How to test if a substring exist in a string?

How do I test if a sub-string exist in a string variable without having to write a while loop with CUT and compare?

For exmaple:
If I have a variable that looks like VAR1=1234-5678-9012-3345-5278 and I have another variable VAR2=5678. I want in the dialplan to test if VAR2 exist in VAR1, or that the VAR2 pattern is contained in VAR1.

Hope it is clear.