Originally by pvande, then forked by JakobR then forked by emintham

As streams of text swirled before the young man's eyes, his mind swam with thoughts of many things. They would have to wait, however, as he focussed his full concentration on the shifting patterns ahead of him. A glint of light reflecting off a piece of buried code caught his eye and any hope he had was lost. For the very moment he glanced aside, the landscape became Different. The young man gave a small sigh and trudged onward in solemn resignation, fated to wander the desolate codebanks in perpetuity.

Differ is a flexible, pure-Ruby diff library, suitable for use in both command line scripts and web applications. The flexibility comes from the fact that diffs can be built at completely arbitrary levels of granularity (some common ones are built-in), and can be output in a variety of formats.

Add this to your gemfile if you use bundler

gem 'differ'

and bundle to install

bundle install

or install it manually

sudo gem install differ

There are a number of ways to use Differ, depending on your situation and needs. Lets examplify:

require 'differ'

@original = "Epic lolcat fail!"
@current  = "Epic wolfman fail!"

There are a number of built-in diff_by_* methods to choose from for standard use:

Differ.diff_by_line(@current, @original)
# => {"Epic lolcat fail!" >> "Epic wolfman fail!"}

Differ.diff_by_word(@current, @original)
# => Epic {"lolcat" >> "wolfman"} fail!

Differ.diff_by_char(@current, @original)
# => Epic {+"wo"}l{-"olcat "}f{+"m"}a{+"n fa"}il!

No problem, you can call diff directly and supply your own boundary string:

Differ.diff(@current, @original) # Implicitly by line by default
# => {"Epic lolcat fail!" >> "Epic wolfman fail!"}

Differ.diff(@current, @original, 'i')
# => Epi{"c lolcat fa" >> "c wolfman fa"}il

Well, you can supply a regex instead of your string if you have to:

Differ.diff(@original, @current, /[a-z]i/)
# => E{"c wolfman f" >> "c lolcat f"}l!

Include a capture group if you want to keep the separator:

Differ.diff(@original, @current, /([a-z]i)/)
# => Epi{"c wolfman f" >> "c lolcat f"}ail!

If you would like something a little more inline you can require 'differ/string' to get some added inline string magic:

@current.diff(@original) # Implicitly by line by default
# => {"Epic lolcat fail!" >> "Epic wolfman fail!"}

Or a lot more inline:

@current - @original # Implicitly by line by default
# => {"Epic lolcat fail!" >> "Epic wolfman fail!"}

Differ.separator = ' ' # Custom string
@current - @original
# => Epic {"lolcat" >> "wolfman"} fail!

Differ.separator = /[a-z]i/ # Custom regex without capture group
@original - @current
# => E{"c wolfman f" >> "c lolcat f"}l!

Differ.separator = /([a-z]i)/ # Custom regex with capture group
@original - @current
# => Epi{"c wolfman f" >> "c lolcat f"}ail!

So we've pretty much got you covered.

Need a different output format? We've got a few of those too:

Differ.format = :ascii  # Default
Differ.format = :color
Differ.format = :html

Differ.format = MyCustomFormatModule

The formatter must respond to the call method that takes an instant of the Change class as an argument and returns a string.

Yeah, we either:

diff = @current - @original
diff.format_as(:color)

Or with your own formatter:

diff = @current - @original
diff.format_as(->(c){c.to_s})

Copyright (c) 2009 Pieter Vande Bruggen.

(The GIFT License, v1)

Permission is hereby granted to use this software and/or its source code for whatever purpose you should choose. Seriously, go nuts. Use it for your personal RSS feed reader, your wildly profitable social network, or your mission to Mars.

I don't care, it's yours. Change the name on it if you want -- in fact, if you start significantly changing what it does, I'd rather you did! Make it your own little work of art, complete with a stylish flowing signature in the corner. All I really did was give you the canvas. And my blessing.

Know always right from wrong, and let others see your good works.