Old Guy New Trick

An old guys journey to learn how to code.

Ruby, RVM, Cmd Line SheBang!

Author: John on February 12, 2014

I ran across this tip while reading the book "Build Awesome Command-Line Applications in Ruby 2," by David Bryant Copeland.  Although most of the code I've been practicing
has been Ruby on Rails, at my day job we utilize a lot of command line applications.  I'm on a mission to add Ruby to our toolbox which currently is Perl and shell scripts.

For a recent project I needed a command line application that could take a CSV file as an input, extract out some data, and create a new pipe (|) delimted text file.  I use RVM on my personal laptop and desktop, so I installed it on our company server.  At that time, Ruby was at version 1.93.  Not too long after, I added 2.0.0 and 2.1.0.  But my application was written in 1.93.  It is a simple application so the version shouldn't matter.  But in case it does, you may find value in this tip.

If you are a RVM user, and type the command 'which ruby' at the command line, you may get something similar to:


You can use that as the first line of your ruby script:


However, if you want your script to use whatever the current version of Ruby is, or if Ruby is in a different location on a machine other than yours, you can use this syntax:

#!/usr/bin/env ruby

This tip is found on page 4, in the section: "Shebang: How the Systems Knows an App Is A Ruby Script"

Learn Something New Everyday

Last Edited by: John on December 29, 2015