Add ticket number from the branch to commit messages

prepare-commit-msg

#!/bin/sh
#
# Automatically adds branch name and branch description to every commit message.
# Skips this step if the commit message already starts with "[".
# Modified from the stackoverflow answer here: http://stackoverflow.com/a/11524807/151445
#

# Succeed on all merge messages, as evidenced by MERGE_MSG existing
[ -f $GIT_DIR/MERGE_MSG ] && exit 0

# Get branch name and description
NAME=$(git branch | grep '*' | sed 's/* //')
DESCRIPTION=$(git config branch."$NAME".description)

ticket="$(git rev-parse --abbrev-ref HEAD)"
[[ $ticket =~ (([[:alnum:]]{3,})-([[:digit:]]{3,})).* ]] && ticketID=${BASH_REMATCH[1]}
if [ -n "$ticketID" ]
then
  # Debug:
  # printf "%s\n" "$ticketID: "
  # Don't apply this logic if we are in a 'detached head' state (rebasing, read-only history, etc)
  # newlines below may need echo -e "\n\n: (etc.)"
  if [ "$NAME" != "(no branch)" ] && [[ "$(cat $1)" != [* ]]; then
    	# Append branch name and optional description to COMMIT_MSG
  	# For info on parameters to githooks, run: man githooks
	echo "[$ticketID] $(cat $1)" > "$1"
  fi
fi

How to add the hook to your repos is described in this article.