App::Cmdline

- NAME
- VERSION
- SYNOPSIS
- DESCRIPTION
- METHODS
  - Summary of methods
  - opt_spec
  - composed_of
  - check_for_duplicates
  - getopt_conf
  - usage_desc
  - validate_args
  - execute
- PREDEFINED SETS OF OPTIONS
  - How to create a new predefined set
- AUTHOR
- COPYRIGHT AND LICENSE

# NAME

App::Cmdline - helper for writing command-line applications

# VERSION

version 0.1.2

# SYNOPSIS

In your command-line script, e.g. in myapp:

       use App::myapp;
       App::myapp->run;

Such command-line script will be executed, for example, by:

      senger@ShereKhan$ myapp --version
      senger@ShereKhan$ myapp --check
      senger@ShereKhan$ myapp -c

In your module that does the full job you are implementing, e.g. in App/myapp.pm:

       package App::myapp;
       use parent 'App::Cmdline';

       # Define your own options, and/or add some predefined sets.
       sub opt_spec {
           my $self = shift;
           return $self->check_for_duplicates (
               [ 'check|c' => "only check the configuration"  ],
               $self->composed_of (
                   'App::Cmdline::Options::Basic',
                   'App::Cmdline::Options::DB',
               )
           );
       }

       # The main job is implemented here
       use Data::Dumper;
       sub execute {
           my ($self, $opt, $args) = @_;

           print STDERR "Started...\n" unless $opt->quiet;
           print STDOUT 'Options ($opt):    ' . Dumper ($opt);
           print STDOUT 'Arguments ($args): ' . Dumper ($args);
           ...
       }

# DESCRIPTION

This module helps to write command-line applications, especially if they need to be fed by some command-line options and arguments. It extends the App::Cmd::Simple module by adding the ability to use several predefined sets of options that many real command-line applications use and need anyway. For example, in most applications you need a way how to print its version or how to provide a decent help text. Once (or if) you agree with the way how it is done here, you can spend much less time with the almost-always-repeating options.

Your module (representing the application you are writing) should inherit from this module and implement, at least, the method opt_spec (optionally) and the method execute (mandatory).

# METHODS

In order to use the ability of composing list of options from the existing sets of predefined options (which is, after all, the main raison d'être of this module) use the method composed_of. And to find out that various predefined sets of options do not step on each other toes, use the method check_for_duplicates.

When writing a subclass of App::Cmdline, there are only a few methods that you might want to overwrite (except for execute that you must overwrite). Below are those that may be of your interest, or those that are implemented here slightly differently from the App::Cmd::Simple.

### Summary of methods

Methods that you must overwrite

         execute()

Methods that you should overwrite

         opt_spec()

Methods that you may overwrite

         usage_desc()
         validate_args()
         usage_error()
         getopt_conf()
         ...

Methods that you just call

         composed_of()
         check_for_duplicates()
         usage_error()

## opt_spec

This method returns a list with option definitions, each element being an arrayref. This returned list is passed (starting as its second argument) to `describe_options` from Getopt::Long::Descriptive. You need to check the documentation on how to specify options, but mainly each element is a pair of option specification and the help text for this option. For example:

       sub opt_spec {
           my $self = shift;
           return
               [ 'latitude|y=s'  => "geographical latitude"  ],
               [ 'longitude|x=s' => "geographical longitude" ],
           ;
       }

The option specification (the first part of each pair) is how the option can appear on the command-line, in its short or long version, if it takes a value, how/if can be repeated, etc.

The option elements can be richer. Another useful piece of the option definition is its default value - see an example of it in "OPTIONS" in App::Cmdline::Options::DB.

The example above, however, does not add anything new to the App::Cmd::Simple. Specifying the options this way, you could (and probably should) inherit directly from the App::Cmd::Simple without using `App::Cmdline`. Therefore, let's have another example:

       sub opt_spec {
           my $self = shift;
           return
               [ 'latitude|y=s'  => "geographical latitude"  ],
               [ 'longitude|x=s' => "geographical longitude" ],
               $self->composed_of (
                   'App::Cmdline::Options::Basic',
                   'App::Cmdline::Options::DB',
               );
       }

In this example, your command-line application will recognize the same options (latitude and longitude) as before and, additionally, all options that were predefined in the role classes App::Cmdline::Options::Basic and App::Cmdline::Options::DB. See more about these classes in "PREDEFINED SETS OF OPTIONS";

If not overridden, it returns an empty list.

## composed_of

The core method of this module. You call it with a list of names of the classes that are able to give back a list of predefined options that you may instantly use. The classes are not only specifying their options but, for some options, they also do something. For example, the `-h` option (defined in App::Cmdline::Options::Basic) prints the usage and exits.

This distribution contains few such classes (see the "PREDEFINED SETS OF OPTIONS"). Later, they may be published other similar classes providing different sets of options.

