[App_rpt-users] Running a shell script from a DTMF command?

[Phil N6TCT]

Hi gang.  Basic question here: what is the magic incantation to run an
arbitrary shell script from a DTMF command to an asterisk app_rpt
system?  E.g., I want to be able to dial *99999 or something and have
my asterisk system run /usr/local/bin/whatever.  I figure there has to
be a way to do this, but I haven't been able to spot it.  Thanks!

Phil, N6TCT