Git update hook to disallow fast-forwards for master and release branches

gistfile1.rb

#!/usr/bin/env ruby

$refname = ARGV[0]
$oldrev  = ARGV[1]
$newrev  = ARGV[2]
$user    = ENV['USER']

puts "Enforcing Policies... \n(#{$refname}) (#{$oldrev[0,6]}) (#{$newrev[0,6]})"

NON_FASTFORWARD_BLACKLIST = [/\brelease\b/, /\bmaster\b/]

# enforces fast-forward only pushes 
def check_fast_forward
  if NON_FASTFORWARD_BLACKLIST.any?{ |b| $refname =~ b}
    missed_refs = `git rev-list #{$newrev}..#{$oldrev}`
    missed_ref_count = missed_refs.split("\n").size
    if missed_ref_count > 0
      puts "[POLICY] Cannot push a non fast-forward reference"
      exit 1
    end
  end
end

check_fast_forward

Make sure you mark it as executable

It should live in .git/hooks and be named 'update'