The method returns a list of options definitions that is suitable for including in the returned values of the opt_spec method (as it was shown in the example above). The returned value should always be used only at the end, after your application specifies its own options (those that are not coming from any predefined set). This is because the last element of the returned list is a hashref containing configuration for the Getopt::Long - as described in the Getopt::Long::Descriptive. Therefore, if you need to call this method more than once or not at the end, perhaps because you wish to see the options in the help usage in a different order, you need to remove its last element before you add anything after that:

       sub opt_spec {
           my $self = shift;
           my @db_options = $self->composed_of ('App::Cmdline::Options::DB');
           pop @db_options;
           return
               @db_options,
               [ 'latitude|y=s'  => "geographical latitude"  ],
               [ 'longitude|x=s' => "geographical longitude" ],
               $self->composed_of (
                   'App::Cmdline::Options::Basic',
               );
       }

The last example looks a bit inconvenient. And you do not need to do it that way - because the `composed_of` method accepts also any arrayrefs, ignoring them and just passing them to its return value. That's why you really can call this method only once and not to be bothered with the hashref at the end. Here is an example how you can combine class names (predefined sets) with your own option specification and/or usage separators (the empty arrayrefs):

        return
            [ 'check|c' => "only check the configuration"  ],
            [],
            $self->composed_of (
                'App::Cmdline::Options::DB',
                [ 'show|s' => "show database access properties"  ],
                [],
                'App::Cmdline::Options::Basic',
            );

which - when called with the -h option - shows this nicely formatted usage:

        Usage: myapp [short or long options, not bundled]
            -c --check      only check the configuration

            --dbname        database name
            --dbhost        hostname hosting database
            --dbport        database port number
            --dbuser        user name to access database
            --dbpasswd      password to access database
            --dbsocket      UNIX socket accessing the database
            -s --show       show database access properties

            -h              display a short usage message
            -v --version    display a version

## check_for_duplicates

When you are composing options from more sets, it is worth to check whether, unintentionally, some options are not duplicated. It can be done by this method that gets the list of options definitions, checks it (warning if any duplicate was found, and returning the same list unchanged. It can, therefore, be used like this:

       sub opt_spec {
           my $self = shift;
           return $self->check_for_duplicates (
               [ 'latitude|y=s'  => "geographical latitude"  ],
               [ 'longitude|x=s' => "geographical longitude" ],
               $self->composed_of (
                   'App::Cmdline::Options::Basic',
                   'App::Cmdline::Options::DB',
               )
           );
       }

## getopt_conf

The machinery behind the scene is done by the Getopt::Long module. This module can be configured by a list of strings in order to achieve a different interpretation of the command-line options. Such as to treat them case-insensitively, or to allow them to be bundled together. For the recognized strings you need to read the "Configuring Getopt::Long" in Getopt::Long. Here is shown how and when to use them.

The `App::Cmdline` provides a default set of strings:

       sub getopt_conf {
           return [
              'no_bundling',
              'no_ignore_case',
              'auto_abbrev',
           ];
       }

If you need it differently, override the getopt_conf method, returning an arrayref with configuration strings you want. Here are the examples showing the difference. Using the default configuration and having the following options:

       sub opt_spec {
           my $self = shift;
           return
               [ 'xpoint|x' => 'make an X point'],
               [ 'ypoint|y' => 'make a  Y point'],
               [],
               $self->composed_of (
                   'App::Cmdline::Options::Basic',
               );
       }

I can run (and get dumped the recognized options and arguments in the `execute` method:

       senger@ShereKhan2:myapp -x -y
       Executing...
       Options ($opt):    $VAR1 = bless( {
          'xpoint' => 1,
          'ypoint' => 1
           }, 'Getopt::Long::Descriptive::Opts::__OPT__::2' );
       Arguments ($args): $VAR1 = [];

You can see that both options, `-x` and `-y`, were recognized. But if I bundle them (and by default, the bundling is disabled), I get no recognized options; instead they will be shown as arguments (arguments being everything what remained not recognized on the command-line):

       senger@ShereKhan2:myapp -x -y
       Executing...
       Options ($opt):    $VAR1 = bless( {}, 'Getopt::Long::Descriptive::Opts::__OPT__::2' );
       Arguments ($args): $VAR1 = [ '-xy' ];

But if I change the configuration by implementing:

       sub getopt_conf {
           return [ 'bundling' ];
       }

the bundled options are now recognized as options (and no argument reminded):

       senger@ShereKhan2:myapp -xy
       Executing...
       Options ($opt):    $VAR1 = bless( {
          'xpoint' => 1,
          'ypoint' => 1
           }, 'Getopt::Long::Descriptive::Opts::__OPT__::2' );
       Arguments ($args): $VAR1 = [];

## usage_desc

The returned value from this method will be used as the first line of the usage message. The full usage is returned by another method, `usage`, that you usually do not overwrite because its default behaviour is to create a reasonable summary from the help texts you provided in the opt_spec method and, possibly, by this `usage_desc` method.

Behind the scene, the returned string is interpreted by the Getopt::Long::Descriptive which accepts also few special constructs:

- %c will be replaced with what `Getopt::Long::Descriptive` thinks is the program name (it is computed from $0).
- %o will be replaced with a list of the short options, as well as the text "[long options...]" if any have been defined.
- Literal % characters will need to be written as %%, just like with sprintf.

