prepare-commit-msg

#!/usr/bin/env ruby

# place in .git/hooks/prepare-commit-msg                                       

branch_name = `git rev-parse --abbrev-ref HEAD`
commit_file = ARGV.first

first_line = File.open(commit_file, &:readline)

if first_line.strip.empty? && (match = branch_name.match(/(^.*\d+)/i))
  # Assumes a ticket number ends in a number for e.g. #1, PROJECT_NAME-3
  commit_prefix = match.captures.first.upcase

  previous_commit_msg = File.read(commit_file)

  File.open(commit_file, 'w') do |f|
    f.puts commit_prefix
    f.puts previous_commit_msg
  end
end