NAME

CLI::Framework::Application - Build standardized, flexible, testable command-line applications

SYNOPSIS

#---- CLIF Application class -- lib/My/Journal.pm
package My::Journal;
use base qw( CLI::Framework::Application );

sub init {
    my ($self, $opts) = @_;
    # ...connect to DB, getting DB handle $dbh...
    $self->session('dbh' => $dbh); # (store $dbh in shared session slot)
}
1;

#---- CLIF Command class -- lib/My/Journal/Command/Entry.pm
package My::Journal::Command::Entry;
use base qw( CLI::Framework::Command );

sub run { ... }
1;

#---- CLIF (sub)Command Class -- can be defined inline in master command
# package file for My::Journal::Command::Entry or in dedicated package
# file lib/My/Journal/Command/Entry/Add.pm
package My::Journal::Command::Entry::Add;
use base qw( My::Journal::Command::Entry );

sub run { ... }
1;

#---- ...<more similar class definitions for 'entry' subcommands>...

#---- CLIF Command Class -- lib/My/Journal/Command/Publish.pm
package My::Journal::Command::Publish;
use base qw( CLI::Framework::Command );

sub run { ... }
1;

#---- CLIF executable script: journal
use My::Journal;
My::Journal->run();

#---- Command-line
$ journal entry add 'today I wrote some POD'
$ journal entry search --regex='perl'
$ journal entry print 1 2 3
$ journal publish --format=pdf --template=my-journal --out=~/notes/journal-20090314.txt

OVERVIEW

CLI::Framework (nickname "CLIF") provides a framework and conceptual pattern for building full-featured command line applications. It intends to make this process easy and consistent. It assumes responsibility for common details that are application-independent, making it possible for new CLI applications to be built without concern for these recurring aspects (which are otherwise very tedious to implement).

For instance, the Journal application example in the SYNOPSIS is an example of a CLIF application for a personal journal. The application has both commands and subcommands. Since the application class, My::Journal, is a subclass of CLI::Framework::Application, the Journal application is free to focus on implementation of its individual commands with minimum concern for the many details involved in building an interface around those commands. The application is composed of concise, understandable code in packages that are easy to test and maintain. This methodology for building CLI apps can be adopted as a standardized convention.

UNDERSTANDING CLIF: RECOMMENDATIONS

"Quickstart" and "Tutorial" guides are currently being prepared for the next CLIF release. However, this early version has the necessary content. See especially CLI::Framework::Application and CLI::Framework::Command. Also, there are example CLIF applications (demonstrating both simple and advanced usage) included with the tests for this distribution.

MOTIVATION

There are a few other distributions on CPAN intended to simplify building modular command line applications. None of them met my requirements, which are documented in DESIGN GOALS.

DESIGN GOALS/FEATURES

CLIF was designed to offer the following features...

• A clear conceptual pattern for creating CLI apps

• Guiding documentation and examples

• Convenience for simple cases, flexibility for complex cases

• Support for both non-interactive and interactive modes (without extra work)

• Separation of Concerns to decouple data model, control flow, and presentation

• The possibility to share some components with MVC web apps

• Commands that can be shared between apps (and uploaded to CPAN)

• Validation of app options

• Validation of per-command options and arguments

• A model that encourages easily-testable applications

• Flexible way to provide usage/help information for the application as a whole and for individual commands

• Support for subcommands that work just like commands

• Support for recursively-defined subcommands (sub-sub-...commands to any level of depth)

• Support aliases for commands and subcommands

• Allow subcommand package declarations to be defined inline in the same file as their parent command or in separate files per usual Perl package file hierarchy organization

• Support the concept of a default command for the application

CONCEPTS AND DEFINITIONS

• Application Script - The wrapper program that invokes the CLIF Application's run method.

• Valid Commands - The set of command names available to a running CLIF-derived application. This set contains the client-programmer-defined commands and all registered built-in commands.

