TAIL(1) - General Commands Manual #

TAIL(1) - General Commands Manual

NAME #

tail - display the last part of a file

SYNOPSIS #

tail [-f | -r] [-b number | -c number | -n number | -‌number] [file …]

DESCRIPTION #

The tail utility displays the contents of file or, by default, its standard input, to the standard output.

The display begins at a byte, line, or 512-byte block location in the input. Numbers having a leading plus (’+’) sign are relative to the beginning of the input, for example, -c +2 starts the display at the second byte of the input. Numbers having a leading minus (’-’) sign or no explicit sign are relative to the end of the input, for example, -n 2 displays the last two lines of the input. The default starting location is -n 10, or the last 10 lines of the input.

The options are as follows:

-b number

The location is
*number*
512-byte blocks.

-c number

The location is
*number*
bytes.

-f

Do not stop when end-of-file is reached; instead, wait for additional
data to be appended to the input.
If the file is replaced (i.e., the inode number changes),
**tail**
will reopen the file and continue.
If the file is truncated,
**tail**
will reset its position to the beginning.
This makes
**tail**
more useful for watching log files that may get rotated.
The
**-f**
option is ignored if there are no
*file*
arguments and the standard input is a pipe or a FIFO.

-n number | **-**number

The location is
*number*
lines.

-r

The
**-r**
option causes the input to be displayed in reverse order, by line.
Additionally, this option changes the meaning of the
**-b**,
**-c**,
and
**-n**
options.
When the
**-r**
option is specified, these options specify the number of bytes, lines
or 512-byte blocks to display, instead of the bytes, lines, or blocks
from the beginning or end of the input from which to begin the display.
The default for the
**-r**
option is to display all of the input.

If more than one file is specified, tail precedes the output of each file with the following, in order to distinguish files:

==> *file* <==

EXIT STATUS #

The tail utility exits0 on success, and>0 if an error occurs.

EXAMPLES #

To display the last 500 lines of the file foo:

$ tail -500 foo

Keep /var/log/messages open, displaying to the standard output anything appended to the file:

$ tail -f /var/log/messages

SEE ALSO #

cat(1), head(1), sed(1)

STANDARDS #

The tail utility is compliant with the IEEE Std 1003.1-2008 (“POSIX.1”) specification.

The flags [-br] are extensions to that specification.

The historic command line syntax of tail is supported by this implementation. The only difference between this implementation and historic versions of tail, once the command line syntax translation has been done, is that the -b, -c and -n options modify the -r option, i.e., -r -c 4 displays the last 4 characters of the last line of the input, while the historic tail (using the historic syntax -4cr) would ignore the -c option and display the last 4 lines of the input.

HISTORY #

A tail command first appeared outside of Bell Labs in PWB/UNIX 1.0.

OpenBSD 7.5 - August 3, 2022