Another non-Perl solution would be the Unix command "comm" comm -23 file1 file2 would do it. I like comm because you can get lines in file1 and not in 2, in 2 and not in 1 and lines common to both.
Comment on Re: Filtering lines from one file from another
mertserger,
The problem with comm is that it requires the files to be sorted (which they are not). If antonn doesn't need to preserve order than this is a fine solution. It is actually a fairly difficult problem to solve if you self-impose a number of constraints such as order preservation and arbitrarily large files.