使用“手表"在Bash中重复运行功能? [英] Using "watch" to run a function repeatedly in Bash?

问题描述

这是我的第一个Bash脚本.我的Debian机器出现WiFi问题.我不是要问起因，而是要对Bash的问题进行创可贴.我的WiFi会随机消失，通常每12-15分钟消失一次.我在此服务器上使用SSH，不需要从物理服务器手动运行 ifdown wlan0 和 ifup wlan0 (重新连接WiFi).

This is my first Bash script. I have a WiFi issue with my Debian machine. I'm not here to ask about the cause, but rather how to put a band-aid on the issue with Bash. My WiFi will drop out at a random time, usually every 12-15 minutes. I use SSH on this server, and do not want to have to run ifdown wlan0 and ifup wlan0 (which reconnects the WiFi) manually from the physical server.

此Bash脚本的功能是尝试连接3次.如果失败三次，它将放弃.否则，每三秒钟它将通过尝试ping Google来检查我的服务器是否已连接.

The function of this Bash script is to attempt to connect three times. If it fails three times, it will give up. Otherwise, every three seconds it will check whether or not my server is connected by attempting to ping Google.

#!/bin/bash

ATTEMPTS=1

function test_connection {
  ping -c 1 www.google.com
  local EXIT_CODE=$?
  if [ $EXIT_CODE -eq 0 ]
    then
      return true
    else
      return false
  fi
}
function reset_connection {
  ifdown wlan0
  ifup wlan0
  EXIT_CODE=$((EXIT_CODE+1))
}
function connection_test_loop {
  if [ $ATTEMPTS -ge  3 ]
    then
      echo CONNECTION FAILED TO INITIALIZE ... ATTEMPT $ATTEMPTS FAILED ... EXITING
      exit
  fi
  if ! [ test_connection ]
    then
      echo CONNECTION DROPPED ... ATTEMPTING TO RE-ESTABLISH CONNECTION ... ATTEMPT $ATTEMPTS
      reset_connection
  fi
}

test_connection
if [ $? ]
  then
    echo CONNECTION PRE-ESTABLISHED
    watch -n 3 connection_test_loop
  else
    echo CONNECTION FAILED TO INITIALIZE ... ATTEMPTING TO RESET CONNECTION ... ATTEMPT $ATTEMPTS
    reset_connection
    if [ $? ]
      then
        echo CONNECTION ESTABLISHED
        watch -n 3 connection_test_loop
      else
        echo CONNECTION FAILED TO INITIALIZE ... ATTEMPT $ATTEMPTS FAILED ... EXITING
        exit
    fi
fi

我已经隔离了此脚本存在的问题.它在于使用 watch 调用 connection_test_loop 函数.我一直无法找到任何有关为什么它无法按预期执行并每三秒钟运行一次功能的信息.

I've isolated the issue I'm having with this script. It lies in calling the connection_test_loop function with watch. I've been unable to find any information as to why this isn't performing as expected and running the function every three seconds.

推荐答案

watch 可能不知道您的connection_test_loop函数.您可以尝试在下面添加 export test_connection也许可以解决问题:

It's possible that watch is not aware of your connection_test_loop function. You can try adding an export below the test_connection to perhaps solve the issue:

test_connection
export -f connection_test_loop
...

↳ http://linuxcommand.org/lc3_man_pages/exporth.html

调用 watch 时，您可能需要以下语法:

When calling watch, you may need this syntax:

watch -x bash -c connection_test_loop

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