; my @prev_line; while ( ) { my @this_line = split /[,\s]+/; shift @this_line; print join( ", ", map { "$this_line[$_]-$prev_line[$_]" } 0 .. $#this_line ), "\n" if @prev_line; @prev_line = @this_line; } __DATA__ date, val1, val2, val3, val4 1/2/2007, 1, 4, 5, 6 1/3/2007, 2, 5, 7, 10 1/5/2007, 5, 6, 8, 11