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

This one command workes for me (Suse):

mail-srv:/var/log # tail -f /var/log/mail.info |grep --line-buffered LOGIN  >> logins_to_mail

collecting logins to mail service