test for existance of external program

What's the recommended way for testing whether some external program
$PROG exists?

:0
* $? $PROG 2>/dev/null [some options to make $PROG do nothing]
{ $PROG exists, and is able to run and exit without error *if*
appropriate options were used }

Is there a better way? I'm trying to test e.g. for a usable version of
awk.

Thanks much,

Volker

-- 
Volker Kuhlmann                 is possibly list0570 with the domain in header
http://volker.dnsalias.net/             Please do not CC list postings to me.

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