Greenletters: Painless automation and testing for command-line applications


Did you ever use Expect to automate a complex command-line procedure, like an FTP upload? Expect is handy – and very powerful – but for Ruby projects it sure would be nice to be able to automate console apps directly from Ruby.

You may not have known it, but Ruby actually ships with a tiny Expect clone called expect.rb. Unfortunately it’s more of a proof of concept than a fully functional automation tool.

Enter Greenletters. Greenletters begins to bring some of the power of Expect to Ruby, with a simple, straightforward API. For example, here’s a scripted interaction with the classic Colossal Cave Adventure:

  require 'greenletters'

  adv ="adventure", :transcript => $stdout)

  # Install a handler which may be triggered at any time
  adv.on(:output, /welcome to adventure/i) do |process, match_data|
    adv < < "non"

  puts "Starting adventure..."

  # Wait for the specified pattern before proceeding
  adv.wait_for(:output, /you are standing at the end of a road/i)
  adv << "eastn"
  adv.wait_for(:output, /inside a building/i)
  adv << "quitn"
  adv.wait_for(:output, /really want to quit/i)
  adv << "yesn"
  puts "Adventure has exited."

Greenletters also ships with some simple Cucumber steps, so you can immediately start using it to specify the behavior of your command-line apps:

    Given process activity is logged to "greenletters.log"
    Given a process "adventure" from command "adventure"
    Given I reply "no" to output "Would you like instructions?" from process "adventure"
    Given I reply "yes" to output "Do you really want to quit" from process "adventure"
    When I execute the process "adventure"
    Then I should see the following output from process "adventure":
    You are standing at the end of a road before a small brick building.
    Around you is a forest.  A small stream flows out of the building and
    down a gully.
    When I enter "east" into process "adventure"
    Then I should see the following output from process "adventure":
    You are inside a building, a well house for a large spring.

Want to give it a try? Then:

gem install greenletters

And check out the examples/ directory for inspiration. Let me know what you think!


  1. Cool tool. Thanks. Do you know an easy way to capture the output to a variable. I need to do some validation on results.

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