Your comment suggests that the program is waiting for /usr/local/script/netdiag to write something.

Which may mean the "problem" (or rather, the fix) lies in said program - not in your small script.

Considering this is a networking program - perhaps netdiag is expecting $CR$LF as line endings, not just $CR (why $CR there, not $LF?). It hasn't seen a full line yet, so it's not going to write anything.