Raspberry Pi car-controlling bash script

car.sh

#!/bin/bash

cd /sys/class/gpio

function left {
    echo 4 > export
    echo out > gpio4/direction
    echo $1 > gpio4/value
    echo 4 > unexport
}

function right {
    echo 7 > export
    echo out > gpio7/direction
    echo $1 > gpio7/value
    echo 7 > unexport
}

function forward {
    left 1 && right 1
}

function stop {
    left 0 && right 0
}

function turn_left {
    right 0 && left 1
}

function turn_right {
    right 1 && left 0
}


while true; do
    read -t0.1 -n1 KEY

    case "$KEY" in
        "w")
            forward
            ;;
        "a")
            turn_left
            ;;
        "d")
            turn_right
            ;;
        "s")
            stop
            ;;
    esac
done

stop