Extract into class & methods and add ability to enter argument to specify branch

go_optional_arg.rb

#!/usr/bin/env ruby
class Go
  attr_accessor :branch_input, :branch_list

  def initialize
    @branch_input = ARGV[0]
  end

  def initialize_branch_name(&block)
    @branch_input ||= begin
      yield if block_given?
      print "\n> "
      gets.strip            
    end
  end

  def run
    run_git_command
    initialize_branch_name do
      output_help
      branch_listing
    end
    select_branch
  end
   
  def output_help
    puts <<-MSG
     
      You can use the number to the left of the branch name or
      an ignorant best match guess can be made to select the branch
      string that you type in.
     
    MSG
  end

  def run_git_command
    @branch_list ||= `git for-each-ref --count=10 --sort=-committerdate refs/heads/ --format='%(refname:short)'`.split("\n")
  end

  def branch_listing
    branch_list.each_with_index do |branch, index|
      puts "#{index}) #{branch}"
    end
  end

  def select_branch
    if branch_input =~ /^\d+$/
      `git checkout #{branch_list[branch_input.to_i]}`
    else
      closest_matches = branch_list.select{|branch| branch.downcase.include? branch_input.downcase }
      if closest_matches.size > 0
        `git checkout #{closest_matches.first}`
      else
        puts "Did not find a branch name that included #{branch_input.downcase}"
      end
    end
  end
end

trap("INT") { puts "\ncatch'ya later"; exit 0 }

Go.new.run