Ruby unified diff using tmp files

rob 26 Mar 2010

This is admittedly ghetto, but I needed a super simple small-scale solution to creating unified diffs based off large blocks of text. The easiest way to do this was by creating temp file and using the native diff command to do the comparison.

I’ve used this method for a really small snippets app for our intranet, which can be found on GitHub.

require 'tempfile' # TODO: do some pre-comparison on a and b so we can skip creating temp files and all that jazz. # NOTE: this is so ghetto ;) module Diffable def diff(b, options = {}) Diff.new(self, b, options).diff end end class Diff attr_reader :output, :changed alias_method :changed?, :changed alias_method :to_s, :output def initialize(a, b, options = {}) @a = a.to_str @b = b.to_str @options = options @changed = false @output = '' end def diff file_a = string_to_file('a', @a).path file_b = string_to_file('b', @b).path @output = format_output(`diff --unified=-1 #{file_a} #{file_b}`) @changed = !@output.strip.empty? self end def to_html(options = {}) diff.output.each_line.inject("") do |output, line| output + \ case line[0] when '@' "<div class='#{options[:meta_class] || 'diff_meta'}'>#{line}</div>" when '-' "<div class='#{options[:sub_class] || 'diff_sub'}'>#{line}</div>" when '+' "<div class='#{options[:add_class] || 'diff_add'}'>#{line}</div>" else line end end end def to_s output end private def string_to_file(key, data) Tempfile.open("#{key}.tmp_diff") do |file| file << data.to_str end end def format_output(output) output.gsub! /\-{3}.+/, "--- #{@options[:mine]}" if @options[:mine] output.gsub! /\+{3}.+/, "+++ #{@options[:theirs]}" if @options[:theirs] output end end class String include Diffable end

It can use some work (definitely use some work), but it gets the job done. I’ve also tried to fit this diff library into the build, but it wasn’t what I was looking for at the time.

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Ruby unified diff using tmp files

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