[ale] Command pipes and buffering

Kevin Krumwiede krum at smyrnacable.net
Tue Apr 23 17:06:57 EDT 2002


My iptables logging rules put 'firewall' in the log message.  Just for
fun, I tried to watch for events using this command:

# tail -f -n 0 /var/log/kernel/warnings | grep firewall | cut -d' ' \
-f 3,10,17,18,19

It doesn't print anything until it has a bunch of lines to print. 
Curiously, if I leave out the '-f -n 0' argument to tail it works (but
it's useless), and if I don't pipe through cut it works.  If I just take
out the '-n 0' it doesn't work, even when the last few lines of the log
contain iptables messages.

Is there any way to control this?

Krum


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