c:\@Work\Perl\monks>perl -wMstrict -le
"my @lines = (
   qq{line1\n}, qq{line2\n}, qq{\n}, qq{line4\n}, qq{ \t\n},
   qq{\t \t \n}, qq{line7\n}, qq{line8\n},
   );
 print qq{[[@lines]]};
 ;;
 @lines = grep !m{ \A \s* \Z }xms, @lines;
 print qq{<<@lines>>};
"
[[line1
 line2

 line4


 line7
 line8
]]
<<line1
 line2
 line4
 line7
 line8
>>