Ruby git hook example - prepare-commit-msg that parses jira ticket name and inserts it and a link in the commit message

prepare-commit-msg

#!/usr/bin/env ruby
# parse jira ticket names out of branches named similar to
#      project-9999-xxxx-xxxx
# project names in the branch can be lowercase
# branches do not have to begin with the project-9999; xxxx-project-9999-xxxx-xxxx will also work
# make sure the hook has permissions to execute after copying it over

message_file = ARGV[0]wi
original_message = File.read(message_file)

# Don't do anything if the commit already has a jira link i.e. in the case of --amend
unless original_message.match(/jira\.example\.com/)
  message = ""

  current_branch = `git rev-parse --abbrev-ref HEAD`
  match = current_branch.match(/([a-zA-Z]*-[0-9]*)-/)

  if match
    jira_ticket = match[1].upcase
    message = message + "[#{jira_ticket}] "
    jira_link = "http://jira.example.com/browse/#{jira_ticket}"
    # Insert jira link immediately before comments begin
    # Match where there are 3 or more lines of comments
    comment_match = original_message.match(/((^\#.*$\n){3})/)
    if comment_match
      jira_link_position = comment_match.offset(0)[0]
    else
      jira_link_position = original_message.length - 1
    end

    # Need an extra line break when message is passed in as -m
    if ARGV[1] == "message"
      jira_link_string = "\n\n#{jira_link}\n"
    else
      jira_link_string = "\n#{jira_link}\n"
    end
    original_message.insert(jira_link_position, jira_link_string)
  end

  message = message + original_message

  File.open(message_file, 'w') { |f| f.write message }
end