GetoptLong

The <a href="/ruby/GetoptLong">GetoptLong</a> class allows you to parse command line options similarly to the GNU getopt_long() C library call. Note, however, that GetoptLong is a pure Ruby implementation.

GetoptLong allows for POSIX-style options like --file as well as single letter options like -f

The empty option -- (two minus symbols) is used to end option processing. This can be particularly important if options have optional arguments.

Here is a simple example of usage:

    # == Synopsis
    #
    # hello: greets user, demonstrates command line parsing
    #
    # == Usage
    #
    # hello [OPTION] ... DIR
    #
    # -h, --help:
    #    show help
    #
    # --repeat x, -n x:
    #    repeat x times
    #
    # --name [name]:
    #    greet user by name, if name not supplied default is John
    #
    # DIR: The directory in which to issue the greeting.

    require 'getoptlong'
    require 'rdoc/usage'

    opts = GetoptLong.new(
      [ '--help', '-h', GetoptLong::NO_ARGUMENT ],
      [ '--repeat', '-n', GetoptLong::REQUIRED_ARGUMENT ],
      [ '--name', GetoptLong::OPTIONAL_ARGUMENT ]
    )

    dir = nil
    name = nil
    repetitions = 1
    opts.each do |opt, arg|
      case opt
        when '--help'
          RDoc::usage
        when '--repeat'
          repetitions = arg.to_i
        when '--name'
          if arg == ''
            name = 'John'
          else
            name = arg
          end
      end
    end

    if ARGV.length != 1
      puts "Missing dir argument (try --help)"
      exit 0
    end

    dir = ARGV.shift

    Dir.chdir(dir)
    for i in (1..repetitions)
      print "Hello"
      if name
        print ", #{name}"
      end
      puts
    end

Example command line:

    hello -n 6 --name -- /tmp