Building command line applications in Ruby

Let’s build a (simple) calculator ● addition ● subtraction ● multiplication

Why? We can build small, stand alone applications without worrying about introducing too much all at the same time.

Reading from the command line We can read numbers from the command line, and put them into our application to do addition, subtraction and multiplication upon.

ARGV “ARGF is a stream designed for use in scripts that process files given as command-line arguments or passed in via STDIN. The arguments passed to your script are stored in the ARGV Array, one argument per element. ARGF assumes that any arguments that aren't filenames have been removed from ARGV.”

./add.rb 1 2 3

ARGV == [“1”, “2”, “3”]

“1” is not a number

Add all the numbers sum = 0 ARGV.each do |arg| sum += arg.to_i end puts sum

Creating an executable script #!/usr/bin/env ruby

Creating an executable script chmod +x add.rb

Putting it all together ./add.rb 1 2 3 => 6

more?

questions?