A relatively reliable way to get login user on Linux

get-login-user.sh

#!/bin/bash

# A relatively reliable way to get login user on Linux

user_entry=`getent passwd $(cat /proc/self/loginuid)`
if [ $? -eq 0 ]; then
	login_user=`echo ${user_entry} | cut -d: -f1`
else
	login_user=${SUDO_USER:-${LOGNAME}}
	if [ "${login_user}" = "" ]; then
		login_user=`id -urn`
	fi
fi

echo ${login_user}