'grep -q' 不以 'tail -f' 退出 [英] 'grep -q' not exiting with 'tail -f'

问题描述

我正在尝试实现一个脚本来等待日志文件中的特定消息.记录消息后，我想继续脚本.

I am trying to implement a script that wait for a specific message in a log file. Once the message is logged then I want to continue the script.

这是我尝试使用 tail -f 和 grep -q 的内容:

Here's what I am trying out with tail -f and grep -q:

# tail -f logfile | grep -q 'Message to continue'

grep 永远不会退出，因此即使文件中记录了继续消息"，它也会永远等待.

The grep never quit and so it waits forever even if 'Message to continue' is logged in the file.

当我在没有 -f 的情况下运行它时，它似乎工作正常.

When I run this without -f it seems to work fine.

推荐答案

tail -f 将读取文件并显示稍后添加的行，它不会终止(除非像 SIGTERM 这样的信号 发送).grep 不是这里的阻塞部分， tail -f 是.grep 会从管道中读取数据，直到管道关闭，但这永远不会是因为 tail -f 不会退出并保持管道打开.

tail -f will read a file and display lines later added, it will not terminate (unless a signal like SIGTERM is sent). grep is not the blocking part here, tail -f is. grep will read from the pipe until it is closed, but it never is because tail -f does not quit and keep the pipe open.

您的问题的解决方案可能是(未经测试并且很可能表现不佳):

A solution to your problem would probably be (not tested and very likely to perform badly):

tail -f logfile | while read line; do
  echo $line | grep -q 'find me to quit' && break;
done

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