Command provides a simple object-oriented interface for running shell commands from Ruby.
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DEPRECATED! One of the primary goals of Command was to provide better access to the STDOUT and STDERR output of a command. The goal was to allow the running of one command to produce separate STDOUT and STDERR strings as well as an accurate, combined output. Combining the output now seems impossible to do with 100% accuracy while also maintaining separate output for each stream. Expect that Command will be removed from GitHub in six months.

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In Ruby, there are plenty of ways to run simple commands:

  • `date`
  • %x(date)
  • exec("date")
  • system("date")
  • Open3.capture2("date")
  • Open3.capture2e("date")
  • Open3.capture3("date")

And those are just a few of the ways built into Ruby's Standard Library!

The Problem

Each of these commands works differently. This can cause confusion for the developer.

In addition, there are often cases where a developer will draw a boundary at shelling out in the test suite. If your codebase uses a mix of all of the methods above, stubbing that boundary is difficult and brittle. The decision to change from Open3.capture3 to Open3.capture2 should not break your tests.

The Solution

All of the methods above have one thing in common: they only require one string argument.

Command provides a simple, object-oriented interface for running simple commands."date")

And that's all!

But if you need more information about what happened, the return value is a Command object with all the goodies that you would expect.

command ="date")
command.stdout   # => "Tue Nov 26 14:45:03 EST 2013\n"
command.stderr   # => ""
command.status   # => 0
command.success? # => true      # => 32157

Now, drawing boundaries in your tests is easy.

describe DateGetter do
  describe ".get" do
    it "gets the date" do
      date = "Tue Nov 26 14:45:03 EST 2013"

      expect(Command).to receive(:run).with("date") do
        double(:command, success?: true, stdout: "#{date}\n")

      expect(DateGetter.get).to eq(date)


Command is open source and contributions from the community are encouraged! No contribution is too small. Please consider:

  • adding an awesome feature
  • fixing a terrible bug
  • updating documentation
  • fixing a not-so-bad bug
  • fixing typos

For the best chance of having your changes merged, please:

  1. Ask us! We'd love to hear what you're up to.
  2. Fork the project.
  3. Commit your changes and tests (if applicable (they're applicable)).
  4. Submit a pull request with a thorough explanation and at least one animated GIF.

Thank You!

Thank you to Sven Fuchs for granting access to the "command" gem name.