bash脚本代码未正确运行[重复]

Question

下面的代码不能正常工作，总是打印第一个elif的echo。这是在bbb上运行的。有人能找到错误吗？我知道这很愚蠢，但我找不到。

#!/bin/bash

#bashUSR.sh


path=/sys/class/leds/beaglebone:green:usr

echo "starting the LED bash script."

if [ "$#" == 0 ]; then
        echo "to few arguments. enter either 0 or 1 followed by on or off."
        exit 2

elif [ "$2" != "on" ] || [ "$2" != "off" ]; then
        echo "invalid second argument. please input either on or off."

elif [ "$1" == "0" ] && [ "$2" == "on" ]; then
        echo "turning on usr0 LED."
        export path0/brightness 1

elif [ "$1" == "0" ] && [ "$2" == "off" ]; then
        echo "turning off usr0 LED."
        export path0/brightness 0

elif [ "$1" == "1" ] && [ "$2" == "on" ]; then
        echo "turning on usr1 LED."
        export path1/brightness 1

elif [ "$1" == "1" ] && [ "$2" == "off" ]; then
        echo "turning off usr1 LED."
        export path1/brightness 0

else
        echo "invalid user number. please input a number between 0 and 1."
fi

Answer 1

替换：

elif [ "$2" != "on" ] || [ "$2" != "off" ]; then
        echo "invalid second argument. please input either on or off."

与：

elif [ "$2" != "on" ] && [ "$2" != "off" ]; then
        echo "invalid second argument. please input either on or off."

这个逻辑测试总是正确的：

[ "$2" != "on" ] || [ "$2" != "off" ]

无论$2的值是多少，上述两个测试中的一个将为真。因为这两者都是用逻辑or连接的，所以整个语句都是正确的。

我怀疑你想要的是：

[ "$2" != "on" ] && [ "$2" != "off" ]

让我们测试一下$2的三个值：

for x in on off other
do
    set -- 1 "$x"
    if [ "$2" != "on" ] && [ "$2" != "off" ]
    then
        echo "$2 is bad"
    else
        echo "$2 is OK"
    fi
done

以上代码产生：

on is OK
off is OK
other is bad