sub process_file {
	open F, shift;
	# ...do stuff with F...
	close F;
}

sub recurse_dir {
	opendir D, shift;
	while (readdir D) {
		process_file ($_) if -f;
		recurse_dir  ($_)  if -d;
	}
	closedir D;
}

recurse_dir ($ARGV[0]);