sub file_ext {
		# find the last part of each string
		$a =~ s/.*(\..*)/;
		$a1 = $1; 
		$b =~ s/.*(\..*)/;
		$b1 = $1;
		#split '.', 1, $a;
		#split '.', 1, $b;
		#compare them
		#return $a cmp $b; 
		$a1 cmp $1; 
		}