'grep的-q“与”尾-f“退出 [英] 'grep -q' not exiting with 'tail -f'

问题描述

我想实现一个脚本，等待在日志文件中的特定信息。一旦消息被记录的话，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.

下面就是我与尾尝试-f 和的grep -q ：

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

的的grep 从没有放弃过，所以它永远等待，即使消息继续的文件中被记录下来。

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

当我运行这个没有 -f 这似乎很好地工作。

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

推荐答案

尾-f 将读取的文件，并显示行以后添加，也不会终止（除非像 SIGTERM 信号发送）​​。 的grep 是不是这里的拦网环节，尾-f 是。 的grep 将从管道读取，直到它被关闭，但它永远不会是因为尾-f 不退出，并保持管开。

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.

一个解决您的问题可能会被（未测试，并很可能表现不佳）：

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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