A "commit-msg" hook to prepend a ticket ID to the first line of the commit message, given that the current branch name has a certain format.

commit-msg

#!/bin/bash

# Functions
get_current_branch() {
  local branch_name=$(git symbolic-ref -q HEAD)
  branch_name=${branch_name##refs/heads/}
  branch_name=${branch_name:-HEAD}
  echo "${branch_name}"
}

get_ticket_id() {
  local branch_name="${1}"
  echo "${branch_name}" | perl -ne 'if (/^\w+\/([A-Z]+-\d+)/) { print "$1"; }'
}

prepend_ticket_id() {
  local commit_file="${1}"
  local ticket_id="${2}"
  local temp_file="$(mktemp)"

  local title="$(head -1 "${commit_file}" | sed -E 's/^[A-Z]+-[0-9]+ //')"
  local body="$(tail -n +2 "${commit_file}")"

  echo "${ticket_id} ${title}" > "${temp_file}"
  echo "${body}" >> "${temp_file}"
  mv "${temp_file}" "${commit_file}"
}

# Main
commit_file="${1}"
current_branch="$(get_current_branch)"
ticket_id="$(get_ticket_id "${current_branch}")"

if [ -n "${ticket_id}" ]; then
  prepend_ticket_id "${commit_file}" "${ticket_id}"
fi