You should try comp.unix.shell newsgroup for shell, including korn shell (or simply ksh), questions instead of this site related to things Perl.

In any case ...

#!/usr/bin/ksh
uid=${uid:-/etc/passwd}
[download]

Why not just set $uid directly (uid='/etc/passwd')?

/etc/passwd/read
$ cut-d: -f1 < uid gt $$
[download]

Just what are you trying to do there? Does your script run to completion successfully (not that it gives a result)?