command="init"    # Initialization.

until [ "$command" = "exit" ]
do
    
    echo -n "Enter command or \"exit\" to quit: "
    read command
    echo
        
    case $command in
    ls)
        echo "Command is ls."
    ;;
    who)
        echo "Command is who."
    ;;
    *) 
        if [ $command != "exit" ] 
        then
            echo "Why did you enter $command?"
        fi
    ;;
    esac

done