Identifying an accounts username upon login
CurrentUser="$(env | grep LOGNAME | awk -F = '{print $2}')" and $USER used in a script launched by a launch agent in /Library/LaunchAgents both contain the username of the user logging in. 

CurrentUser="$(users)" contains all users. So the first user will be revealed but logging in with a second user at the same time  (e.g. fast user switching) will break the script.