Prepend issue number to commit message without duplicating it in special cases such as amend or rebase

commit-msg.sh

#!/bin/bash
# Adds JIRA issue key from branch name to commit message.
# Takes into account the possibility that the key is already in the message (e.g.
# when rebasing or amending existing commits).

REGEX_ISSUE_ID="((?!([A-Z0-9a-z]{1,10})-?$)[A-Z]{1}[A-Z0-9]+-\d+)"

get_issue_id_from_string()
{
    echo "$1" | LC_ALL=en_US.utf8 grep -o -P "$REGEX_ISSUE_ID"
}

# Find current branch name
BRANCH_NAME=$(git symbolic-ref --short HEAD)

if [[ -z "$BRANCH_NAME" ]]; then
    echo "No branch name... "; exit 0
fi

# Extract issue id from branch name
ISSUE_ID=$(get_issue_id_from_string "$BRANCH_NAME")

if [[ -z "$ISSUE_ID" ]]; then
    # No issue ID found. Do nothing
    exit 0
else
    SHORT_MSG=$(head -n 1 "$1")
    MSG=$(cat "$1")
    ID=$(get_issue_id_from_string "$SHORT_MSG")

    # Prepend issue ID only if it is not already in the message
    if [[ -z "$ID" ]]; then
        echo -n "[$ISSUE_ID]: " > "$1"
        echo "$MSG" >> "$1"
    fi
fi