Removing all whitespace lines from a multi-line string efficiently

Question

In C# what\'s the best way to remove blank lines i.e., lines that contain only whitespace from a string? I\'m happy to use a Regex if that\'s the best solution.

EDIT

Answer 1

In response to Will's bounty here is a Perl sub that gives correct response to the test case:

sub StripWhitespace {
    my $str = shift;
    print "'",$str,"'\n";
    $str =~ s/(?:\R+\s+(\R)+)|(?:()\R+)$/$1/g;
    print "'",$str,"'\n";
    return $str;
}
StripWhitespace("test\r\n \r\nthis\r\n\r\n");

output:

'test

this

'
'test
this'

In order to not use \R, replace it with [\r\n] and inverse the alternative. This one produces the same result:

$str =~ s/(?:(\S)[\r\n]+)|(?:[\r\n]+\s+([\r\n])+)/$1/g;

There're no needs for special configuration neither multi line support. Nevertheless you can add s flag if it's mandatory.

$str =~ s/(?:(\S)[\r\n]+)|(?:[\r\n]+\s+([\r\n])+)/$1/sg;