You can use Marcus’s answer (* wildcards) outside a case statement, too, if you use double brackets:
string='My long string' if [[ $string == *"My long"* ]]; then echo "It's there!" fi
Note that spaces in the needle string need to be placed between double quotes, and the
* wildcards should be outside. Also note that a simple comparison operator is used (i.e.
==), not the regex operator