; my @prev_line; while ( ) { my @this_line = split /[,\s]+/; shift @this_line; if ( @prev_line ) { my @output; for ( 0 .. $#this_line ) { push @output, "$this_line[$_]-$prev_line[$_]"; } print join( ", ", @output ), "\n"; } @prev_line = @this_line; }