Git prepare-commit-msg hook to extract issue number from branch name and append to commit message.

prepare-commit-msg

#!/bin/bash

# Adds reference to GitHub issue if available in branch name.
# The issue number should be at the end of the branch name, following
# a hyphen.

# Only proceed if no second parameter is given to the script.
if [ x = x${2} ]; then
  branch=$(git symbolic-ref --short HEAD)
  if [[ $branch =~ .*-([0-9]+)$ ]]; then
    issue_number=${BASH_REMATCH[1]}
    # sed on osx doesn't treat \n in replacement pattern as a new line.
    # If it did we could do this:
    #
    # sed -i.bak -e "1s/^/\n\nSee #$issue_number./" "$1"
    #
    # Instead we have do lots of weird quoting.
    sed -i.bak -e '1s/^/\'$'\n'"\\"$'\n'"See #$issue_number./" "$1"
  fi
fi