• Metacommand - An application-aware command. Metacommands are subclasses of CLI::Framework::Command::Meta. They are identical to regular commands except they hold a reference to the application within which they are running. This means they are able to "know about" and affect the application. For example, the built-in command 'Menu' is a Metacommand because it needs to produce a list of the other commands in its application.

  In general, your commands should be designed to operate independently of the application, so they should simply inherit from CLI::Framework::Command. The Metacommand facility is useful but should only be used when necessary.

• Non-interactive Command - In interactive mode, some commands need to be disabled. For instance, the built-in 'console' command should not be presented as a menu option in interactive mode because it is already running. You can designate which commands are non-interactive by overriding the noninteractive_commands method.

• Options hash - A Perl hash that is created by the framework based on user input. The hash keys are option names (from among the valid options defined in an application's option_spec method) and the values are the scalars passed by the user via the command line.

• Command names - The official name of each CLIF command is defined by the value returned by its name method. Names are handled case-sensitively throughout CLIF.

• Registration of commands - The CLIF Commands within an application must be registered with the application. The names of commands registered within an application must be unique.

APPLICATION RUN SEQUENCE

When a command of the form:

$ app [app-opts] <cmd> [cmd-opts] { <cmd> [cmd-opts] {...} } [cmd-args]

...causes your application script, <app>, to invoke the run() > method in your application class, CLI::Framework::Application performs the following actions:

1. Parse the application options [app-opts], command name <cmd>, command options [cmd-opts], and the remaining part of the command line (which includes command arguments [cmd-args] for the last command and may include multiple subcommands; everything between the { ... } represents recursive subcommand processing).

   If the command request is not well-formed, it is replaced with the default command and any arguments present are ignored. Generally, the default command prints a help or usage message.

2. Validate application options.

3. Initialize application.

4. Invoke command pre-run hook.

5. Dispatch command.

These steps are explained in more detail below...

Validation of application options

Your application class can optionally define the validate_options method.

If your application class does not override this method, validation is effectively skipped -- any received options are considered to be valid.

Application initialization

Your application class can optionally override the init method. This is an optional hook that can be used to perform any application-wide initialization that needs to be done independent of individual commands. For example, your application may use the init method to connect to a database and store a connection handle which is needed by most of the commands in the application.

Command pre-run

Your application class can optionally have a pre_dispatch method that is called with one parameter: the Command object that is about to be dispatched. This hook is called in void context. Its purpose is to allow applications to do whatever may be necessary to prepare for running the command. For example, the pre_dispatch method could set a database handle in all command objects so that every command has access to the database. As another example, a log entry could be inserted as a record of the command being run.

Dispatching a command

CLIF uses the dispatch method to actually dispatch a specific command. That method is responsible for running the command or delegating responsibility to a subcommand, if applicable.

See dispatch for the specifics.

INTERACTIVITY

After building your CLIF-based application, in addition to basic non-interactive functionality, you will instantly benefit from the ability to (optionally) run your application in interactive mode. A readline-enabled application command console with an event loop, a command menu, and built-in debugging commands is provided by default.

BUILT-IN COMMANDS INCLUDED IN THIS DISTRIBUTION

This distribution comes with some default built-in commands, and more CLIF built-ins can be installed as they become available on CPAN.

Use of the built-ins is optional in most cases, but certain features require specific built-in commands (e.g. the Help command is a fundamental feature and the Menu command is required in interactive mode). You can override any of the built-ins.

The existing built-ins and their corresponding packages are as follows (for more information on each, see the respective documentation):

help

CLI::Framework::Comand::Help

NOTE: This command is registered automatically. It can be overridden, but a 'help' command is mandatory.

list

CLI::Framework::Comand::List

dump

CLI::Framework::Comand::Dump

tree

CLI::Framework::Comand::Tree

console

CLI::Framework::Comand::Console

menu

CLI::Framework::Comand::Menu

NOTE: This command may be overridden, but the overriding command class MUST inherit from this one, conforming to its interface.

