How to find substring in string bash

I have url like or stored in a shell variable named my_url or array. How do I check if a string contains a substring such as app1 or app2 in Bash? Can I do grep app1 $my_url? The grep one is not working out for me. Hence, I wanna know How to find substring inside a string and how to grep a variable?

Try the case…esac statment

case "$my_url" in
    *app1* ) echo "app1 found";;
    *app2* ) echo "app2 found";;
    * ) echo "Error, app1 or app2 not found in $my_url";;

See my tutorial page