dispatch.sh

#!/bin/bash

cmd=$(echo "" | dmenu -p "hello: ")

case "$cmd" in
    run)
        exe=`dmenu_path | dmenu ${1+"$@"}` && exec $exe
        ;;
    =*)
        expression=${cmd:1}
        result=$(expr $expression)
        echo "" | dmenu -p $result
        ;;
    *)
        exit
        ;;
esac