Filtering Custom Form Fields on Length and Character Types

Hi Everyone!

We are working on a scenario that will show us issues that were submitted with a custom form field that has a length greater or less than 8 and/or contain letters. We have the first part done, but we can't find a way to find ones that contain letters. We thought of implementing a regular expression to find them but we can't find a module that allows that.

Any help or insight would be greatly appreciated