NAME¶
App::Cmd::Tutorial - getting started with App::Cmd
VERSION¶
version 0.324
DESCRIPTION¶
App::Cmd is a set of tools designed to make it simple to write sophisticated
command line programs. It handles commands with multiple subcommands,
generates usage text, validates options, and lets you write your program as
easy-to-test classes.
An App::Cmd-based application is made up of three main parts: the script, the
application class, and the command classes.
The Script¶
The script is the actual executable file run at the command line. It can
generally consist of just a few lines:
#!/usr/bin/perl
use YourApp;
YourApp->run;
The Application Class¶
All the work of argument parsing, validation, and dispatch is taken care of by
your application class. The application class can also be pretty simple, and
might look like this:
package YourApp;
use App::Cmd::Setup -app;
1;
When a new application instance is created, it loads all of the command classes
it can find, looking for modules under the Command namespace under its own
name. In the above snippet, for example, YourApp will look for any module with
a name starting with "YourApp::Command::".
The Command Classes¶
We can set up a simple command class like this:
# ABSTRACT: set up YourApp
package YourApp::Command::initialize;
use YourApp -command;
1;
Now, a user can run this command, but he'll get an error:
$ yourcmd initialize
YourApp::Command::initialize does not implement mandatory method 'execute'
Oops! This dies because we haven't told the command class what it should do when
executed. This is easy, we just add some code:
sub execute {
my ($self, $opt, $args) = @_;
print "Everything has been initialized. (Not really.)\n";
}
Now it works:
$ yourcmd initialize
Everything has been initialized. (Not really.)
Default Commands¶
By default applications made with App::Cmd know two commands:
"commands" and "help".
- commands
- lists available commands.
$yourcmd commands
Available commands:
commands: list the application's commands
help: display a command's help screen
init: set up YourApp
Note that by default the commands receive a description from the "#
ABSTRACT" comment in the respective command's module, or from the
"=head1 NAME" Pod section.
- help
- allows one to query for details on command's specifics.
$yourcmd help initialize
yourcmd initialize [-z] [long options...]
-z --zero ignore zeros
Of course, it's possible to disable or change the default commands, see
App::Cmd.
Arguments and Options¶
In this example
$ yourcmd reset -zB --new-seed xyzxy foo.db bar.db
"-zB" and "--new-seed xyzxy" are "options" and
"foo.db" and "bar.db" are "arguments."
With a properly configured command class, the above invocation results in nicely
formatted data:
$opt = {
zero => 1,
no_backup => 1, #default value
new_seed => 'xyzzy',
};
$args = [ qw(foo.db bar.db) ];
Arguments are processed by Getopt::Long::Descriptive (GLD). To customize its
argument processing, a command class can implement a few methods:
"usage_desc" provides the usage format string; "opt_spec"
provides the option specification list; "validate_args" is run after
Getopt::Long::Descriptive, and is meant to validate the $args, which GLD
ignores. See Getopt::Long for format specifications.
The first two methods provide configuration passed to GLD's
"describe_options" routine. To improve our command class, we might
add the following code:
sub usage_desc { "yourcmd %o [dbfile ...]" }
sub opt_spec {
return (
[ "skip-refs|R", "skip reference checks during init", ],
[ "values|v=s@", "starting values", { default => [ 0, 1, 3 ] } ],
);
}
sub validate_args {
my ($self, $opt, $args) = @_;
# we need at least one argument beyond the options; die with that message
# and the complete "usage" text describing switches, etc
$self->usage_error("too few arguments") unless @$args;
}
Global Options¶
There are several ways of making options available everywhere (globally). This
recipe makes local options accessible in all commands.
To add a "--help" option to all your commands create a base class
like:
package MyApp::Command;
use App::Cmd::Setup -command;
sub opt_spec {
my ( $class, $app ) = @_;
return (
[ 'help' => "this usage screen" ],
$class->options($app),
)
}
sub validate_args {
my ( $self, $opt, $args ) = @_;
if ( $opt->{help} ) {
my ($command) = $self->command_names;
$self->app->execute_command(
$self->app->prepare_command("help", $command)
);
exit;
}
$self->validate( $opt, $args );
}
Where "options" and "validate" are "inner" methods
which your command subclasses implement to provide command-specific options
and validation.
