Git hook that prepends Jira issue ID from the branch name to the commit message

prepare-commit-msg.sh

#!/usr/bin/env bash
#
# Git hook that appends Jira issue ID from the branch name to the commit message.
#
# e.g. for the branch name `feature/ABC-1234/add-xyz`, the `[ABC-1234]` 
# is added to the commit message as well as summary.
# 
# Installation:
# $ curl -fsSL -o .git/hooks/prepare-commit-msg \
#     'https://gist.githubusercontent.com/dogukancagatay/38792bf7ace99817555389e043ed954a/raw/prepare-commit-msg.sh'
#

COMMIT_MSG_FILE=$1
COMMIT_SOURCE=$2
SHA1=$3

# Extracts the issue key from the branch name
# e.g. feature/ABC-1234/add-xyz -> ABC-1234
JIRA_ISSUE_KEY="$(git symbolic-ref --short HEAD | awk -F/ '$2 ~ /[a-zA-Z]+-[0-9]+/ {print $2}')"

if [ "$SHA1" = "HEAD" ]; then
    echo "Amending commit, skipping JIRA_ISSUE_KEY prepending"
    exit 0
fi

# if it's a fixup! commit, don't add anything
if grep -q "fixup!" "$COMMIT_MSG_FILE"; then
    echo "Fixup commit found, skipping JIRA_ISSUE_KEY prepending"
    exit 0
fi

# if the message already has the JIRA_ISSUE_KEY prepended, don't change anything
if grep -q "\[$JIRA_ISSUE_KEY\]" "$COMMIT_MSG_FILE"; then
    exit 0
fi

# write JIRA_ISSUE_KEY to commit message file
if [ -n "$JIRA_ISSUE_KEY" ]; then
    sed -i.bak "1s;^;\[$JIRA_ISSUE_KEY\]\n\n\n\[$JIRA_ISSUE_KEY\];" "$COMMIT_MSG_FILE"
    rm -rf "$COMMIT_MSG_FILE.bak"
fi