CLASP.Ruby

Command-Line Argument Sorting and Parsing, for Ruby

• Introduction
  • libCLImate.Ruby
• Installation
• Components
  • Command-line parsing
  • Declarative specification of the flags and options for a CLI
  • Utility functions for displaying usage and version information
• Examples
• Project Information
  • Where to get help
  • Contribution guidelines
  • Related projects
  • License

CLASP stands for Command-Line Argument Sorting and Parsing. The first CLASP library was a C library with a C++ wrapper (see project CLASP). There have been several implementations in other languages (as listed in Relation projects). CLASP.Ruby is the Ruby version.

All CLASP libraries provide the facilities to Command Line Interface (CLI) programs as described in detail below.

The libCLImate.Ruby library is implemented in terms of CLASP.Ruby but provides a higher-level abstration as well as several utility functions and the facility to fully specify command-line arguments declaratively in the __END__ section of a source file. More information and examples provided in the libCLImate.Ruby project.

Install via gem as in:

    gem install clasp-ruby

or add it to your Gemfile.

Use via require, as in:

require 'clasp'

All CLASP libraries discriminate between three types of command-line arguments:

• flags are hyphen-prefixed arguments that are either present or absent, and hence have a boolean nature;
• options are hyphen-prefixed arguments that are given values; and
• values are non-hyphen-prefixed arguments that represent values.

For example, in the command line

    myprog --all -c --opt1=val1 infile outfile

there are:

• two flags, --all and -c;
• one option called --opt1, which has the value val1; and
• two values infile and outfile.

Flags and options may have alias. If the alias for --all is -a and the alias for --opt1 is -o then the following command-line is exactly equivalent to the previous one:

    myprog -a -c -o val1 infile outfile

One-letter flags may be combined. Hence, the following command-line is exactly equivalent to the previous ones:

    myprog -ac -o val1 infile outfile

Option aliases may specify a value. If the alias -v1 means --opt1=val1 then the following command-line is exactly equivalent to the previous ones:

    myprog -ac -v1 infile outfile

Option aliases that are one letter may be combined with one-letter flags. If the alias -v means --opt1=val1 then the following command-line is exactly equivalent to the previous ones:

    myprog -acv infile outfile

UNIX standard arguments confer specific meanings:

• --help means that the program should show the usage/help information and terminate;
• --version means that the program should show the version information and terminate;
• -- means that all subsequent arguments should be treated as values, regardless of any hyphen-prefixes or embedded = signs.

To support such above special processing, CLASP libraries provide facilities for declarative specification of command-line flags and options, and aliases thereof. For the previous example, the CLASP.Ruby code would look like the following:

# file: cr-example.rb

PROGRAM_VERSION = '0.1.2'

Specifications = [

    CLASP.Flag('--all', alias: '-a', help: 'processes all item types'),
    CLASP.Flag('-c', help: 'count the processed items'),
    CLASP.Option('--opt1', alias: '-o', help: 'an option of some kind', values_range: %w{ val1, val2 }),
    CLASP.Flag('--opt1=val1', alias: '-v'),

    # see next section for why these two are here
    CLASP::Flag.Help,
    CLASP::Flag.Version,
]

# assuming the command-line `myprog -acv infile outfile`
Args = CLASP::Arguments.new(ARGV, Specifications)

puts Args.flags.size                # => 2
puts Args.flags[0].name             # => "--all"
puts Args.flags[1].name             # => "-c"

puts Args.options.size              # => 1
puts Args.options[0].name           # => "--opt1"
puts Args.options[0].value          # => "val1"

puts Args.values.size               # => 2
puts Args.values[0]                 # => "infile"
puts Args.values[1]                 # => "outfile"

There are aspects common to all CLI programs, such as responding to --help and --version. All CLASP libraries provide facilities to assist the programmer: CLASP.Ruby provides the two module methods CLASP.show_usage() and CLASP.show_version(), as shown in the following code extending the example above:

Args.flags.each do |f|

    case f.name
    when CLASP::Flag.Help.name

        CLASP.show_usage(Specifications, exit: 0, values: '<input-file> <output-file>')
    when CLASP::Flag.Version.name

        CLASP.show_version(Specifications, exit: 0, version: PROGRAM_VERSION)
    when '--all'

        # do something appropriate to `--all`

    . . .

Given the command

    ./cr-example.rb --help

then the program will output the following

USAGE: cr-example.rb [ ... flags and options ... ] <input-file> <output-file>

flags/options:

    -a
    --all
        processes all item types

    -c
        count the processed items

    -v --opt1=val1
    -o <value>
    --opt1=<value>
        an option of some kind where <value> one of:
            val1,
            val2

    --help
        shows this help and terminates

    --version
        shows version and terminates

and given the command

    ./cr-example.rb --version

then the program will output the following

cr-example.rb 0.1.2

Examples are provided in the examples directory, along with a markdown description for each. A detailed list TOC of them is provided in EXAMPLES.md.

GitHub Page

Defect reports, feature requests, and pull requests are welcome on https://github.com/synesissoftware/CLASP.Ruby.

CLASP.Ruby is inspired by the C/C++ CLASP library, which is documented in the articles:

• An Introduction to CLASP, Matthew Wilson, CVu, January 2012;
• Anatomy of a CLI Program written in C, Matthew Wilson, CVu, September 2012; and
• Anatomy of a CLI Program written in C++, Matthew Wilson, CVu, September 2015.

Other CLASP libraries include:

• CLASP
• CLASP.Go
• CLASP.js
• CLASP.NET
• CLASP.Python

Projects in which CLASP.Ruby is used include:

• libCLImate.Ruby

CLASP.Ruby is released under the 3-clause BSD license. See LICENSE for details.