git update-hook script for checking versions of cookbooks and rejecting on non version bump

gistfile1.rb

#!/usr/bin/env ruby
# Compares semantic versions of cookbooks, by looking at the metadata.rb file and
# rejects pushes if the cookbook version has not been bumped. If running this
# script from another script, remeber to pass along the parameters to this
# script.
#
# Requires a gem install semantic.

require 'rubygems'
require 'semantic'

refname = ARGV[0]
oldrev  = ARGV[1]
newrev  = ARGV[2]

# Continue if we can't diff
if newrev == ('0' * 40)
  # delete branch
  exit 0
elsif oldrev == ('0' * 40)
  # new branch
  exit 0
elsif not %x(git ls-tree --name-only -r #{oldrev}).match("metadata.rb")
  # If the repo does not contain a metadata.rb file, it's probably not a cookbook,
  # and we should continue.

  #puts "Did not find any metadata.rb file - cannot determine versions."
  #puts "Is this even a cookbook?!"
  #puts "Continuing..."
  exit 0
end

# TODO: cleanup
# Get the versions from the metadata.rb file.
oldrev_array = %x(git cat-file blob #{oldrev}:metadata.rb).split("\n")
newrev_array = %x(git cat-file blob #{newrev}:metadata.rb).split("\n")
oldrev_grep = oldrev_array.grep(/version\s*"(.*)"/)
newrev_grep = newrev_array.grep(/version\s*"(.*)"/)
oldrev_version = oldrev_grep.to_s[/version.*\"(.*)\"/,1]
newrev_version = newrev_grep.to_s[/version.*\"(.*)\"/,1]

old_version = Semantic::Version.new(oldrev_version)
new_version = Semantic::Version.new(newrev_version)

# Could possibly replace ansi escape codes with gem-colorize or something...
unless new_version > old_version
  puts "\e[31mYou tried to push version #{new_version} of your cookbook,\e[0m"
  puts "\e[31mbut that version of the cookbook seems to already exist.\e[0m"
  puts "\e[31mHave you forgotten to bump the version of your cookbook?\e[0m"
  exit 1     # Exit if new_version is not larger than old_version
end