Set commit message with current branch name (useful for JIRA mentions)

prepare-commit_message.sh

#!/bin/sh

# Use case:
# ---------
# Usually while working on a JIRA ticket,
# we would like to put ticket number in commit message.
# It becomes tedious to write the ticket number everytime you commit.
# Why not let the computer do this task for you?
#
# Prerequisite:
# -------------
# `git config --global core.editor vim`
# Or your favourite editor.
#
# Installation:
# -------------
# `vim .git/hooks/prepare-commit_message`
# Copy and paste the content of this file.
# `chmod +x .git/hooks/prepare-commit_message`
#
# Usage:
# ------
# Create branch with same name as JIRA ticket number.
# Say, ticket number is PRJ-576.
# You create branch with name as PRJ-576.
# When you commit, "PRJ-576: " will be set as message.
# You can then add more description to it.

ORIG_MSG=$(cat "$1")

case "$2" in
  # Don't do anything when there is already a message.
  "message"|"template"|"merge"|"commit" )
    ;;

  * )
    # Get current branch, trim unwanted characters and capitalize.
    # Just like JIRA ticket numbers.
    BRANCH=$(git branch | grep '^\*' | sed -e 's/\*.//g' | tr '[a-z]' '[A-Z]')
    echo "$BRANCH: $ORIG_MSG" > "$1"
    ;;
esac