tail —
display the last part of a file
tail |
[ -f |
-r
]
[-b
number |
-c
number |
-n
number |
-
number
]
[file ... ] |
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
<==
The
tail utility exits 0 on success,
and >0 if an error occurs.
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
cat(1),
head(1),
sed(1)
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.
A
tail command appeared in
Version 7 AT&T UNIX.
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