Git pre-commit hook that prevents committing when the autor name is unknown, null, empty or whitespace

pre-commit

#!/bin/sh
 
# ---------------------------------------------------------------------------- #
# Filename:      .git/hooks/pre-commit                                         #
# Description:   Git pre-commit hook that prevents committing when the autor   #
#                name is unknown, null, empty or whitespace.                   #
# Created by:    Nano Taboada <nanotaboada@msn.com>                            #
# Version:       0.1.0                                                         #
# License:       http://opensource.org/licenses/MIT                            #
# Last updated:  Jun 30, 2015                                                  #
# ---------------------------------------------------------------------------- #

AUTHOR=$(git var GIT_AUTHOR_IDENT) || exit 1
USER_NAME=$(printf '%s\n' "${AUTHOR}" | sed -n 's/^\(.*\) <.*$/\1/p')
USER_EMAIL=$(printf '%s\n' "${AUTHOR}" | sed -n 's/^.* <\(.*\)> .*$/\1/p')
EMAIL_DOMAIN=$(printf "${USER_EMAIL}" | awk -F "@" 'NR==1 {print $2}')

if [ -z "${USER_NAME}" ] ; then
    echo >&2 "[ERROR] Invalid user name: "${USER_NAME}""
    echo >&2 "[ERROR] Author name cannot be null, empty or whitespace."
    echo >&2 "Please check your Git configuration. If you need help visit:"
    echo >&2 "https://git-scm.com/book/tr/v2/Customizing-Git-Git-Configuration"
    exit 1
fi

if [ "${USER_NAME}" == "unknown" ] ; then
    echo >&2 "[ERROR] Invalid user name: "${USER_NAME}""
    echo >&2 "[ERROR] Author name must be specified."
    echo >&2 "Please check your Git configuration. If you need help visit:"
    echo >&2 "https://git-scm.com/book/tr/v2/Customizing-Git-Git-Configuration"
    exit 1
fi