bash脚本--可能语法错误--不确定尝试“直到”循环

Question

你好，伙计们，我正在为我的服务器编写一个wol脚本。当它的启动时，覆盆子圆周率每次执行。

我想这是一个语法错误，但我现在没有解决方案，所以我问你。我在第5行得到一个错误，但不知道如何纠正它。

#!/bin/bash

nas=[ping -c 1 192.192.168.222.5 &> /dev/null ]

until [ $nas = "1" ];do
python wol.py
sleep 2
nas=[ping -c 1 192.192.168.222.5 &> /dev/null ]
done

wol.py是marc balmar的脚本，它发送wol包。

#!/usr/bin/env python
#coding: utf8

# Wake-On-LAN
#
# Copyright (C) 2002 by Micro Systems Marc Balmer
# Written by Marc Balmer, marc@msys.ch, http://www.msys.ch/
# Modified by saarnu for nerdoskop.wordpress.com
# This code is free software under the GPL

import struct, socket, time, os

def WakeOnLan(ethernet_address):

  # Construct a six-byte hardware address

  addr_byte = ethernet_address.split(':')
  hw_addr = struct.pack('BBBBBB', int(addr_byte[0], 16),
    int(addr_byte[1], 16),
    int(addr_byte[2], 16),
    int(addr_byte[3], 16),
    int(addr_byte[4], 16),
    int(addr_byte[5], 16))

  # Build the Wake-On-LAN "Magic Packet"...

  msg = '\xff' * 6 + hw_addr * 16

  # ...and send it to the broadcast address using UDP
  time.sleep(5)
  s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
  s.setsockopt(socket.SOL_SOCKET, socket.SO_BROADCAST, 1)
  s.sendto(msg, ('<broadcast>', 9))
  s.close()

WakeOnLan('C8:60:00:6D:CF:54') # MAC-Adresse der DiskStation

我用powershell编写了类似的代码--这要简单得多--我真的想要复制它或者把它翻译成bash。

$NAS = test-connection -count 1 -quiet 192.168.222.5
if ($NAS -like "False"){
do
{
$Mac = "C8:60:00:6D:CF:54"
$MacByteArray = $Mac -split "[:-]" | ForEach-Object { [Byte] "0x$_"}
[Byte[]] $MagicPacket = (,0xFF * 6) + ($MacByteArray  * 16)
$UdpClient = New-Object System.Net.Sockets.UdpClient
$UdpClient.Connect(([System.Net.IPAddress]::Broadcast),7)
$UdpClient.Send($MagicPacket,$MagicPacket.Length)
$UdpClient.Close()
Start-Sleep -s 5
$NAS = test-connection -count 1 -quiet 192.168.222.5
}
until
(
$NAS -like "True"
)
}

Answer 1

首先，使用http://www.shellcheck.net修复脚本中的语法问题。

用于命令替换的语法是错误的，使用ping的退出代码直接在until-loop中进行修复。

until ping -c 1 192.192.168.222.5 &> /dev/null
do
    python wol.py
    sleep 2
done

应该能解决你的问题。man的ping页面说

如果ping完全没有收到任何回复数据包，那么它将使用代码1退出。如果指定了数据包计数和截止日期，并且在截止日期到来之前收到的数据包少于计数数据包，则它也将退出代码1。如果出现其他错误，则退出代码2。否则退出时使用代码0。这样就可以使用退出代码来查看主机是否还活着。

Answer 2

嘿，你的bash脚本有几个错误，而不仅仅是一个。

#!/bin/bash

# This is a silent ping. The output is redirected to /dev/null. The only visible
# change in user-land will be the exit code, available as $?.
# The exit code "0" means success, the exit code "1" means some error.

ping -c 1 192.192.168.222.5 &> /dev/null

# You need double round parenthesis here to evaluate a comparison.
# Also a comparison, as almost everywhere in programming, is "==" instead of "=".
until (( $? == "0" ));
    do
    python wol.py
    sleep 2
    # There is the silent ping again. Updating $?.
    ping -c 1 192.192.168.222.5 &> /dev/null
done

有关退出代码，请参阅：Exit Shell Script Based on Process Exit Code

对于不同的括号/括号，请参阅通过man bash、How to use double or single brackets, parentheses, curly braces或https://stackoverflow.com/a/9666169/7236811编写的真正好的bash手册。