open( DAT, "data.dat" ) or die "Can't open data.dat: $!\n";

my( @left, @right );

while( <DAT> ) {
  chomp;

  if( /^block/ ) {
    push @{$_}, "block" foreach \@left, \@right;
    next;
  }

  my( $left, $right ) = split( /,/ );

  foreach( $left, $right ) {
    s/^\s+//; s/\s+$//;
  }

  push @left, $left; push @right, $right;
}

close( DAT );
[download]