Locating files using wildcards

Hi,

I'm trying to locate a file by wildcard (I know the path, I'm just searching for a fine inside that directory), but I can't seem to find a way to do this. For example, say I have the following files:

file1.txt
file2.txt

I want to be able to locate them with just looking for "file*.txt" or something similar with regular expressions. However, I don't want to have more than one match, so the above example would either fail or somehow indicated that there was more than one match.

Thanks!