Tuesday, November 23, 2010

Intro to App::CLI

My first meet with App::CLI is in the summer of 2008, trying to write JiftyX::Fixtures. Without abundant PODs coming with this module, it took me almost one day to understand this module through trial and error. Since, I write this intro to reveal more power from this module; even I have contribute some code and DOCs to the project.

Actually, App::CLI is a really powerful module having central idea similar to the dispatcher in many web application frameworks such as Rails. When we are trying to create yet another handy CLI tool for our daily working, here is a recommended architecture to use App::CLI:

-> The kernel of our new tool

-> All other module forming the mechanism
-> of our new tool, e.g. MyApp::Config
-> for loading configuration

-> The dispatcher serving the invoking commands

-> All subcommands invoked by MyApp::Command

-> All subsubcommands invoked by specific subcommand

-> subsubsubcommands *god*

After deciding what command we need to implement, we only have two things should be done. The first is making MyApp::Command be able to dispatch. What we need to do is only add use base qw(App::CLI); into it.

Now, in MyApp.pm or our script, where we want to invoke command, we can just say
MyApp::Command would automatically use @ARGV to determine what (sub)command it should invoke and find its package to *require*. For example, if we type $ myapp list user --sort age in terminal, the @ARGV would be qw(list user --sort age), and MyApp::Command would require MyApp::Command::List::User, create its instance as $cmd, assign $cmd->{sort} as 'age', finally invoke $cmd->run_command().

So, The second thing, most of we need to effort, is to implement our (sub)commands. it's a bit like writing Controllers of Rails. If the URL matches /foo/bar/:id, the Action #list() of Controller Foo::Bar would handle the request, and @id would be assign value. If users type $ myapp list nickname --name /mark/ MyApp::Command::List::Nickname would handle the command and $instance->{name} would be assign string /mark/. For this case, we can write as below.

package MyApp::Command::List;
use base qw(App::CLI::Command);
use constant subcommands => qw(User Nickname);
use constant options => (
"h|help" => "help",

sub run {
my ($self, @args) = @_;
if ($self->{help}){
# output PODs when $ myapp list --help
# do something when user type like
# $ myapp list arg1 arg2 --opt1 --opt2 opt_arg2
# and arg1 doesn't equal to User or Nickname

package MyApp::Command::List::Nickname;
use base qw(App::CLI::Command);
use constant options => (
"name=s" => "name",

sub run {
my ($self, @args) = @_;
$name = $self->{name} #=> /mark/
# query the data base via condition /mark/

It completes. Note the we can specify all possible subcommands in constant subcommands of and give all possible options in constant options to all (sub)commands and just implement &run() the (sub)command would be done. And finally, note we can cascading subcommands infinitely. That is the core power of this module starting from v0.2.


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