OpenWrt下的shell脚本解释器与Raspbian下略有区别，这里分享一下树莓派openwrt下的风扇控制脚本：

#!/bin/bash
 echo 14 > /sys/class/gpio/export
 echo out > /sys/class/gpio/gpio14/direction
 echo 1 > /sys/class/gpio/gpio14/value
 sleep 2
 while true
 do
     cputemp=`cat /sys/class/thermal/thermal_zone0/temp`
     valve=70000
     temp=`expr $cputemp`
     echo $temp
     if (( $temp >= $valve ))
     then
         echo 1 > /sys/class/gpio/gpio14/value &
     else
         echo 0 > /sys/class/gpio/gpio14/value &
     fi
     sleep 60
 done

注：

树莓派4官方风扇，通过GPIO14控制通断

valve为阈值，单位为摄氏度的1000倍，valve为70000代表cpu超过70℃时开启风扇