open(IN, '<', $source) or die "Couldn't open $source: $!\n";

##</code><code>##

my @data = map [ split ], grep /\S/, <>;  ### <> reads from stdin (or a file named on the command line) You would need <IN> instead.

##</code><code>##

 my @data = map [ split ], grep /\S/, <>;