How to know if a variable is similar to another

imagining that i have 2 variables similar but not equal , how is the code written to know this ?

I have been trying to figure out how to start but i have no idea .

assumming :

Quote:

var1="Yes i know it for sure" var2="Yes i know is for real"

There are very similarities in these 2 variables , how can this be done without writing the code specifically to these 2 var text .