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 <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` but it seems that `grep` can only be executed once `tail` finishes, that is to say never.

Answer 1

Use awk instead of grep since awk operates on the stream as it happens, e.g.:

$ tail -f wifi.log | awk '/kernel/{print $0}'

Fri May 3 21:29:21.352 <kernel> installGTK: setting cipher key (flags = 0x0)

Fri May 3 21:29:21.352 <kernel> GTK-RSC:

Fri May 3 21:29:21.352 <kernel> GTK:

Fri May 3 21:29:21.352 <kernel> installGTK: GTK installed

versus (no awk!)

$ tail -f wifi.log

Fri May 3 21:29:21.352 installGTK: setting cipher key (flags = 0x0)

Fri May 3 21:29:21.352 GTK-RSC:

Fri May 3 21:29:21.352 [00000000] 00 00 00 00 00 00

Fri May 3 21:29:21.352 GTK:

Fri May 3 21:29:21.352 [00000000] AE 5A D0 51 7F F6 5A 52 D6 DC B1 E7 E5 CD 73 9A

Fri May 3 21:29:21.352 installGTK: GTK installed