You could solve that with substrings and lc / uc. Just compare the entered string with the a substring from the menu options, starting at 0 and having the same length your entered string has. Convert both strings to lower (or upper) case before comparing.

Or you could compare each menu string with /^$entered_string/i. But take care to quotemeta the entered string so that entering "." or ".*" doesn't confuse your program.