File::Comments::Plugin::Python     python       (o)
77             File::Comments::Plugin::PHP        php          (o)
78
79                 (X) Fully implemented
80                 (o) Implemented with regular expressions, only works for
81                     easy cases until real parsers are employed.
82
83       The constants listed in the type column are the strings returned by the
84       "guess_type()" method.
85

Methods

87       $snoop = File::Comments->new()
88           Create a new comment extractor engine. This will automatically
89           initialize all plugins.
90
91           To avoid cold calls ("Cold Calls"), set "cold_calls" to a false
92           value (defaults to 1):
93
94               $snoop = File::Comments->new( cold_calls => 0 );
95
96           By default, if no plugin can be found for a given file,
97           "File::Comments" will throw a fatal error and "die()". If this is
98           undesirable and a default plugin should be used instead, it can be
99           specified in the constructor using the "default_plugin" parameter:
100
101               $snoop = File::Comments->new(
102                 default_plugin => "File::Comments::Plugin::Makefile"
103               );
104
105       $comments = $snoop->comments("program.c");
106           Extract all comments from a file. After determining the file type
107           by either suffix or content ("Cold Calls"), comments are extracted
108           as chunks and returned as a reference to an array.
109
110           To get a single string containing all comments, just join the
111           chunks:
112
113               my $comments_string = join '', @$comments;
114
115       $stripped_text = $snoop->stripped("program.c");
116           Strip all comments from a file. After determining the file type by
117           either suffix or content ("Cold Calls"), all comments are removed
118           and the stripped text is returned in a scalar.
119
120       $type = $snoop->guess_type("script.pl")
121           Guess the type of a file, based on either suffix, or in absense of
122           a suffix via "Cold Calls". Return the result as a string: "c",
123           "makefile", "perl", etc. ("FILE TYPES").
124
125       $snoop->suffix_registered("c")
126           Returns true if one of the plugins has registered the given suffix.
127
128   Writing new plugins
129       Writing a new plugin to add functionality to the File::Comments
130       framework is as simple as defining a new module, derived from the
131       baseclass of all plugins, "File::Comments::Plugin". Three additional
132       methods are needed: "init()", "type()", and "comments()".
133
134       "init()" gets called when the mothership finds the plugin and
135       initializes it. This is the time to register extensions that the plugin
136       wants to handle.
137
138       The second mandatory method for a plugin is "type()", which returns a
139       string, indicating the type of the file examined. Usually this can be
140       done without further ado, since a basic plugin will called only on
141       files which it registered for by suffix. Exceptions to this are
142       explained later.
143
144       The third method is "comments()", which returns a reference to an array
145       of comment lines. The content of the source file to be examined will be
146       available in
147
148           $self->{target}->{content}
149
150       by the time "comments()" gets called.
151
152       And that's it. Here's a functional basic plugin, registering a new
153       suffix ".odd" with the mothership and expecting files with comment
154       lines that start with "ODDCOMMENT":
155
156           ###########################################
157           package File::Comments::Plugin::Oddball;
158           ###########################################
159
160           use strict;
161           use warnings;
162           use File::Comments::Plugin;
163
164           our $VERSION = "0.01";
165           our @ISA     = qw(File::Comments::Plugin);
166
167           ###########################################
168           sub init {
169           ###########################################
170               my($self) = @_;
171
172               $self->register_suffix(".odd");
173           }
174
175           ###########################################
176           sub type {
177           ###########################################
178               my($self) = @_;
179
180               return "odd";
181           }
182
183           ###########################################
184           sub comments {
185           ###########################################
186               my($self) = @_;
187
188               # Some code to extract all comments from
189               # $self->{target}->{content}:
190               my @comments = ($self->{target}->{content} =~ /^ODDCOMMENT:(.*)/);
191               return \@comments;
192           }
193
194           1;
195
196   Cold Calls
197       If a file doesn't have an extension or an extensions that's served by
198       multiple plugins, File::Comments will go shop around and ask all
199       plugins if they want to handle the file. The mothership calls each
200       plugin's "applicable()" method, passing it an object of type
201       "File::Comments::Target", which contains the following fields:
202
203       When the plugin gets such a cold call (indicated by the third parameter
204       to "applicable()", it can either accept or deny the request. To arrive
205       at a decision, it can peek into the target object. The Perl plugin
206       illustrates this:
207
208           ###########################################
209           sub applicable {
210           ###########################################
211               my($self, $target, $cold_call) = @_;
212
213               return 1 unless $cold_call;
214
215               return 1 if $target->{content} =~ /^#!.*perl\b/;
216
217               return 0;
218           }
219
220       If a plugin does not define a "applicable()" method, a default method
221       is inherited from the base class "File::Comments::Plugin", which looks
222       like this:
223
224           ###########################################
225           sub applicable {
226           ###########################################
227               my($self, $target, $cold_call) = @_;
228
229               return 0 if $cold_call;
230               return 1;
231           }
232
233       This will deny all cold calls and only accept requests for files with
234       suffixes or base names the plugin has already signed up for.
235
236   Plugin Inheritance
237       Plugins can reuse existing plugins by inheritance. For example, if you
238       wanted to write a catch-all plugin that takes over all cold calls and
239       handles comments like the "Makefile" plugin, you can simply use
240
241           ###########################################
242           package File::Comments::Plugin::Catchall;
243           ###########################################
244
245           use strict;
246           use warnings;
247           use File::Comments::Plugin;
248           use File::Comments::Plugin::Makefile;
249
250           our $VERSION = "0.01";
251           our @ISA     = qw(File::Comments::Plugin::Makefile);
252
253           ###########################################
254           sub applicable {
255           ###########################################
256               my($self) = @_;
257
258               return 1;
259           }
260
261       "File::Comments::Plugin::Catchall" just implements "applicable()" and
262       inherits everything else from "File::Comments::Plugin::Makefile".
263

LEGALESE

265       Copyright 2005 by Mike Schilli, all rights reserved.  This program is
266       free software, you can redistribute it and/or modify it under the same
267       terms as Perl itself.
268

AUTHOR

270       2005, Mike Schilli <cpan@perlmeister.com>
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274perl v5.34.0                      2021-07-22                 File::Comments(3)
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