Knowledge Base

How to use the Interactive Ruby Shell to troubleshoot gems

The Interactive Ruby Shell (irb) is a tool that enables you to interactively run Ruby programs and statements from the command line. This article describes how to use the Interactive Ruby Shell to troubleshoot Ruby gem loading and configuration.

Basic Interactive Ruby Shell (irb) usage

To start irb, log in to your account using SSH, and then type the following command:

irb

To debug a specific Ruby program, type the following command, where program.rb represents the name of the program you want to run:

irb program.rb

The default irb command prompt appears:

irb(main):001:0>

From the irb prompt, you can run any Ruby statement and see the result immediately. For example, to view the value of the $0 global variable (which stores the name of the current Ruby program being run), type the following command:

p $0

To exit irb, type the following command:

exit

Troubleshooting Gems

You can use irb to verify the Ruby environment is set up correctly for your gems. To do this, follow these steps:

  1. At the command prompt, type the following command to start irb:
    irb
  2. At the irb prompt, type the following commands. Replace gem_name with the name of the gem that you want to test:

    require 'rubygems'
    require 'gem_name'
    
    For Ruby version 1.8, you must require rubygems before any other gems.
  3. You receive one of the following results:

    • => true

      This result indicates that the environment is set up correctly, and Ruby is able to load the specified gem.

    • LoadError: no such file to load -- gem_name
      

      This result indicates that the environment is not set up correctly, and Ruby is unable to load the specified gem.

  4. If you receive a LoadError message in step 3, type the following command:

    p $LOAD_PATH

    The $LOAD_PATH global variable stores an array that contains all of the directories Ruby searches when the load or require methods are called. Verify that the path to your gems is in $LOAD_PATH. If it is not, you must configure the GEM_HOME and GEM_PATH environment variables to ensure the gems load correctly.

    For step-by-step instructions about how to configure Ruby gems on an A2 Hosting account, please see this article.

More Information

For more information about the Interactive Ruby Shell, please visit http://ruby-doc.com/docs/ProgrammingRuby/html/irb.html.