... and you should be testing the return value of unlink since it can fail :-)

Something like this should work (untested code):

@keep{@files} = (1) x @files;
foreach my $file ( @filelist ) {
   next unless $keep{$file};
   unlink $file == 1 or warn "could not unlink $file ($!)\n";
}
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(yes, I know that you could just test unlink for truth/false in this instance - but I always like to remind myself that it returns the number of successful deletions rather than success/failure).