git-hook-prepare-commit-msg

#!/bin/bash
# Drop this in a project .git/hooks/prepare-commit-msg

COMMIT_MSG_FILE=$1
COMMIT_SOURCE=$2
# SHA1 is not empty if it's a rebase / ammend
SHA1=$3

# template
# summary
# <blank line>
# ref: <extracted ticket id>
# rest of default commit message
if [ -z "$COMMIT_SOURCE" ] && [ -z "$SHA1" ]; then
MSG="

ref: $(git branch --show-current | grep -E --only-matching '^LL22-[0-9]+')
"
fi

MSG="$MSG$(cat $COMMIT_MSG_FILE)"

printf "$MSG" > $COMMIT_MSG_FILE