Git hook to append Jira issue number to commit message basing on branch name

commit-msg

#! /bin/bash

# This hook checks if git commit message (first line) contains Jira 
# ticket (for example TEST-123) and if not prepends it to commit message
# based on current branch name (for example from bugfix/TEST-123-quickfix 
# branch name we'll prepend "TEST-123:" to git commit message)

# This script is called by "git commit" with one argument, the name of
# the file that has the commit message. The hook should exit with non-zero
# status after issuing an appropriate message if it wants to stop the
# commit. The hook is allowed to edit the commit message file.

# source: https://gist.github.com/mpawelski/4dfb6d68b803b60e86599ffbb36d8558
# heavily based on: https://gist.github.com/chonton/d7a48828642ea763b8b84141ead40e64/

# Get the name of the current branch.
branchName=$(git symbolic-ref HEAD --short)
branchRegex="(^|[^A-Z])([A-Z]{3,6}-[0-9]{1,5})([^0-9]|$)"

if [[ $branchName =~ $branchRegex ]]; then
    # Grab the jira ticket from the branch name
    jiraTicket="${BASH_REMATCH[2]}"
    jiraRegex="(^|[^A-Z])${jiraTicket}([^0-9]|$)"

    firstLineOfCommitMessage=$(head -n 1 $1)

    if [[ $firstLineOfCommitMessage =~ ^fixup!* ]]; then
        # Special case for commit starting witch 'fixup!...'. 
        # This commit is probably from "git commit --fixup=<commit>" command
        # and you probably want to squash it later with "git rebase -i --autosquash"

        # We do nothing. ':' is null bash command (required if you want "empty" then clasue)
        :
    else
        # If the message already contains jiraTicket, do not change the commit message.
        if [[ $firstLineOfCommitMessage =~ $jiraRegex ]]; then
            :
        else        
            # prepend the jira ticket
            echo "$jiraTicket: $(cat $1)" > $1
        fi
    fi
else
    :
    # I allow having branches without jira issue in name. Just for experimenting.
    # But if you want to be stricter then you can uncomment 
    # below code to prevent commiting and show message why:

    #echo "Branch name does not correspond to JIRA ticket.  Try one of the following"
    #echo "git checkout -b JIRA-number"
    #echo "git branch -m JIRA-number"
    #exit 254
fi