Matching

Can anyone give a sample example of comparing two strings using matching concept in unix shell programming.

say we have two strings,S1 = ravi and S2 = kiran
how can i use matching concept to compare S1 and S2

Can anyone please help me.

# expr hoomer : bart
0
# expr simpson : simpson
7

s1="Ravi"
s2="Kiran"
if [ $s1 != $s2 ]
then
echo "Both are different"
else
echo "Both are same"
fi