Surely the code can be simplified by using a s///g at the top level instead of looping?

$source =~ s/(\[link title:(.*?)\](.*?)\[\/link])/<a href='$3'>$2<\/a>
+/gi;
[download]

The obvious limitation over the original solution is that it doesn't allow one to loop, but perhaps this would work?

while ($source =~ s/\G(\[link title:(.*?)\](.*?)\[\/link])/<a href='$3
+'>$2<\/a>/i) {
  print "complete: $1\ntitle: $2\nurl: $3\n";
}
[download]

--
integral, resident of freenode's #perl