This tutorial should work properly on all Unix based OSes.
If you need to keep an eye on a command whose output is changing, use the watch
For example, to keep an eye on your load average:
$ watch ‘cat /proc/loadavg’
Every two seconds, watch runs the cat command again. Use Ctrl+c to quit. To
change the refresh rate to 10 seconds, type the following:
$ watch -n 10 ‘ls -l’
To highlight the difference between screen updates, type:
$ watch -d ‘ls -l’
Type Ctrl+c to exit the watch command.
You can use the watch command to watch the size of a file. For example, to watch a large ISO file named mydownload.iso as it downloads, use the following command:
$ watch ‘ls –l mydownload.iso’
To watch the contents of a plain text file grow over time, you can use the tail com-
mand. For example, you can watch as messages are added to the /var/log/messages
file as follows:
$ tail -f /var/log/messages
Pressing Ctrl+c will exit from the tail command.