Today I had to a set of email addresses, one per line, from which I had to remove the addresses of folks that said “Don’t email me.” Those emails were in a separate file, one address per line.

I figured I’d have to do this again, so I wrote a ruby script to automate it. Below, stripper.rb

#put each address in an array, remove whitespace and make it all lowercase
 potential_emails = IO.readlines("potentials.txt").map! {|email| email.strip.downcase}
 delete_emails = IO.readlines("donotemail.txt").map! {|email| email.strip.downcase}

#use the beauty of ruby's array subtraction operator
 puts potential_emails - delete_emails

Simple, terse and readable.  Lovely!