METHODS: OBJECT CONSTRUCTION

new

My::Application->new( interactive => 1 );

Construct a new CLIF Application object.

METHODS: COMMAND INTROSPECTION & REGISTRATION

is_valid_command

$app->is_valid_command( 'foo' );

Returns a true value if the specified command name is valid within the running application. Returns a false value otherwise.

command_search_path

$path = $app->command_search_path();

This method returns the path that should be searched for command class package files. If not overridden, the directory will be named 'Command' and will be under a sibling directory of your application class package named after the application class (e.g. if your application class is lib/My/App.pm, the default command search path will be lib/My/App/Command/).

get_registered_command_names

@registered_commands = $app->get_registered_command_names();

Returns a list of the names of all registered commands.

get_registered_command

my $command_object = $app->get_registered_command( $command_name );

Given the name of a registered command, returns the corresponding CLI::Framework::Command object. If the command is not registered, returns undef.

register_command

# Register by name...
$command_object = $app->register_command( $command_name );
# ...or register by object reference...
$command_object = CLI::Framework::Command->new( ... );
$app->register_command( $command_object );

Register a command to be recognized by the application. This method accepts either the name of a command or a reference to a CLI::Framework::Command object.

If a CLI::Framework::Command object is given and it is one of the commands specified to be valid, the command is registered and returned.

For registration by command name, an attempt is made to find the command with the given name. Preference is given to user-defined commands over built-ins, allowing user-defined versions to override built-in commands of the same name. If a user-defined command cannot be created, an attempt is made to register a built-in command by the given name. If neither attempt succeeds, an exception is thrown.

NOTE that registration of a command with the same name as one that is already registered will cause the existing command to be replaced by the new one. The commands registered within an application must be unique.

METHODS: PARSING & RUNNING COMMANDS

get_default_command

my $default = $app->get_default_command();

Retrieve the name of the default command.

set_default_command

$app->set_default_command( 'fly' );

Given a command name, makes it the default command for the application.

get_current_command

$status = $app->run();
print 'The command named: ', $app->get_current_command(), ' has completed';

Returns the name of the current command (or the one that was most recently run).

set_current_command

$app->set_current_command( 'roll' );

Given a command name, forward execution to that command. This might be useful (for example) in an application's init() method to redirect to another command.

get_default_usage

$usage_msg = $app->get_default_usage();

Get the default usage message for the application. This message is used as a last resort when usage information is unavailable by other means. See usage|/usage.

set_default_usage

$app->set_default_usage( $usage_message );

Set the default usage message for the application. This message is used as a last resort when usage information is unavailable by other means. See usage|/usage.

usage

# Application usage...
print $app->usage();

# Command-specific usage...
print $app->usage( $command_name, @subcommand_chain );

Returns a usage message for the application or a specific command.

If a command name is given, returns a usage message string for that command. If no command name is given or if no usage message is defined for the specified command, returns a general usage message for the application.

Logically, here is how the usage message is produced:

• If a valid command name is given, attempt to get usage message from the command; if no usage message is defined for the command, use the application usage message instead.

• If the application object has defined usage_text, use its return value as the usage message.

• Finally, fall back to using the default usage message returned by get_default_usage.

session

# Get the entire session hash...
$app->session();

# Get the value of an item from the session...
$app->session( 'key' );

# Set the value of an item in the session...
$app->session( 'key' => $value );

CLIF Applications may have a need for global data shared between all components (individual CLIF Commands and the Application object itself). session provides a way for this data to be stored, retreived, and shared between components.

run

MyApp->run();
# ...or...
$app->run();

This method controls the request processing and dispatching of a single command. It takes its input from @ARGV (which may be populated by a script running non-interactively on the command line) and dispatches the indicated command, capturing its return value. The command's return value should represent the output produced by the command. It is a scalar that is passed to render for final display.