Note: this is a new file, previously not mentioned in this tutorial and this tip
does not recommend the use of global_opt_spec which offers an alternative way
of specifying global options.
TIPS¶
- •
- Delay using large modules using autouse, Class::Autouse or
"require" in your commands to save memory and make startup
faster. Since only one of these commands will be run anyway, there's no
need to preload the requirements for all of them.
- •
- Add a "description" method to your commands for more verbose
output from the built-in help command.
sub description {
return "The initialize command prepares ...";
}
- •
- To let your users configure default values for options, put a sub like
sub config {
my $app = shift;
$app->{config} ||= TheLovelyConfigModule->load_config_file();
}
in your main app file, and then do something like:
package YourApp;
sub opt_spec {
my ( $class, $app ) = @_;
my ( $name ) = $class->command_names;
return (
[ 'blort=s' => "That special option",
{ default => $app->config->{$name}{blort} || $fallback_default },
],
);
}
Or better yet, put this logic in a superclass and process the return value
from an "inner" method:
package YourApp::Command;
sub opt_spec {
my ( $class, $app ) = @_;
return (
[ 'help' => "this usage screen" ],
$class->options($app),
)
}
- •
- You need to activate "strict" and "warnings" as usual
if you want them. App::Cmd doesn't do that for you.
IGNORING THINGS¶
Some people find that for whatever reason, they wish to put Modules in their
"MyApp::Command::" namespace which are not commands, or not commands
intended for use by "MyApp".
Good examples include, but are not limited to, things like
"MyApp::Command::frobrinate::Plugin::Quietly", where
"::Quietly" is only useful for the "frobrinate" command.
The default behaviour is to treat such packages as errors, as for the majority
of use cases, things in "::Command" are expected to
only be
commands, and thus, anything that, by our heuristics, is not a command, is
highly likely to be a mistake.
And as all commands are loaded simultaneously, an error in any one of these
commands will yield a fatal error.
There are a few ways to specify that you are sure you want to do this, with
varying ranges of scope and complexity.
Ignoring a Single Module.¶
This is the simplest approach, and most useful for one-offs.
package YourApp::Command::foo::NotACommand;
use YourApp -ignore;
<whatever you want here>
This will register this package's namespace with YourApp to be excluded from its
plugin validation magic. It otherwise makes no changes to
"::NotACommand"'s namespace, does nothing magical with @ISA, and
doesn't bolt any hidden functions on.
Its also probably good to notice that it is ignored
only by
"YourApp". If for whatever reason you have two different
"App::Cmd" systems under which "::NotACommand" is visible,
you'll need to set it ignored to both.
This is probably a big big warning
NOT to do that.
Ignoring Multiple modules from the App level.¶
If you really fancy it, you can override the "should_ignore" method
provided by "App::Cmd" to tweak its ignore logic. The most useful
example of this is as follows:
sub should_ignore {
my ( $self, $command_class ) = @_;
return 1 if not $command_class->isa( 'App::Cmd::Command' );
return;
}
This will prematurely mark for ignoring all packages that don't subclass
"App::Cmd::Command", which causes non-commands ( or perhaps commands
that are coded wrongly / broken ) to be silently skipped.
Note that by overriding this method, you will lose the effect of any of the
other ignore mechanisms completely. If you want to combine the original
"should_ignore" method with your own logic, you'll want to steal
"Moose"'s "around" method modifier.
use Moose::Util;
Moose::Util::add_method_modifier( __PACKAGE__, 'around', [
should_ignore => sub {
my $orig = shift;
my $self = shift;
return 1 if not $command_class->isa( 'App::Cmd::Command' );
return $self->$orig( @_ );
}]);
SEE ALSO¶
CPAN modules using App::Cmd
<
http://deps.cpantesters.org/depended-on-by.pl?module=App%3A%3ACmd>
AUTHOR¶
Ricardo Signes <rjbs@cpan.org>
COPYRIGHT AND LICENSE¶
This software is copyright (c) 2014 by Ricardo Signes.
This is free software; you can redistribute it and/or modify it under the same
terms as the Perl 5 programming language system itself.