bash脚本中有多个参数

Question

I'm new to bash and I've started working on a simple bash script to turn on or off GPIO pins on raspberryPi. I'd like to provide arguments to the script like this: script.sh GPIO_number start/on/off/clean. How do I continue this script the most efficient way? I'm stuck at the second argument.

#!/bin/bash

if [ -z $1 ]; then
        echo "Usage: gpioaction.sh GPIO start/on/off/clean"
        exit 1
fi

if [ -z $2 ]; then
        echo "Usage: gpioaction.sh GPIO start/on/off/clean"
        exit 1
fi

PIN=$1

start=$(echo "$PIN" > /sys/class/gpio/export;echo "out" > /sys/class/gpio/gpio$PIN/direction;echo "1" > /sys/class/gpio/gpio$PIN/value)
on=$(echo "1" > /sys/class/gpio/gpio$PIN/value)
off=&(echo "0" > /sys/class/gpio/gpio$PIN/value)
clean=&(echo "$PIN" > /sys/class/gpio/unexport)

Answer 1

You appear to be 'close' - what you have assigns values to variables (a = output from some command) and will quickly run through all commands; perhaps something like this is closer to what you are looking for:

function gpio_start {
echo "$PIN" > /sys/class/gpio/export
echo "out"  > /sys/class/gpio/gpio$PIN/direction
echo "1"    > /sys/class/gpio/gpio$PIN/value
}
###
case "$2" ### here you could use functions or simple commands lines
in
        start) replace_with_fucntion_or_start_steps ;;
           on) replace_with_fucntion_or_on_steps ;;
          off) replace_with_fucntion_or_off_steps ;;
        clean) replace_with_fucntion_or_clean_steps ;;
            *) echo "Usage: gpioaction.sh GPIO start/on/off/clean" ; exit ;;
esac
###  
Another, closer to what you have example:  

case "$2"
in
        start) gpio_start ;; ## use function for multiple commands
           on) echo "1" > /sys/class/gpio/gpio$PIN/value ;;
          off) echo "0" > /sys/class/gpio/gpio$PIN/value ;;
        clean) echo "$PIN" > /sys/class/gpio/unexport ;;
            *) echo "Usage: gpioaction.sh GPIO start/on/off/clean" ; exit ;;
esac

If you use the case statement then you don't really need your 'second check' using the 'if' statement.

:)
Dale