[exim] How to set option using output from system command?

How to set option using output from system command?

deliver_queue_load_max = ${run{/bin/grep 'processor' /proc/cpuinfo -c}}

fixed-point number expected for deliver_queue_load_max


deliver_queue_load_max = ${run{/bin/grep 'processor' /proc/cpuinfo -c}}{$value}

fixed-point number expected for deliver_queue_load_max


deliver_queue_load_max = ${run{/bin/grep 'processor' /proc/cpuinfo -c}{$value}}

fixed-point number expected for deliver_queue_load_max