NAME
tail — deliver the last part of a file
SYNOPSIS
tail
[-f]
[-b
number]
[file]
tail
[-f]
[-c
number]
[file]
tail
[-f]
[-n
number]
[file]
Obsolescent:
tail
[±[number]][l|b
|c]
[-f]
[file]
DESCRIPTION
tail
copies the named
file
to the standard output beginning at a designated place.
If no
file
is named, standard input is used.
Command Forms
tail
can be used in three forms as indicated above:
- tail -b number...
Copy file starting at
number
blocks from end or beginning of file.
- tail -c number...
Copy file starting at
number
bytes from end or beginning of file.
- tail -n number...
- tail number...
Copy file starting at
number
lines from end or beginning of file.
tail
with no options specified is equivalent to
tail -n 10....
Options and Command-Line Arguments
tail
recognizes the following options and command-line arguments:
- -f
Follow option.
If the input file is a regular file or if
file
specifies a
FIFO,
do not terminate
after the last line of the input file has been copied,
but read and copy further bytes from the input file
when they become available
(tail
enters an endless loop wherein it sleeps for one second
then attempts to read and copy further records from the input file).
This is useful when monitoring text
being written to a file by another process.
If no
file
argument is specified and the input is a pipe
(FIFO),
the
-f
option is ignored.
- number
Decimal integer indicating quantity of output to be copied,
measured in units specified by accompanying option.
If
number
is preceded by a
+
character, copy operation starts
number
units from beginning of file.
If
number
is preceded by a
-
character or the option name,
copy operation starts
number
units from end of file.
If
number
is not preceded by a
b,
c,
or
n
option,
-n
is assumed.
If both the option and
number
are not specified,
-n 10
is assumed.
- -b number
Copy file beginning
number
512-byte blocks from end or beginning of file.
If
number
is not specified,
-b 10
is assumed.
See
number
description above.
- -c number
Copy file beginning
number
bytes from end or beginning of file.
If
number
is not specified,
-c 10
is assumed.
See
number
description above.
- -n number
Copy file beginning
number
lines from end or beginning of file.
If
number
is not specified,
-n 10
is assumed.
See
number
description above.
- file
Name of file to be copied.
If not specified, the standard input is used.
If the
-c
option is specified, the input file can contain arbitrary data.
Otherwise, the input file should be a text file.
Obsolescent Form
In the obsolescent form,
option letters can be concatenated after the
number
argument
to select blocks, bytes, or lines.
If this syntax is used,
±number
must be the first argument given.
If
number
is not specified, -10 is assumed.
This version is provided for backward compatibility only.
The forms discussed previously are recommended for portability.
EXTERNAL INFLUENCES
Environment Variables
LC_CTYPE
determines the locale for the interpretation of sequences of bytes of text
data as characters (e.g., single- versus multibyte characters in arguments
and input files).
LC_MESSAGES
determines the language in which messages are displayed.
If
LC_CTYPE
or
LC_MESSAGES
is not specified in the environment or is set to
the empty string, the value of
LANG
is used as a default for each
unspecified or empty variable.
If
LANG
is not specified or is set to the empty string, a default of "C" (see
lang(5))
is used instead of
LANG.
If any internationalization variable contains an invalid setting,
tail
behaves as if all internationalization variables are set to "C".
See
environ(5).
International Code Set Support
Single- and multi-byte character code sets are supported.
However, the
b
and
c
options can break multi-byte characters and should be used with caution
in a multi-byte locale environment.
EXAMPLES
Print the last three lines in file
file1
to the standard output, and leave
tail
in ``follow'' mode:
tail -fn 3 file1
tail -3 -f file1
Print the last 15 bytes of file
logfile
followed by any lines that are appended to
logfile
after
tail
is initiated until it is killed:
tail -fc15 logfile
tail -f -c 15 logfile
Three ways to print an entire file:
tail -b +1 file
tail -c +1 file
tail -n +1 file
WARNINGS
Various kinds of anomalous behavior may occur
with character special files.
For piped output,
tail
is limited in its output
and depends on process limits.
STANDARDS CONFORMANCE
tail: SVID2, SVID3, XPG2, XPG3, XPG4, POSIX.2
Printable version
