"regular expressions" if a very vague term.
There are many different text functions that can be used to analyze text in FileMaker. Since you don't give an example of what you need to analyze, that's about all I can say except to note that you can look up "text Functions" in FileMaker help to pull up a list of what's there and to look up the syntax and return results for each.
Regular Expressions (Grep and RegEx), aren't wired in to Filemaker, but Shawn Flisakowski created some fine custom functions to replicate them, which you can import if you have FMP Advanced. He also included some good examples at http://www.spf-15.com/fmExamples/. The specific file you should download is under Perl-Style Regular Expressions inside FM Pro 7.