Where can I get free tips about Linux shell script programming?

Can a shell script read and process a file which is continuously being written to (like the --follow option in tail)?

Basically I would like to read a log file and when I find a certain string, generate a firewall entry to block this IP. The script needs to continuously read this file, not a one time shot.

Hmmm.... that's an interesting question. Let's see.... I think I would use some sort of loop where I'd use 'tail -f' on the relevant file, then sleep some period of time, then check the file again for updates. If you keep track of the lines in the file, you could always use that as a change marker (though you'd sometimes be off an iteration because of the file changing between the 'wc' call and the actual test of the returned value).

But it should be quite doable!

What I did for now, until I think of (or find) a better way:

tail -f /var/log/mail/info writes into a fifo
block_ips reads from the same fifo

Where block_ips is the shell script that processes the log file.

Hi Buddy...

You can find a lots of unix tips & tricks at www.unixground.blogspot.com

Regards,
Sanju