MooseX::App(3) Write user-friendly command line apps with even less suffering


In your base class:

package MyApp;
use MooseX::App qw(Color);

option 'global_option' => (
is => 'rw',
isa => 'Bool',
documentation => q[Enable this to do fancy stuff],
); # Global option

has 'private' => (
is => 'rw',
); # not exposed

Write multiple command classes (If you have only a single command class you should use MooseX::App::Simple instead)

  package MyApp::SomeCommand;
  use MooseX::App::Command; # important (also imports Moose)
  extends qw(MyApp); # optional, only if you want to use global options from base class
  # Positional parameter
  parameter 'some_parameter' => (
      is            => 'rw',
      isa           => 'Str',
      required      => 1,
      documentation => q[Some parameter that you need to supply],
  option 'some_option' => (
      is            => 'rw',
      isa           => 'Int',
      required      => 1,
      documentation => q[Very important option!],
  ); # Option
  sub run {
      my ($self) = @_;
      # Do something

And then you need a simple wrapper script (called eg. myapp):

 #!/usr/bin/env perl
 use MyApp;

On the command line:

 bash$ myapp help
     myapp <command> [long options...]
     myapp help
 global options:
     --global_option    Enable this to do fancy stuff [Flag]
     --help --usage -?  Prints this usage information. [Flag]
 available commands:
     some_command    Description of some command
     another_command Description of another command
     help            Prints this usage information


 bash$ myapp some_command --help
     myapp some_command <SOME_PARAMETER> [long options...]
     myapp help
     myapp some_command --help
     some_parameter     Some parameter that you need to supply [Required]
     --global_option    Enable this to do fancy stuff [Flag]
     --some_option      Very important option! [Int,Required]
     --help --usage -?  Prints this usage information. [Flag]


MooseX-App is a highly customisable helper to write user-friendly command line applications without having to worry about most of the annoying things usually involved. Just take any existing Moose class, add a single line ("use MooseX-App qw(PluginA PluginB ...);") and create one class for each command in an underlying namespace. Options and positional parameters can be defined as simple Moose accessors using the "option" and "parameter" keywords respectively.

MooseX-App will then

  • Find, load and initialise the command classes (see MooseX::App::Simple for single class/command applications)
  • Create automated help and documentation from modules POD as well as attributes metadata and type constraints
  • Read, encode and validate the command line options and positional parameters entered by the user from @ARGV and %ENV (and possibly prompt the user for additional parameters see MooseX::App::Plugin::Term)
  • Provide helpful error messages if user input cannot be validated (either missing or wrong attributes or Moose type constraints not satisfied)

Commandline options are defined using the 'option' keyword which accepts the same attributes as Moose' 'has' keyword.

  option 'some_option' => (
      is            => 'rw',
      isa           => 'Str',

This is equivalent to

  has 'some_option' => (
      is            => 'rw',
      isa           => 'Str',
      traits        => ['AppOption'],   # Load extra metaclass
      cmd_type      => 'option',        # Set attribute type

Single letter options are treated as flags and may be combined with eachother.

Positional parameters are defined with the 'parameter' keyword

  parameter 'some_option' => (
      is            => 'rw',
      isa           => 'Str',

This is equivalent to

  has 'some_option' => (
      is            => 'rw',
      isa           => 'Str',
      traits        => ['AppOption'],
      cmd_type      => 'parameter',

All keywords are imported by Moosex::App (in the app base class) and MooseX::App::Command (in the command class) or MooseX::App::Simple (single class application).

Furthermore, all options and parameters can also be supplied via %ENV

  option 'some_option' => (
      is            => 'rw',
      isa           => 'Str',
      cmd_env       => 'SOME_OPTION', # sets the env key

Moose type constraints help MooseX::App to construct helpful error messages and parse @ARGV in a meaningful way. The following type constraints are supported:

  • ArrayRef: Specify multiple values ('--opt value1 --opt value2', also see app_permute and cmd_split)
  • HashRef: Specify multiple key value pairs ('--opt key=value --opt key2=value2', also see app_permute)
  • Enum: Display all possibilities
  • Bool: Flags that do not require values
  • Int, Num: Used for proper error messages

Read the Tutorial for getting started with a simple MooseX::App command line application.



 my $myapp_command = MyApp->new_with_command();

This constructor reads the command line arguments and tries to create a command class instance. If it fails it returns a MooseX::App::Message::Envelope object holding an error message.

You can pass a hash of default/fallback params to new_with_command

 my $obj = MyApp->new_with_command(%default);

Optionally you can pass a custom ARGV to this constructor

 my $obj = MyApp->new_with_command( ARGV => \@myARGV );

However, if you do so you must take care of propper @ARGV encoding yourself.


 my $obj = MyApp->initialize_command_class($command_name,%default);

Helper method to instantiate the command class for the given command.


These options may be used to alter the default behaviour of MooseX-App.


 app_base 'my_script'; # Defaults to $0

Usually MooseX::App will take the name of the calling wrapper script to construct the program name in various help messages. This name can be changed via the app_base function.


 app_fuzzy 1; # default
 app_fuzzy 0;

Enables fuzzy matching of commands and attributes. Is turned on by default.


 app_strict 0; # default 
 app_strict 1;

If strict is enabled the program will terminate with an error message if superfluous/unknown positional parameters are supplied. If disabled all extra parameters will be copied to the extra_argv attribute.

