TAIL(1) General Commands Manual TAIL(1)NAME
tail - deliver the last part of a file
SYNOPSIS
tail [ +-number[lbc][rf] ] [ file ]
tail [ -fr ] [ -n nlines ] [ -c ncharacters ] [ file ]
DESCRIPTION
Tail copies the named file to the standard output beginning at a designated place. If no file is named, the standard input is copied.
Copying begins at position +number measured from the beginning, or -number from the end of the input. Number is counted in lines, 1K
blocks or characters, according to the appended flag or Default is -10l (ten ell).
The further flag causes tail to print lines from the end of the file in reverse order; (follow) causes tail, after printing to the end, to
keep watch and print further data as it appears.
The second syntax is that promulgated by POSIX, where the numbers rather than the options are signed.
EXAMPLES
tail file
Print the last 10 lines of a file.
tail +0f file
Print a file, and continue to watch data accumulate as it grows.
sed 10q file
Print the first 10 lines of a file.
SOURCE
/sys/src/cmd/tail.c
BUGS
Tails relative to the end of the file are treasured up in a buffer, and thus are limited in length.
According to custom, option +number counts lines from 1, and counts blocks and characters from 0.
TAIL(1)
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TAIL(1) BSD General Commands Manual TAIL(1)NAME
tail -- display the last part of a file
SYNOPSIS
tail [-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 to not 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 the standard input is a pipe, but not if it is a FIFO.
-F The -F option implies the -f option, but tail will also check to see if the file being followed has been renamed or rotated. The
file is closed and reopened when tail detects that the filename being read from has a new inode number. The -F option is ignored if
reading from standard input rather than a file.
-n 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.
DIAGNOSTICS
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 -F, -b and -r
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 PWB UNIX.
BSD June 6, 1993 BSD