Takes a branch name like `myBranch_name-with/any^separators#12345` and adds `\n[#12345]` after the first line.

prepare-commit-msg

#!/bin/sh

#
# Automatically add branch name to every commit message except merge commits.
#

COMMIT_MSG=$1

addBranchName() {
   branchPath=$(git symbolic-ref -q HEAD)
   branchName=${branchPath##*/}
   branchId=$(echo $branchName | sed -n 's/.*#\([0-9]\)/\1/p')

   # No branch id
   if [ "" = "$branchId" ] ; then
      echo "$(cat ${COMMIT_MSG})" > "${COMMIT_MSG}"

   # Branch id already in message
   elif cat ${COMMIT_MSG} | grep "\[#$branchId\]" -q; then
      echo "$(cat ${COMMIT_MSG})" > "${COMMIT_MSG}"

   # Add the branch id
   else
      sed -i "2i  \ \n[#$branchId]" ${COMMIT_MSG}
   fi

}


# Don't inject branch IDs when merging
MERGE=$(cat $COMMIT_MSG|grep -i 'merge'|wc -l)

if [ $MERGE -eq 0 ] ; then
  addBranchName
fi