重击:循环直到命令退出状态等于0 [英] Bash: Loop until command exit status equals 0

问题描述

我在本地计算机上安装了netcat，并在端口25565上运行了服务.使用命令:

I have a netcat installed on my local machine and a service running on port 25565. Using the command:

nc 127.0.0.1 25565 < /dev/null; echo $?

Netcat检查端口是否打开，如果打开则返回0，如果关闭则返回1.

Netcat checks if the port is open and returns a 0 if it open, and a 1 if it closed.

我正在尝试编写一个bash脚本以进行无限循环，并每秒执行一次以上命令，直到命令的输出等于0(端口打开)为止.

I am trying to write a bash script to loop endlessly and execute the above command every second until the output from the command equals 0 (the port opens).

即使端口打开(1变为0)，我当前的脚本也一直不断循环"...".

My current script just keeps endlessly looping "...", even after the port opens (the 1 becomes a 0).

until [ "nc 127.0.0.1 25565 < /dev/null; echo $?" = "0" ]; do
         echo "..."
         sleep 1
     done
echo "The command output changed!"

我在做什么错了?

推荐答案

保持简单

until nc -z 127.0.0.1 25565
do
    echo ...
    sleep 1
done

只需让shell隐式处理退出状态

shell可以通过显式和隐式两种方式处理退出状态(记录在 $?中).

The shell can deal with the exit status (recorded in $?) in two ways, explicit, and implicit.

显式: status = $?，可以进行进一步处理.

Explicit: status=$?, which allows for further processing.

隐含:

对于每个陈述，在您的脑海中，在单词成功"之后添加到命令，然后添加 if ，直到或 while 在它们周围构造，直到该短语有意义为止.

For every statement, in your mind, add the word "succeeds" to the command, and then add if, until or while constructs around them, until the phrase makes sense.

直到nc 成功 ；做 ...;完成

-z 选项将阻止 nc 读取stdin，因此不需要</dev/null 重定向.

The -z option will stop nc from reading stdin, so there's no need for the < /dev/null redirect.

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