NAME
tail —
display the last part of a
file
SYNOPSIS
tail |
-qv [-f |
-F | -r]
[-b number |
-c number | -n
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
- The -f option causes
tail not to stop when end of file is reached, but rather
to wait for additional data to be appended to the input. The
-f option is ignored if there are no file arguments and
the standard input is a pipe or a FIFO.
-
-
- -F
- The -F option is the same as the
-f option, except that every five seconds
tail will check to see if the file named on the command
line has been shortened or moved (it is considered moved if the inode or
device number changes) and, if so, it will close the current file, open
the filename given, print out the entire contents, and continue to wait
for more data to be appended. This option is used to follow log files
though rotation by
newsyslog(8) or similar
programs.
-
-
- -n
number
- The location is number lines.
-
-
- -q
- Do not prepend a header for each file, even if multiple
files are specified.
-
-
- -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.
-
-
- -v
- Prepend each file with a header.
If more than a single file is specified, or the
-v option is
used, each file is preceded by a header consisting of the string “==>
XXX ≤=” where “XXX” is the name of the file. The
-q flag disables the printing of the header in all cases.
EXIT STATUS
The
tail utility exits 0 on success, and >0 if an
error occurs.
SEE ALSO
cat(1),
head(1),
sed(1)
STANDARDS
The
tail utility is expected to be a superset of the
IEEE Std 1003.2-1992 (“POSIX.2”)
specification. In particular, the
-b,
-r
and
-F options are extensions to that standard.
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.
BUGS
When using the
-F option,
tail will not
detect a file truncation if, between the truncation and the next check of the
file size, data written to the file make it larger than the last known file
size.