my $this = '<thing>
 condition
   condition
    randomness
      other junk
</thing>';

print "before: $this\n\n";
$this =~ s/\n\s*/ /g;
print "after: $this\n";

__END__
before: <thing>
 condition
   condition
    randomness
      other junk
</thing>

after: <thing> condition condition randomness other junk </thing>