Combine tail -f with grep?

Question

Hi I wanna keep looking at a log file, but I also don't wanna see irrelevant stuff, I'm only interested in anything with "foobar" in it.

So if I was tailing the file I would do

 tail file | grep "foobar"

Now that I'm adding the -f option, is there a way to somehow only show the stuff that I want? using grep or other technique?

Solution

You almost wrote the answer, which is :

tail -f file.log | grep "foobar"

That's it.

Comments

[uSlackr]

It appears your answer is already written here: stackoverflow.com/questions/5427483/…

[JdeBP]

It appears that xyr answer is in the question.

[user893730]

Woah, you are right, I think I didn't expect this to work, I still don't, isn't piping supposed to happen when a command has finished execution? I guess this shows that it's not, it happens every time there an output, right?

[sparrow]

No it will launch the two programs in parallel, and the second one (grep) will exit as soon as tail's STDOUT closes. That's the whole point of pipes, data streaming :)

[ghoti]

When grep is the last line in the pipe, its output is line buffered, so you see the filtered output of tail -f live, rather than delayed. Note that if you were to use multiple grep commands, any whose output was piped would need a --line-buffered option (assuming GNU or BSD grep) in order to keep this behaviour.