如何创建支持Ruby的shell命令？

Question

I'm creating a gem in which I would like to be able to make a shell command performing a function in the gem. In a more simple context, I need to create a shell script that performs a Ruby function with options when the shell command is triggered. What is a easiest way to do this?

For example:

$ cow moo

would take a cow gem with a script for the cow command and perform the 'moo' function in the Ruby gem.

If I could, I would also like support for common 'options' formatting in the shell:

$ cow -t moo

Which the above example would take an option and apply a script in Ruby to handle it (in this example -t would print 'moo' twice).

If anyone could help we with this it would be a great help. Thanks!

Answer 1

You could create a regular executable Ruby file named cow containing:

#!/usr/bin/env ruby
require 'cow'

Cow.say ARGV.first

Note the first line, which is the shebang line . It tells your shell which program to use in order to interpret the script. This allows the user to simply call cow instead of ruby $(which cow) .

Put your script in the bin directory:

cow/
  bin/
    cow  <- your executable file
  lib/
    cow.rb
    cow/
      say.rb
  cow.gemspec

Now, all you need to do is put that in your gem specification:

Gem::Specification.new 'cow' do |gem|
  gem.executables = %w(bin/cow)
end

During installation, Rubygems will install your gem's binaries somewhere in the user's path, ensuring they can be found.

As for option parsing, the standard library includes optparse , but there are also many gems available.

I created my own option parser, called Acclaim , which I use in my own utilities. Here's a sample:

class Cow::Command < Acclaim::Command
  option :all_caps, '-A', '--all-caps'

  when_called do |options, args|
    text = args.first.to_s
    text.upcase! if options.all_caps?
    Cow.say text
  end
end

In order to test your application, you can simply execute your script:

$ pwd
~/projects/cow
$ ./bin/cow moo
# output here...

However, this requires that you build your gem from the specification and install it locally every time you want to test your changes:

ruby -I ./lib -r cow -e 'puts Cow.version'
0.0.1
gem build cow.gemspec && gem install cow-0.0.1.gem

Bundler makes life easier by inserting your code into the load path automatically. You just have to run your executable through Bundler:

$ bundle exec ./bin/cow moo
# output here...

Answer 2

How about using http://visionmedia.github.com/commander/ ? Never used it before. But it's a gem that makes developing commandline apps easier :) Does the heavy lifting for you.

There is a bunch more over here: https://www.ruby-toolbox.com/categories/CLI_Option_Parsers