Most of us have used the tail command to view the last
ten lines of a file.
The tail command has a -f option that may be
used to watch a file grow dynamically.
Consider a process that periodically appends text to a file (perhaps to log
its progress).
tail -f filename displays the last ten
lines of the file, then continues to display new lines as they are appended.
The -f option causes tail to never
terminate; you'll not see your shell prompt again until you kill the process
with ^C.
Your clever systems manager frequently uses this to observe log files. Did
an X-terminal really boot properly, receiving its correct configuration file?
Starting tail -f on the system's daemon log file, then
booting the X-terminal reveals all the details of the boot process, as they
occur.
A useful mnemonic might be to think of it as the "-forever" option.
Try man tail if you think of it. The -r
option is interesting, too!