tail [options] [files]

Print the last 10 lines of each named file on standard output. Print from standard input with no filename or with -. If more than one
file is specified, the output includes a header at the beginning of each file:
==> filename <==
For options that take the number of bytes or lines as an argument, you can prepend a plus sign (+) to num to begin printing with the
numth item. These options can also specify a block size:

b 512 bytes
K 1 kilobyte
M 1 megabyte
G 1 gigabyte

Options
-c num, --bytes num
Print the last num bytes.
-f, --follow[=name|descriptor]
Don’t quit at the end of file; “follow” file as it grows and end when the user presses Ctrl-C. Following by file descriptor is the default, so -f, --follow, and --follow=descriptor are equivalent. Use --follow=name to track the actual name of a file even if the file is renamed, as with a rotated logfile.
-F Identical to --follow=name --retry.
--help
Print a help message and exit.
-n num, --lines=num
Print the last num lines.
--max-unchanged-stats=num
Used with --follow=name to reopen a file whose size hasn’t changed after num iterations (default 5), to see if it has been unlinked or renamed (as with rotated logfiles).
--pid=pid
Used with -f to end when process ID pid dies.
-q, --quiet, --silent
Suppress filename headers.

--retry
Keep trying to open a file even if it isn’t accessible when tail starts or if it becomes inaccessible later. Useful with --follow=name.
-s sec, --sleep-interval=sec
With -f, sleep approximately sec seconds between iterations. Default is 1 second.
-v, --verbose
With multiple files, always output the filename headers.
--version
Print version information and then exit.

Examples:

grep '\.Ah' file | tail -20         Show the last 20 lines containing instances of .Ah:

tail -f /var/log/messages         Monitor messages in a log file