Lately I was going through book and talks on "Build Awesome Command-Line Applications in Ruby: Control Your Computer, Simplify Your Life" by David Bryant Copeland.

Major stuff /me noted down from it are as below :

The UNIX Way

• grepable (One "record" perline)
• cutable (delimited "fieIds")
• exit codes! (O for success, nonzero for failure)
• messaging (stderr) vs. output (stdout)

Why Ruby?

• High-level abstractions
• Still close to the metal (eg. FileUtils)
• Fast (no heavyweight VM to start up)
• Simple packaging/distribution with RubyGems

Ruby, The Ecosystem

• CLI is part of the culture
• Great open-source gems for command-line
• Great open-source gems for everything else

How you should do it

• Check exit codes - plays well!
• Log the command helpful!
• Capture the output - helpful!
• Check exit codes plays well!
• Log the command helpful!
• Capture the output- helpful!
• Think of "future you"

Few CIL gems I liked :

• Rainbow - Create colored output
• Thor - Create a command-suite app simply and easily, as well as Rails generators
• GLI - Create awesome, polished command suites without a lot of code
• Slop - Create simple command-line apps with a syntax similar to trollop.
• Childprocess - Cross-platform ruby library for managing child processes
• Formatador - produce rich output with a tag-like string syntax, including tables and progressbars
• Highline - handle user input and output via a “Q&A” style API, including type conversions and validation

All in All it's a pretty decent read and will help one getting started and running CLI apps in a wink ;)