TAIL(1) | General Commands Manual | TAIL(1) |
tail
—
tail |
-qv [-f |
-F | -r ]
[-b number |
-c number |
-n number]
[file ...] |
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-c
number-f
-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
-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-q
-r
-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
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.
tail
utility exits 0 on success,
and >0 if an error occurs.
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.
tail
command appeared in
Version 7 AT&T UNIX.
-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.
October 1, 2017 | NetBSD 9.4 |