NAME
CLI::Framework::Command - CLIF Command superclass
SYNOPSIS
See CLI::Framework::Tutorial for examples.
DESCRIPTION
CLI::Framework::Command (command class for use with CLI::Framework::Application) is the base class for CLIF commands. All CLIF commands inherit from this class.
CONCEPTS
- Subcommands
-
Commands can have "subcommands," which are also objects of this class. Subcommands can, in turn, have their own subcommands, and this pattern may repeat indefinitely.
NOTE that in this documentation, the term "command" may be used to refer to both commands and subcommands.
- Registration of subcommands
-
Subcommands are "registered" with their parent commands. The parent commands can then forward subcommand responsibilities as appropriate.
- File-based commands vs. inline commands
-
Command classes (which inherit from CLI::Framework::Command) can be defined in their own package files or they may be declared inline in another package (e.g. a command package file could include the declaration of a subcommand package or command packages could be declared inline in the package file where the application is declared). As long as the classes have been loaded (making their way into the symbol table), CLIF can use the commands.
OBJECT CONSTRUCTION
manufacture( $command_package )
# (manufacture MyApp::Command::Go and any subcommand trees beneath it)
my $go = CLI::Framework::Command->manufacture( 'MyApp::Command::Go' );CLI::Framework::Command is an abstract factory; manufacture() is the factory method that constructs and returns an object of the specific command class that is requested.
After instantiating an object of the requested command package, manufacture() attempts to load subcommands in the following 2 steps:
Attempt to find package files representing subcommands. For every subcommand S, S is registered as a child of the parent command. Next, steps 1 and 2 repeat, this time being invoked on S (i.e. with S as the parent in an attempt to find subcommands of S).
Attempt to find and register preloaded subcommands defined inline. Only preloaded subcommands are considered for registration (i.e. package files are not considered in this step). For every subcommand S, any preloaded subcommands that inherit directly from S are found and step 2 repeats for those classes.
Note the following rules about command class definition:
If a (sub)command class is defined inline, its subcommand classes must be defined inline as well.
If a (sub)command class is file-based, each of its subcommand classes can be either file-based or inline. Furthermore, it is not necessary for all of these subcommand classes to be defined in the same way -- a mixture of file-based and inline styles can be used for the subcommands of a given command.
new()
$object = $cli_framework_command_subclass->new();Basic constructor.
SHARED CACHE DATA
CLIF commands may need to share data with other commands and with their associated application. These methods support those needs.
set_cache( $cache_object )
Set the internal cache object for this instance.
See cache.
cache()
Retreive the internal cache object for this instance.
See cache for an explanation of how to use this simple cache object.
COMMAND DISPATCHING
get_default_usage() / set_default_usage( $default_usage_text )
Get or set the default usage message for the command. This message is used by usage.
NOTE: get_default_usage() merely retrieves the usage data that has already been set. CLIF only sets the default usage message for a command when processing a run request for the command. Therefore, the default usage message for a command may be empty (if a run request for the command has not been given and you have not otherwise set the default usage message).
$cmd->set_default_usage( ... );
$usage_msg = $cmd->get_default_usage();usage( $subcommand_name, @subcommand_chain )
# Command usage...
print $cmd->usage();
# Subcommand usage (to any level of depth)...
print $cmd->usage( $subcommand_name, @subcommand_chain );Attempts to find and return a usage message for a command or subcommand.
If a subcommand is given, returns a usage message for that subcommand. If no subcommand is given or if the subcommand cannot produce a usage message, returns a general usage message for the command.
Logically, here is how the usage message is produced:
If registered subcommand(s) are given, attempt to get usage message from a subcommand (NOTE that a sequence of subcommands could be given, e.g.
$cmd-usage('task', 'list' 'completed')>, which would result in the usage message for final subcommand,'completed'). If no usage message is defined for the subcommand, the usage message for the command is used instead.If the command has implemented usage_text, its return value is used as the usage message.
Finally, if no usage message has been found, the default usage message produced by get_default_usage is returned.
dispatch( $cmd_opts, @args )
For the given command request, dispatch performs any applicable validation and initialization with respect to supplied options $cmd_opts and arguments @args.
@args may indicate the request for a subcommand:
{ <subcmd> [subcmd-opts] {...} } [subcmd-args]If a subcommand registered under the indicated command is requested, the subcommand is initialized and dispatch()ed with its options [subcmd-opts] and arguments. Otherwise, the command itself is run().
This means that a request for a subcommand will result in the run() method of only the deepest-nested subcommand (because dispatch() will keep forwarding to successive subcommands until the args no longer indicate that a subcommand is requested). Furthermore, the only command that can receive args is the final subcommand in the chain (but all commands in the chain can receive options). However, NOTE that each command in the chain can affect the execution process through its notify_of_subcommand_dispatch method.
