如何“grep"连续流? [英] How to 'grep' a continuous stream?

问题描述

可以在连续流上使用 grep 吗?

Is that possible to use grep on a continuous stream?

我的意思是一种 tail -f 命令，但是在输出上带有 grep 以便只保留我感兴趣的行.

What I mean is sort of a tail -f <file> command, but with grep on the output in order to keep only the lines that interest me.

我试过 tail -f ;|grep 模式 但似乎grep 只能在tail 完成后执行，也就是说从不.

I've tried tail -f <file> | grep pattern but it seems that grep can only be executed once tail finishes, that is to say never.

推荐答案

在使用 BSD grep (FreeBSD, Mac OS X etc.) 时打开 grep 的行缓冲模式

Turn on grep's line buffering mode when using BSD grep (FreeBSD, Mac OS X etc.)

tail -f file | grep --line-buffered my_pattern

它看起来像不久前 --line-buffered 对 GNU grep(几乎在任何 Linux 上都使用过)无关紧要，因为它默认刷新(YMMV 用于其他类 Unix，例如SmartOS、AIX 或 QNX).但是，截至 2020 年 11 月，需要 --line-buffered(至少在 openSUSE 中使用 GNU grep 3.5，但根据下面的评论似乎通常需要).

It looks like a while ago --line-buffered didn't matter for GNU grep (used on pretty much any Linux) as it flushed by default (YMMV for other Unix-likes such as SmartOS, AIX or QNX). However, as of November 2020, --line-buffered is needed (at least with GNU grep 3.5 in openSUSE, but it seems generally needed based on comments below).

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