How to 'grep' a continuous stream?

Is that possible to use grep on a continuous stream?

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.

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

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

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

You don't need to do this for GNU grep (used on pretty much any Linux) as it will flush by default (YMMV for other Unix-likes such as SmartOS, AIX or QNX).

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

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

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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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