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AC_ARG_WITH(firewall,[  --with-firewall=< pf | ipfw | iptables >                          Select the firewall backend],[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], AC_MSG_ERROR([Error: please choose a valid firewall backend (see --help)])    )