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# Check whether --with-firewall or --without-firewall was given.
if test "${with_firewall+set}" = set; then
  withval="$with_firewall"

 FWALLSDIR="/my/path" && case "${withval}" in
     pf)
        cp $(FWALLSDIR)/command_pf.h $(FWALLSDIR)/command.h
        usepf=true
        ;;
     ipfw)      useipfw=true ;;
     iptables)
        cp $(FWALLSDIR)/command_iptables.h $(FWALLSDIR)/command.h
        useiptables=true
        ;;
     *)
        echo "Choose a valid firewall backend (see --help)"
        exit 1
        ;;
    esac
else
  { { echo "$as_me:$LINENO: error: Error: please choose a valid firewall backend (see --help)" >&5
echo "$as_me: error: Error: please choose a valid firewall backend (see --help)" >&2;}
   { (exit 1); exit 1; }; }
    
fi;

...