hi guys

Need some help on my below script

#!/bin/sh
if [ -f /root/joy/inittab ]
then
echo "~~:S:wait:/sbin/sulogin" >> /root/joy/inittab
else
echo "/root/joy/inittab does not exist"
fi

now the problem is that when i run the above script it runs successfully
but when i run it repeatedly the word echo "~~:S:wait:/sbin/sulogin" gets added to the file irrespectively the no of times i run the script.
I jst want the line created jst once in the file irrespective of times i run the script.How do i do pls help and thanks in advance

reg:ash