需要有关另一个 grep 命令输出的 grep 帮助
我有一个文件 test.log。非常大的日志文件。它有不同级别的日志记录。例如，trace、debug、info、warning 和 error。
显然，trace 级别的消息只是高速发送的垃圾邮件。我想查看没有 trace 级别日志的所有消息。
所以我这样做了：
cat test.log | grep -v "trace"
效果很好。
现在我想根据某个关键字 keyword1 过滤剩余的消息。
所以我这样做了：
cat test.log | grep -v "trace" | grep "keyword1"
效果很好。
现在我想连续获得相同的输出，我想用 tail -f 替换 cat 。
tail -f test.log | grep -v "trace" | grep "keyword1"
但这是行不通的。我根本没有任何输出。
我做错了什么？我怎样才能得到我想要的过滤“尾部和尾部”？跟随'输出。
感谢您的帮助。
（顺便说一句，我正在使用 cygwin...如果这有什么关系的话）
I have a file test.log. Very big log file. It has different levels of logging. For eg, trace, debug, info, warning and error.
Obviously trace level messages are just spamming at high speeds. I wanted to see all the messages without trace level logs.
So I did this:
cat test.log | grep -v "trace"
Works good.
Now I want to filter the remaining messages based on a certain keyword keyword1.
So I did this:
cat test.log | grep -v "trace" | grep "keyword1"
Works good.
Now I want to get that same output on a continual basis, I thought of replacing cat with tail -f.
tail -f test.log | grep -v "trace" | grep "keyword1"
But this does not work. I get no output at all.
What am I doing wrong? And how can I get my desired filtered 'tail & follow' output.
Thanks for the help.
(btw, I am using cygwin... if that matters in any way)
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您遇到了缓冲问题：出于性能原因，
grep将在其缓冲区中保留相当多的输出，并一次性输出整个块。这意味着当从输入中读取一行时，一旦读取（并允许通过）更多行，grep 就会将其发送到 stdout - 这在处理日志时可能需要相当长的时间使用tail -f读入的文件。许多 grep 变体都可以切换到打开行缓冲模式，该模式将单独输出每一行 - 会造成一些性能损失。例如
GNU grep有一个--line-buffered选项来达到这个效果。只需将该选项（或适合您的
grep版本的选项）添加到所有grep调用中，只要将匹配的类似内容添加到日志中，您就会看到一些输出文件。You are encountering buffering issues: for performance reasons
grepwill keep quite a bit of output in its buffer and will output the whole chunk in one go. That means that when a line is read from the input,grepwill send it to stdout once it has read (and let through) even more lines - which can be quite some time later when dealing with a log file that is being read-in usingtail -f.Many
grepvariants have a switch to turn-on line-buffered mode, which will output each line on its own - with some performance loss. For exampleGNU grephas a--line-bufferedoption to achieve this effect.Just add that option (or the appropriate one for your version of
grep) to all yourgrepinvocations and you see some output as soon as a matching like is added to the log file.您的代码工作正常，您只是遇到缓冲延迟。因此，您将看到很长一段时间没有任何内容，然后是短暂的大量文本爆发，然后是另一次等待。阅读 http://perl.plover.com/FAQs/Buffering.html 获取解释正在发生的事情。
Your code is working fine, you're just encountering buffering delays. So you will see a long period of nothing, followed by a short burst of lots of text, followed by another wait. Read http://perl.plover.com/FAQs/Buffering.html for an explanation of what is going on.
tail -f跟随文件的“新传入行”。周期性输出永远不会到达管道grep命令（至少不会，直到tail终止）。要定期“跟踪”这些日志文件中的更改，您可能需要使用
watch：这将每秒 (
-n 1) 更新日志文件的最后 20 行日志档案。tail -ffollows the "new incoming lines" of a file. The periodic output will never reach the pipedgrepcommands (at least not, untiltailis terminated).To periodically "follow" changes in those log files, you might want to use
watchinstead:This'll update every second (
-n 1) the last 20 lines of the log file.