The command_strict config in the command classes allows one to set this option individually for each command in the respective command class.


 app_prefer_commandline 0; # default
 app_prefer_commandline 1;

Specifies if parameters/options supplied via @ARGV,%ENV should take precedence over arguments passed directly to new_with_command.


 app_namespace 'MyApp::Commands', 'YourApp::MoreCommands';

Usually MooseX::App will take the package name of the base class as the namespace for commands. This namespace can be changed and you can add multiple extra namespaces.

If app_namespace is called with no arguments then autoloading of command classes will be disabled entirely.


 app_command_name {
     my ($package_short,$package_full) = @_;
     # munge package name;
     return $command_name;

This coderef can be used to control how autoloaded package names should be translated to command names. If this command returns nothing the respective command class will be skipped and not loaded.


    do      => 'MyApp::Commands::DoSomething',
    undo    => 'MyApp::Commands::UndoSomething';

This keyword can be used to register additional commands. Especially useful in conjunction with app_namespace and disabled autoloading.


 app_description qq[Description text];

Set the app description text. If not set this information will be taken from the Pod DESCRIPTION or OVERVIEW sections. (see command_description to set usage per command)


 app_usage qq[myapp --option ...];

Set a custom usage text. If not set this will be taken from the Pod SYNOPSIS or USAGE section. If both sections are not available, the usage information will be autogenerated. (see command_usage to set usage per command)


 app_permute 0; # default
 app_permute 1;

Allows one to specify multiple values with one key. So instead of writing "--list element1 --list element2 --list element3" one might write "--list element1 element2 element3" for ArrayRef elements. HashRef elements may be expressed as <--hash key=value key2=value2>.


All MooseX::App classes will have two extra attributes


Carries all parameters from @ARGV that were not consumed (only if app_strict is turned off, otherwise superfluous parameters will raise an exception).


Help flag that is set when help was requested.


Options and parameters accept extra attributes for customisation:
  • cmd_tags - Extra tags (as used by the help)
  • cmd_flag - Override option/parameter name
  • cmd_aliases - Additional option/parameter name aliases
  • cmd_split - Split values into ArrayRefs on this token
  • cmd_position - Specify option/parameter order in help
  • cmd_env - Read options/parameters from %ENV
  • cmd_count - Value of option equals to number of occurrences in @ARGV

Refer to MooseX::App::Meta::Role::Attribute::Option for detailed documentation.


MooseX::App will use your class metadata and POD to construct the commands and helpful error- or usage- messages. These bits of information are utilised and should be provided if possible:
  • Package names
  • required options for Moose attributes
  • documentation options for Moose attributes
  • Moose type constraints (Bool, ArrayRef, HashRef, Int, Num, and Enum)
  • Documentation set via app_description, app_usage, command_short_description, command_long_description and command_usage
  • Dzil ABSTRACT tag if no POD is available yet


The behaviour of MooseX-App can be customised with plugins. To load a plugin just pass a list of plugin names after the "use MooseX-App" statement. (Attention: order sometimes matters)

 use MooseX::App qw(PluginA PluginB);

Currently the following plugins are shipped with MooseX::App

  • MooseX::App::Plugin::BashCompletion

    Adds a command that generates a bash completion script for your application. See third party MooseX::App::Plugin::ZshCompletion for Z shell completion.

  • MooseX::App::Plugin::Color

    Colorful output for your MooseX::App applications.

  • MooseX::App::Plugin::Config

    Config files for MooseX::App applications.

  • MooseX::App::Plugin::ConfigHome

    Try to find config files in users home directory.

  • MooseX::App::Plugin::Term

    Prompt user for options and parameters that were not provided via options or params. Prompt offers basic editing capabilities and non-persistent history.

  • MooseX::App::Plugin::Typo

    Handle typos in command names and provide suggestions.

  • MooseX::App::Plugin::Version

    Adds a command to display the version and license of your application.

  • MooseX::App::Plugin::Man

    Display full manpage of application and commands.

  • MooseX::App::Plugin::MutexGroup

    Allow for mutally exclusive options.

  • MooseX::App::Plugin::Depends

    Adds dependent options.

Refer to Writing MooseX-App Plugins for documentation on how to create your own plugins.


Startup time may be an issue - escpecially if you load many plugins. If you do not require the functionality of plugins and ability for fine grained customisation (or Moose for that matter) then you should probably use MooX::Options or MooX::Cmd.

In some cases - especially when using non-standard class inheritance - you may end up with command classes lacking the help attribute. In this case you need to include the following line in your base class

 with qw(MooseX::App::Role::Common);

When manually registering command classes (eg. via app_command_register) in multiple base classes with different sets of plugins (why would you ever want to do that?), then meta attributes may lack some attribute metaclasses. In this case you need to load the missing attribute traits explicitly:

 option 'argument' => (
    depends => 'otherargument',
    trait   => ['MooseX::App::Plugin::Depends::Meta::Attribute'], # load trait


Please report any bugs or feature requests to "[email protected]", or through the web interface at <>. I will be notified, and then you'll automatically be notified of progress on your report as I make changes.


    Maroš Kollár
    maros [at]


Special thanks to all contributors.

In no particular order: Andrew Jones, George Hartzell, Steve Nolte, Michael G, Thomas Klausner, Yanick Champoux, Edward Baudrez, David Golden, J.R. Mash, Thilo Fester, Gregor Herrmann, Sergey Romanov, Sawyer X, Roman F., Hunter McMillen, Maik Hentsche, Alexander Stoddard

You are more than welcome to contribute to MooseX-App. Please have a look at the <> list of open wishlist issues for ideas.


MooseX::App is Copyright (c) 2012-16 Maroš Kollár.

This library is free software and may be distributed under the same terms as perl itself. The full text of the licence can be found in the LICENCE file included with this module.