oracular (3) CLI::Framework.3pm.gz
NAME
CLI::Framework - Build standardized, flexible, testable command-line applications
OVERVIEW
CLI::Framework ("CLIF") provides a framework and conceptual pattern for building full-featured command
line applications. It intends to make this process simple and consistent. It assumes the responsibility
of implementing details that are common to all command-line applications, making it possible for new
applications adhering to well-defined conventions to be built without the need to repeatedly write the
same command-line interface code.
For instance, a complete application supporting commands and subcommands, with options and arguments for
the application itself as well as its commands, can be built by writing concise, understandable code in
packages that are easy to test and maintain. The classes can focus on implementation of unique aspects
essential to the command's purpose without being concerned with the many details involved in building an
interface around those commands. This methodology for building command-line applications also
establishes a valuable standard for an organization (or an individual developer).
LEARNING CLIF: RECOMMENDATIONS
CLIF has a rich set of features and offers many alternative approaches to building applications, but if
you are new to using it, you may want a succinct introduction. For this reason, the
CLI::Framework::Tutorial is provided and is the recommended starting point.
After you gain a basic understanding, the other documents can be used as references.
MOTIVATION
There are a few other distributions on CPAN intended to simplify building modular command line
applications. I have not found any that meet my requirements, which are documented in DESIGN GOALS AND
FEATURES.
DESIGN GOALS AND FEATURES
CLIF was designed to offer the following features...
• A clear conceptual pattern for creating command-line applications
• Guiding documentation and examples
• Convenience for simple cases, flexibility for complex cases
• Support for both non-interactive and interactive modes (with almost no additional work -- define the
necessary hooks and both modes will be supported)
• A design that naturally encourages MVC applications: decouple data model, control flow, and
presentation
• Commands that can be shared between applications (and uploaded to CPAN)
• The possibility to share some components with MVC web applications
• Validation of application options
• Validation of command options and arguments
• A model that encourages easily-testable applications
• A flexible means to provide usage/help information for the application as a whole and for individual
commands
• Support for subcommands that can be added as a natural extension to commands
• Support for recursively-defined subcommands (sub-sub-...commands to any level of depth)
• Support for aliases to commands and subcommands
• Allow Application and [sub]commands to be defined inline (some or all packages involved may be
defined in the same file) or split across multiple files
• Support the concept of a default command for the application
• Exception handling that allows individual applications to define custom exception handlers
• Performance. Core framework code should load as quickly as a simple script; individual commands
should be initialized only when invoked.
CONCEPTS AND DEFINITIONS
• Application Script - The wrapper program that invokes the CLIF Application's run method. The file it
is defined in may or may not also contain the definition of Application or Command packages.
• 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. This encourages looser coupling. However, in
exceptional cases, the use of Metacommands is warranted (For an example, see the built-in "Menu"
command).
• Non-interactive Command - In interactive mode, some commands need to be disabled. For instance, the
built-in "console" command (which is used to start interactive mode, presenting a command menu and
responding to user selections) 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.
• Registration of commands - Each CLIF application defines the commands it will support. These may be
built-in CLIF commands or custom CLIF commands. These commands are lazily "registered" as they are
called upon for use.
APPLICATION RUN SEQUENCE
When a command of the form:
$ app [app-opts] <cmd> [cmd-opts] { <cmd> [cmd-opts] {...} } [cmd-args]
examples:
app | [app-opts] { <cmd> | [cmd-opts] } [cmd-args]
`````````````````|```````````````````````````````````|`````````````|`````````````````|``````````````
$ examples/queue |--qin=/tmp/qfile --qout=/tmp/qfile | enqueue | --tag=x --tag=y | 'item'
`````````````````|```````````````````````````````````|`````````````|`````````````````|``````````````
$ gen-report | --html | stats | --role=admin |
| | usage | --time='2d' | '/tmp/stats.html'
````````````````````````````````````````````````````````````````````````````````````````````````````
...causes your application script, <app>, to invoke the run method in your application class,
CLI::Framework::Application performs the following actions:
1. Parse the command request
2. Validate application options
3. Initialize application
4. Prepare command
5. Invoke command pre-dispatch hook
6. Dispatch command
These steps are explained in more detail below...
Request parsing
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 inner brackets ("{ ... }") represents
recursive subcommand processing -- the ""..."" represents another string of ""<cmd> [cmd-opts] {...}"".
The second example above shows a command request that requires recursive subcommand processing. The
command might cause an HTML report to be generated with usage statistics for admin users (of some
application) for the past two days, writing the report to a file. In one line, it would look like this:
$ gen-report --html stats --role=admin usage --time='2d' '/tmp/stats.html'
This fictional gen-report application could be designed with such an interface because it could offer
various types of reports (as opposed to the statistics report). There might be other statistics reports
(as opposed to 'usage'). The stats might be available for users with other roles. The usage report
might need to accept custom time frames.
CLIF allows you to choose whether various parts of your data should be supplied as options or as
arguments -- these interface decisions are left to your discretion. CLIF also makes it easy to validate
command requests and to provide usage information so users know what to change if a command request fails
validation.
In general, if a command request is not well-formed, it is replaced with the default command and any
arguments present are ignored. The default command prints a help or usage message (you may change this
behavior if desired).
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 skipped -- any received options
are considered to be valid.
Application initialization
Your application class can optionally override the init method. This is a 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 may be needed by some or all of the commands in your application.
Preparing the command
The requested command is now loaded (if not already done). The command's cache is set (using a reference
to the same cache object used by the application).
Command pre-dispatch
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.
Dispatching the 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.
INTERACTIVITY
After building your CLIF 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.
Inside interactive mode, only steps 4, 5, and 6 above (APPLICATION RUN SEQUENCE) are performed for each
command request.
Supporting interactivity in your application is as simple as adding the built-in command
CLI::Framework::Command::Console to your command_map.
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 of all applications and the Menu command is required in
interactive mode). You can override any of the built-ins.
A new application that does not override the command_map hook will include all of the built-ins listed
below.
The existing built-ins and their corresponding packages are as follows:
help: Print application or command-specific usage messages
CLI::Framework::Command::Help
Note: This command is registered automatically. All CLIF applications must have the "help" command
defined (though this built-in can replaced by your subclass to change the "help" command behavior or
to do nothing if you specifically do not want a help command).
list: Print a list of commands available to the running application
CLI::Framework::Command::List
dump: Show the internal state of a running application
CLI::Framework::Command::Dump
tree: Display a tree representation of the commands that are currently registered with the running
application
CLI::Framework::Command::Tree
alias: Display the command aliases that are in effect for the running application and its commands
CLI::Framework::Command::Alias
console: Invoke CLIF's interactive mode
CLI::Framework::Command::Console
menu: Show a command menu including the commands that are available to the running application
CLI::Framework::Command::Menu
Note: This command is registered automatically when an application runs in interactive mode. This
built-in may be replaced by a user-defined "menu" command, but any command class to be used for the
"menu" command MUST be a subclass of this one.
CLIF ARCHITECTURE AT A GLANCE
The class diagram below shows the relationships of the major classes of CLI Framework, including some of
their methods. This is not intended to be a comprehensive diagram, only an aid to understanding CLIF at
a glance.
SEE ALSO
CLI::Framework::Application
CLI::Framework::Command
CLI::Framework::Tutorial
LICENSE AND COPYRIGHT
Copyright (c) 2009 Karl Erisman (kerisman@cpan.org). 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 (kerisman@cpan.org)