METHODS: INTERACTIVITY

is_interactive

if( $app->is_interactive() ) {
    print "running interactively";
}

Accessor for the interactivity state of the application.

set_interactivity_mode

$app->set_interactivity_mode(1);

Set the interactivity state of the application. One parameter is accepted: a true or false value for whether the application state should be interactive or non-interactive, respectively.

is_interactive_command

$help_command_is_interactive = $app->is_interactive_command( 'help' );

Determine if the command with the specified name is an interactive command (i.e. whether or not the command is enabled in interactive mode). Returns a true value if it is; returns a false value otherwise.

get_interactive_commands

my @interactive_commands = $app->get_interactive_commands();

Return a list of all commands that are to be shown in interactive mode ("interactive commands").

run_interactive

MyApp->run_interactive();
# ...or...
$app->run_interactive();

Wrap the run method to create an event processing loop to prompt for and run commands in sequence. It uses the built-in command menu (or a user-defined menu-command, if one exists) to display available command selections.

Within this loop, valid input is the same as in non-interactive mode except that application options are not accepted (any application options should be handled before the interactive command loop is entered -- see the initialize parameter below).

The following parameters are recognized:

initialize: cause any options that are present in @ARGV to be procesed. One example of how this may be used: allow run_interactive() to process/validate application options and to run init prior to entering the interactive event loop to recognize commands.

invalid_request_threshold: the number of unrecognized command requests the user can enter before the menu is re-displayed.

read_cmd

$app->read_cmd();

This method is responsible for retreiving a command request and placing the tokens composing the request into @ARGV. It is called in void context.

The default implementation uses Term::ReadLine to prompt the user and read a command request, supporting command history.

Subclasses are encouraged to override this method if a different means of accepting user input is needed. This makes it possible to read command selections without assuming that the console is being used for I/O.

render

$app->render( $output );

This method is responsible for presentation of the result from a command. The default implementation simply attempts to print the $output scalar, assuming that it is a string.

Subclasses are encouraged to override this method to provide more sophisticated behavior such as processing the <$output> scalar through a templating system, if desired.

is_quit_signal

until( $app->is_quit_signal( $string_read_from_user ) ) { ... }

Given a string, return a true value if it is a quit signal (indicating that the application should exit) and a false value otherwise. quit_signals is an application subclass hook that defines what strings signify that the interactive session should exit.

METHODS: SUBCLASS HOOKS

There are several hooks that allow CLIF applications to influence the command execution process. This makes customizing the critical aspects of an application as easy as overriding methods. Subclasses can (and must, in some cases, as noted) override the following methods:

init

Overriding this hook is optional. It is called as follows:

$app->init( $app_options );

$app_options is a hash of pre-validated application options received and parsed from the command line. The option hash has already been checked against the options defined to be accepted by the application in option_spec.

This method allows CLIF applications to perform any common global initialization tasks that are necessary regardless of which command is to be run. Some examples of this include connecting to a database and storing a connection handle in the shared session slot for use by individual commands, setting up a logging facility that can be used by each command, or initializing settings from a configuration file.

pre_dispatch

Overriding this hook is optional. It is called as follows:

$app->pre_dispatch( $command_object );

This method allows applications to perform actions after each command object has been prepared for dispatch but before the command dispatch actually takes place.

option_spec

Overriding this hook is optional. An example of its definition is as follows:

sub option_spec {
    (
        [ 'verbose|v'   => 'be verbose'         ],
        [ 'logfile=s'   => 'path to log file'   ],
    )
}

This method should return an option specification as expected by the Getopt::Long::Descriptive function describe_options. The option specification defines what options are allowed and recognized by the application.

validate_options

This hook is optional. It is provided so that applications can perform validation of received options. It is called as follows:

$app->validate_options( $app_options );

$app_options is an options hash for the application.

This method should throw an exception (e.g. with die()) if the options are invalid.