COMMAND REGISTRATION
registered_subcommand_names()
@registered_subcommands = $cmd->registered_subcommand_names();Return a list of the currently-registered subcommands.
registered_subcommand_object( $subcommand_name )
$subcmd_obj = $cmd->get_registered_subcommand( 'lock' );Given the name of a registered subcommand, return a reference to the subcommand object. If the subcommand is not registered, returns undef.
register_subcommand()
$cmd->register_subcommand( $subcmd_obj );Register $subcmd_obj as a subcommand under master command $cmd.
If $subcmd_obj is not a CLI::Framework::Command, returns undef. Otherwise, returns $subcmd_obj.
package_is_registered( $package_name )
Return a true value if the named class is registered as a subcommand. Returns a false value otherwise.
COMMAND SUBCLASS HOOKS
Just as CLIF Applications have hooks that subclasses can use, CLIF Commands are able to influence the command dispatch process via several hooks. Except where noted, all hooks are optional -- subclasses may choose not to override them.
name()
$s = My::Command::Squeak->new();
$s->name(); # => 'squeak'name() takes no arguments and returns the name of the command. The default implementation of this method uses the normalized base name of the package as the command name, e.g. the command defined by the package My::Application::Command::Xyz would be named 'xyz'.
Subclasses may override this if a different naming scheme is desired.
option_spec()
This method should return an option specification as expected by the Getopt::Long::Descriptive function describe_options. The option specification is a list of ARRAY refs that defines recognized options, types, multiplicities, etc. and specifies textual strings that are used as descriptions of each option:
sub option_spec {
[ "verbose|v" => "be verbose" ],
[ "logfile=s" => "path to log file" ],
}Subclasses should override this method if commands accept options (otherwise, the command will not recognize any options).
subcommand_alias()
sub subcommand_alias {
rm => 'remove',
new => 'create',
j => 'jump',
r => 'run',
}Subcommands can have aliases to support shorthand versions of subcommand names.
Subclasses should override this method if subcommand aliases are desired. Otherwise, the subcommands will only be recognized by their full command names.
validate( $cmd_opts, @args )
To provide strict validation of a command request, a subclass may override this method. Otherwise, validation is skipped.
$cmd_opts is an options hash with the received command options as keys and their values as hash values.
@args is a list of the received command arguments.
validate() is called in void context. It is expected to throw an exception if validation fails. This allows your validation routine to provide a context-specific failure message.
NOTE that Getop::Long::Descriptive performs some validation of its own based on the option_spec. However, validate() allows more flexibility in validating command options and also allows validation of arguments.
notify_of_subcommand_dispatch( $subcommand, $cmd_opts, @args )
If a request for a subcommand is received, the master command itself does not run(). Instead, its notify_of_subcommand_dispatch() method is called. This gives the master command a chance to act before the subcommand is run.
For example (please pardon this contrived example), suppose your application, 'queue', has a command hierarchy with multiple commands:
enqueue
dequeue
print
property
constraint
maxlen
behavior
...In this case, queue property constraint maxlen might set the max length property for a queue. If the command hierarchy was built this way, maxlen would be the only command to run in response to that request. If constraint, the master command of maxlen, needs to hook into this execution path, notify_of_subcommand_dispatch() could be overridden in the command class that implements constraint. notify_of_subcommand_dispatch() would then be called just before dispatching maxlen.
The notify_of_subcommand_dispatch() method is called in void context.
$subcommand is the subcommand object.
$cmd_opts is the options hash for the subcommand.
@args is the argument list for the subcommand.
usage_text()
If implemented, this method should simply return a string containing usage information for the command. It is used automatically to provide context-specific help.
Implementing this method is optional. See usage for details on how usage information is generated within the context of a CLIF application.
run( $cmd_opts, @args )
This method is responsible for the main execution of a command. It is called with the following parameters:
$cmd_opts is a pre-validated options hash with command options as keys and their user-provided values as hash values.
@args is a list of the command arguments.
The default implementation of this method simply calls usage to show help information for the command. Therefore, subclasses will usually override run() (Occasionally, it is useful to have a command that does little or nothing on its own but has subcommands that define the real behavior. In such relatively uncommon cases, it may not be necessary to override run()).
If an error occurs during the execution of a command via its run() method, the run() method code should throw an exception. The exception will be caught and handled appropriately by CLIF.
The return value of run() is treated as data to be output by the render method in your CLIF Application class. Note that nothing should be printed directly in your implementation of run. If no output is to be produced, your run() method should return undef or empty string.
DIAGNOSTICS
Error: failed to instantiate command package <command pkg> via new()-
manufacture was asked to manufacture an object of class <command pkg>, but failed while trying to invoke its constructor.
Error: failed to instantiate subcommand '<class>' via method new()-
Object construction for the subcommand <class> (whose package has already been
require()d) was unsuccessful. cannot opendir <dir>-
While trying to manufacture subcommands in a directory tree, calling
opendir()on the subdirectory with the name of the parent command failed.
CONFIGURATION & ENVIRONMENT
No special configuration requirements.
DEPENDENCIES
Carp
SEE ALSO
LICENSE AND COPYRIGHT
Copyright (c) 2009 Karl Erisman (karl.erisman@icainformatics.com), ICA Informatics. 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)