How to 'grep' a continuous stream? How to 'grep' a continuous stream? linux linux

How to 'grep' a continuous stream?


linux bash shell grep tail

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

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

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).

linux bash shell grep tail

I use the tail -f <file> | grep <pattern> all the time.

It will wait till grep flushes, not till it finishes (I'm using Ubuntu).

linux bash shell grep tail

I think that your problem is that grep uses some output buffering. Try 

tail -f file | stdbuf -o0 grep my_pattern

it will set output buffering mode of grep to unbuffered.

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