1App::Cmd::Tutorial(3) User Contributed Perl DocumentationApp::Cmd::Tutorial(3)
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6 App::Cmd::Tutorial - getting started with App::Cmd
7
9 version 0.311
10
12 App::Cmd is a set of tools designed to make it simple to write
13 sophisticated command line programs. It handles commands with multiple
14 subcommands, generates usage text, validates options, and lets you
15 write your program as easy-to-test classes.
16 An App::Cmd-based application is made up of three main parts: the
18 script, the application class, and the command classes.
19 The script is the actual executable file run at the command line. It
21 can generally consist of just a few lines:
22 #!/usr/bin/perl
24 use YourApp;
25 YourApp->run;
26 All the work of argument parsing, validation, and dispatch is taken
28 care of by your application class. The application class can also be
29 pretty simple, and might look like this:
30 package YourApp;
32 use App::Cmd::Setup -app;
33 1;
34 When a new application instance is created, it loads all of the command
36 classes it can find, looking for modules under the Command namespace
37 under its own name. In the above snippet, for example, YourApp will
38 look for any module with a name starting with "YourApp::Command::".
39 We can set up a simple command class like this:
41 package YourApp::Command::initialize;
43 use YourApp -command;
44 1;
45 Now, a user can run this command, but he'll get an error:
47 $ yourcmd initialize
49 YourApp::Command::initialize does not implement mandatory method 'execute'
50 Oops! This dies because we haven't told the command class what it
52 should do when executed. This is easy, we just add some code:
53 sub execute {
55 my ($self, $opt, $args) = @_;
56 print "Everything has been initialized. (Not really.)\n";
58 }
59 Now it works:
61 $ yourcmd initialize
63 Everything has been initialized. (Not really.)
64 The arguments to the execute method are the parsed options from the
66 command line (that is, the switches) and the remaining arguments. With
67 a properly configured command class, the following invocation:
68 $ yourcmd reset -zB --new-seed xyzxy foo.db bar.db
70 might result in the following data:
72 $opt = {
74 zero => 1,
75 no_backup => 1,
76 new_seed => 'xyzzy',
77 };
78 $args = [ qw(foo.db bar.db) ];
80 Arguments are processed by Getopt::Long::Descriptive (GLD). To
82 customize its argument processing, a command class can implement a few
83 methods: "usage_desc" provides the usage format string; "opt_spec"
84 provides the option specification list; "validate_args" is run after
85 Getopt::Long::Descriptive, and is meant to validate the $args, which
86 GLD ignores.
87 The first two methods provide configuration passed to GLD's
89 "describe_options" routine. To improve our command class, we might add
90 the following code:
91 sub usage_desc { "yourcmd %o [dbfile ...]" }
93 sub opt_spec {
95 return (
96 [ "skip-refs|R", "skip reference checks during init", ],
97 [ "values|v=s@", "starting values", { default => [ 0, 1, 3 ] } ],
98 );
99 }
100 sub validate_args {
102 my ($self, $opt, $args) = @_;
103 # we need at least one argument beyond the options; die with that message
105 # and the complete "usage" text describing switches, etc
106 $self->usage_error("too few arguments") unless @$args;
107 }
108
110 · Delay using large modules using autouse, Class::Autouse or
111 "require" in your commands to save memory and make startup faster.
112 Since only one of these commands will be run anyway, there's no
113 need to preload the requirements for all of them.
114 · To add a "--help" option to all your commands create a base class
116 like:
117 package MyApp::Command;
119 use App::Cmd::Setup -command;
120 sub opt_spec {
122 my ( $class, $app ) = @_;
123 return (
124 [ 'help' => "This usage screen" ],
125 $class->options($app),
126 )
127 }
128 sub validate_args {
130 my ( $self, $opt, $args ) = @_;
131 die $self->_usage_text if $opt->{help};
132 $self->validate( $opt, $args );
133 }
134 Where "options" and "validate" are "inner" methods which your
136 command subclasses implement.
137 · To let your users configure default values for options, put a sub
139 like
140 sub config {
142 my $app = shift;
143 $app->{config} ||= TheLovelyConfigModule->load_config_file();
144 }
145 in your main app file, and then do something like:
147 sub opt_spec {
149 my ( $class, $app ) = @_;
150 my ( $name ) = $class->command_names;
151 return (
152 [ 'blort=s' => "That special option",
153 { default => $app->config->{$name}{blort} || $fallback_default },
154 ],
155 );
156 }
157 Or better yet, put this logic in a superclass and process the
159 return value from an "inner" method (see previous tip for an
160 example).
161
163 Ricardo Signes <rjbs@cpan.org>
164
166 This software is copyright (c) 2011 by Ricardo Signes.
167 This is free software; you can redistribute it and/or modify it under
169 the same terms as the Perl 5 programming language system itself.
170perl v5.12.3 2011-03-18 App::Cmd::Tutorial(3)