linux - bash sh 差异，脚本转换

Question

我有这个用 bash 编写的脚本

#!/bin/sh

# script makes grep directly on dmesg output
# looking  for  'USB disconnect'  phrase  if
# it  finds  it  then  machine  is  rebooted
# ver 1.2
clear

UNPLUG_MESSAGE="PLEASE UNPLUG THE USB STICK NOW"
echo $UNPLUG_MESSAGE && sleep 2

while true; do

USB_STATUS=`dmesg | tail -n 5 |  grep 'disconnect'`

  if [[ $USB_STATUS == *USB?disconnect* ]]
     then
        clear && echo "Rebooting... bye" 
    sleep 1 && sudo reboot

  elif [[ $USB_STATUS != *USB?disconnect* ]]
     then
        clear && echo "Please remove USB drive..."
        sleep 2
  fi
done

exit 0

将#!/bin/bash 更改为#!/bin/sh 后，该脚本不再起作用 - 我应该在此脚本中更改什么？

我遇到了未知操作数 USB?disconnect、./reboot.sh: 16: ./reboot.sh: [[: not found 等错误

Answer 1

在 ubuntu 上 sh 是 dash (您可以运行 ls -l $(which sh) 来查看)。

在dash没有 [[(双括号)运算符。您必须仅使用 test 内置函数或 [(单括号)。

你可以替换:

if [[ $USB_STATUS == *USB?disconnect* ]]
...
elif [[ $USB_STATUS != *USB?disconnect* ]]

通过:

if [ $(echo $USB_STATUS | grep -c "USB disconnect") != 0 ]
...
elif [ $(echo $USB_STATUS | grep -c "USB disconnect") = 0 ]