file_exists and wildcard/regex

What is the preferred method with php to test and see if a file [pattern] exists? For example, i only need to search in one directory, that may have any number of files named such as afile1.txt, afile2.txt, afile3.txt, .... And also, bfile1.txt, bfile2.txt, bfile3.txt, ... I want to see if any such file 'family' exists. That is, i want to see if there is any file named bfile[1-9][0-9]+.txt. I don't care which bfile number exists, i just want to know if any bfile exists. I hope this is clear enough, if not let me know. thanks, dK