By default, the `App::Cmdline` returns slightly different usage description depending on the bundling configuration option (see getopt_conf): if the bundling is disabled, the bundle of all short options is not shown. Often, you want to use whatever `App::Cmdline` returns plus what you wish to add on the first line of the usage. For example:

       sub usage_desc {
           return shift->SUPER::usage_desc() . ' ...and anything else';
       }

## validate_args

Originally, this method was meant to check (validate) the command-line arguments (remember that arguments are whatever remains on the command-line after options defined in the opt_spec method have been processed). The options themselves could be already validated by various subroutines and attributes given in the option specifications (as described, sometimes only vaguely, in the Getopt::Long::Descriptive). But sometimes, it is useful to have all validation, of options and of arguments, in one place - so we have this method.

The method gets two parameters, `$opt` and `$args`. The first one is an instance of Getopt::Long::Descriptive::Opts giving you access to all existing options, using their names (as were defined in opt_spec) as the access methods. The second parameter is an arrayref containing all remaining arguments on the command-line.

Important: Some predefined sets of options (see the "PREDEFINED SETS OF OPTIONS") do also some checking (or other actions, like printing the version and exiting) and this checking is invoked from the `App::Cmdline`'s validate_args method. Therefore, it is strongly recommended that if you overwrite this method, you also call the SUPER:

       sub validate_args {
           my ($self, $opt, $args) = @_;
           $self->SUPER::validate_args ($opt, $args);
           if ($opt->number and scalar @$args != $opt->number) {
              $self->usage_error ("Option --number does not correspond with the number of arguments");
           }
       }

       senger@ShereKhan2:myapp -n 2 a b c
       Error: Option --number does not correspond with the number of arguments
       Usage: myapp [short or long options, not bundled] <some arguments...>
            -n --number     expected number of args
            -h              display a short usage message
            -v --version    display a version

The example also shows calling the method `usage_error`. Unless you overwrite also this method, it prints the given error message together with the usage and dies.

## execute

Last but definitely not least. You have to implement this method and put here whatever your command-line application is supposed to do.

The method gets two parameters, `$opt` and `$args`. The first one is an instance of Getopt::Long::Descriptive::Opts giving you access to all existing options, using their names (as were defined in opt_spec) as the access methods. The second parameter is an arrayref containing all remaining arguments on the command-line.

       sub execute {
           my ($self, $opt, $args) = @_;
           if ($opt->crystal eq 'ball') {
              print ask_ball ($args->[0]);
           } else {
              die "All is vanity...\n"
                 unless $opt->godess;
           }
       }

# PREDEFINED SETS OF OPTIONS

The predefined sets of options are represented by classes that are considered rather `roles`. You do not extend them (inherit from them) but you just use them (by naming them in the method composed_of).

This distribution bundles several of such classes. See their own documentation to find out what options they provide. Here is just a quick summary:

App::Cmdline::Options::Basic

  Provides basic options (help and version).

App::Cmdline::Options::ExtBasic

  Provides the same options as in App::Cmdline::Options::Basic and adds options for richer documentation.

App::Cmdline::Options::DB

  Provides options for accessing a database (user authentication, host and port name, etc.).

App::Cmdline::Options::ExtDB

  Provides the same options as in App::Cmdline::Options::DB and adds an option for showing what values were given by the database-related options.

### How to create a new predefined set

You may wish to create a new set of options if you want to re-use them. For application-specific options, used only once, you do not need to have a predefined set, you just specify them directly in the opt_spec method.

The classes that can be used as the predefined sets of options do not inherit from any common class (so far, there was no need for it) - unless one extends another one (as is the case of App::Cmdline::Options::ExtBasic). It is, however, recommended, to use the namespace App::Cmdline::Options:: - just to find them easier on CPAN.

Each of these classes should implement up to two methods:

get_opt_spec

  Strictly speaking, it is not mandatory, but without this method the class can hardly predefine any new options. The method should return a list of arrayrefs, suitable to be consumed by the opt_spec method. For example (taken from the App::Cmdline::Options::Basic):

         sub get_opt_spec {
             return
                 [ 'h'         => "display a short usage message"  ],
                 [ 'version|v' => "display a version"              ];
         }

validate_opts

  This method, if exists, will be called from the validate_args method. Its purpose is to do something with the options belonging to (predefined by) this class.

  It gets four parameters, `$app` (the class name of your application), `$caller` (who is calling), `$opts` (an object allowing to access all options) and `$args` (an arrayref with the remaining arguments from the command-line).

  If it finds an error, it usually dies by calling $caller->`usage_error`.

# AUTHOR

Martin Senger <martin.senger@gmail.com>

# COPYRIGHT AND LICENSE

This software is copyright (c) 2013 by Martin Senger, CBRC - KAUST (Computational Biology Research Center - King Abdullah University of Science and Technology) All Rights Reserved.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.