Question : read lines from a tail(ed) -f file.

I have a log file that I need to monitor for certain events.  I want the event I am looking for to be captured so I can modify the line and save to a new file.  This will eventually run as a service.  It appears there is a breakdown in the redirection to the read line command.  This is what I have:
tail -f "logfile_name" | grep "eventName" | while read line
do
echo $line
done
To test I tail -f | grep "eventName the logfile and then run this script in a seperate shell.  The output should be the same, but sometimes it gives me output and sometimes not.

Answer : read lines from a tail(ed) -f file.

Is one shorter?
it's probably because the pipes are buffered
it may or may not help to use something like
tail -f logfile_name | perl -ne '$|=1; print if /eventName/' | while read line