How to use the watch command to update a terminal every 2 seconds with an updating file.

I am using this command to search the Internet for open ports on port 80 with nmap.

sudo nmap -sS -iR 0 -p 80 -oG nmap.grepable

Then I use this command in another terminal tab to view the updating file. This will be updated every two seconds with new file content.

watch cat nmap.grepable

This is a good way to monitor files for any changes.

This is another good way. This command will constantly monitor the /var/log/dmesg file for any new kernel messages.

watch tail -n 10 /var/log/dmesg

This command will watch for new kernel messages.

watch tail /var/log/kern.log

The watch command is a very useful tool to run in a spare xterm to monitor your logfiles. Give these tricks a try and see how useful they really are.