NOTE that Getop::Long::Descriptive, which is used internally for part of the options processing, will perform some validation of its own based on the option_spec. However, the validate_options hook allows additional flexibility (if needed) in validating application options.

command_alias

Overriding this hook is optioal. It allows aliases for commands to be specified. The aliases will be recognized in place of the actual command names. This is useful for setting up shortcuts to longer command names.

An example of its definition:

sub command_alias {
{
    h   => 'help',
    l   => 'list',
    ls  => 'list',
    sh  => 'console',
    c   => 'console',
}
}

valid_commands

Overriding this hook is optional. An example of its definition is as follows:

sub valid_commands { qw( console list my-custom-command ... ) }

The hook should return a list of the names of each command that is to be supported by the application. If not overridden by the application subclass, the application will be very generic and have only the default commands.

Command names must be the same as the values returned by the name method of the corresponding Command class.

noninteractive_commands

Overriding this hook is optional.

Certain commands do not make sense to run interactively (e.g. the "console" command, which starts interactive mode). This method should return a list of their names. These commands will be disabled during interactive mode. By default, all commands are interactive commands except for console and menu.

quit_signals

Overriding this hook is optional.

sub quit_signals { qw( q quit exit ) }

An application can specify exactly what input represents a request to end an interactive session. By default, the three strings above are used.

usage_text

To provide application usage information, this method may be defined. It should return a string containing a useful help message for the overall application.

CLIF ERROR HANDLING POLICY

CLIF aims to make things simple for CLIF-derived applications. OO Exceptions are used internally, but CLIF apps are free to handle errors using any desired strategy.

The main implication is that Application and Command class hooks such as CLI::Framework::Application::validate_options() and CLI::Framework::Command::validate() are expected to indicate success or failure by throwing exceptions. The exceptions can be plain calls to die() or can be Exception::Class objects.

DIAGNOSTICS

Details will be provided pending finalizing error handling policies

CONFIGURATION & ENVIRONMENT

For interactive usage, Term::ReadLine is used. Depending on which readline libraries are available on your system, your interactive experience will vary (for example, systems with GNU readline can benefit from a command history buffer).

DEPENDENCIES

Carp

Getopt::Long::Descriptive

Class::Inspector

File::Spec

Text::ParseWords (only for interactive use)

Term::ReadLine (only for interactive use)

CLI::Framework::Exceptions

CLI::Framework::Command

DEFECTS AND LIMITATIONS

The CLIF distribution (CLI::Framework::*) is a work in progress! The current release is already quite effective, but there are several aspects that I plan to improve.

The following areas are currently targeted for improvement:

• Interface -- Be aware that the interface may change. Most likely, the changes will be small.

• Session handling -- Session handling is currently implemented in a temporary manner. Better session support is forthcoming.

• Error handling -- Exception objects are being used successfully, but more thorough planning needs to be done to finalize error handling policies.

• Feature set -- Possible additional features being considered include: enhanced support for using templates to render output of commands (including output from error handlers); an optional constructor with an interface that will allow the application and its commands to be defined inline, making it possible to generate an application without creating separate files to inherit from the base framework classes; a "web console" that will make the interactive mode available over the web.

• Documentation -- "Quickstart" and "Tutorial" guides are being written.

I plan another release soon that will offer some or all of these improvements. Suggestions and comments are welcome.

ACKNOWLEDGEMENTS

Many thanks to my colleagues at Informatics Corporation of America who have assisted by providing ideas and bug reports, especially Allen May.

SEE ALSO

CLI::Framework::Command

LICENSE AND COPYRIGHT

Copyright (c) 2009 Karl Erisman (karl.erisman@icainformatics.com), Informatics Corporation of America. All rights reserved.

This is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See perlartistic.

AUTHOR

Karl Erisman (karl.erisman@icainformatics.com)

cpanm CLI::Framework::Command

perl -MCPAN -e shell
install CLI::Framework::Command