Need help for basic scripts.. guys

my friend has challenged me does anyone have any input

# Determine if someone is logged on
# Version 4.0
if [ “$#” ne
1 ]
then
echo “ Incorrect number of arguments”
echo “Usage: $ ison4 <user>”
else
user=“$1”
if who | grep “$user” > /dev/null
then
echo “$user is logged on”
else
echo “$user is not logged on”
fi
fi


shell program named ison that will check every 5 seconds whether a particular user has
logged into the system. When the user logs in, print a message on your terminal flagging the login.
(Make sure the user entered is a valid user.) (hint use ison5

cron has a minimum 'resolution' of 1 minute, so you'd need a loop with a sleep 5 to get close to 5 second gaps between checks.