tail command examples

View the Constantly Updated Last Lines of a File or Files

tail -f
tail -f --pid=PID# terminates after PID dies.
The great thing about log files is that they constantly change as things happen on your system. The tail command shows you a snapshot of a file, and then deposits you back on the command line. Want to see the log file again? Then run tail again...and again...and again. Blech!
With the -f (or --follow) option, tail doesn't close. Instead, it shows you the last 10 lines of the file (or a different number if you add -n to the mix) as the file changes, giving you a way to watch all the changes to a log file as they happen. This is wonderfully useful if you're trying to figure out just what is happening to a system or program.
For instance, a web server's logs might look like this:
Note
In order to save space, I've removed the IP address, date, and time of the access.

$ tail -f /var/log/httpd/d20srd_org_log_20051201
"GET /srd/skills/bluff.htm HTTP/1.1"...
"GET /srd/skills/senseMotive.htm HTTP/1.1"...
"GET /srd/skills/concentration.htm HTTP/1.1"...
"GET /srd/classes/monk.htm HTTP/1.1"...
"GET /srd/skills/escapeArtist.htm HTTP/1.1"...