User Tracker

#!/bin/sh

MAILTO=$USER # change if you want the mail to go elsewhere

if who | awk '{print $1}' | grep "^$1$" > /dev/null
then
        echo "$1 is currently logged in."
else
until who | awk '{print $1}' | grep "^$1$" > /dev/null
        do
                sleep 5
        done
        echo "This is an automated message from $USER. $1 has logged in." | mail $MAILTO
fi