How to 'grep' a continuous stream?

Question

Is that possible to use grep on a continuous stream?

What I mean is sort of a tail -f command, but with grep on t

Answer 1

sed would be a better choice (stream editor)

tail -n0 -f | sed -n '/search string/p'

and then if you wanted the tail command to exit once you found a particular string:

tail --pid=$(($BASHPID+1)) -n0 -f | sed -n '/search string/{p; q}'

Obviously a bashism: $BASHPID will be the process id of the tail command. The sed command is next after tail in the pipe, so the sed process id will be $BASHPID+1.