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 makestail
more useful for watching log files that may get rotated. The-f
option is ignored if the standard input is a pipe, but not if it is 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 a single file is specified, each file is preceded by a header consisting of the string “==> XXX <==” where “XXX” is the name of the file.
EXIT STATUS
The tail
utility exits 0 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
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 appeared in
Version 7 AT&T UNIX.