string comparison

hi

i am writing a small application where a user enters a phrase in the
textfield and i would like to display all the files present in the root
directory which consists of the keyword or keywords entered by the user.

i have used a few comparison functions but i am not getting the expected
result.

$my_file = file_get_contents("filename.html");
what ever the user enters whether it is a single word or few words i would
like to compare with $my_file in a case insensitive manner.

can anyone suggest the best method and how to go about.

thanks.