Frequently Asked Question

What is the difference between head, tail, and tail -f?

head prints the first lines of a file (10 by default; head -n 20 for 20). tail prints the last lines of a file (also 10 by default). Both are useful for peeking at the shape of a file without scrolling the terminal. head is typically used at the end of a pipeline to limit output to the top N results, as in sort -rn | head to grab the top ten.

tail -f (for follow) is the killer feature: it prints the last lines of the file and then keeps watching, printing each new line as it is appended. Running tail -f /var/log/syslog in one terminal window while you debug a service in another is a standard sysadmin posture, every error the service logs appears in real time. tail -F (capital F) is similar but copes with log rotation: if the file is replaced or truncated, it reopens the new file rather than silently watching the dead inode.