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\"      @(#)tail.1      8.1 (Berkeley) 6/6/93
\"
Dd October 1, 2017
Dt TAIL 1
Os
Sh NAME
Nm tail
Nd display the last part of a file
Sh SYNOPSIS
Nm
Fl qv
Oo
Fl f |
Fl F |
Fl r
Oc
Oo
Fl b Ar number |
Fl c Ar number |
Fl n Ar number
Oc
Op Ar file ...
Sh DESCRIPTION
The
Nm
utility displays the contents of
Ar file
or, by default, its standard input, to the standard output.
Pp
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,
Dq -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,
Dq -n 2
displays the last two lines of the input.
The default starting location is
Dq -n 10 ,
or the last 10 lines of the input.
Pp
The options are as follows:
Bl -tag -width Ds
It Fl b Ar number
The location is
Ar number
512-byte blocks.
It Fl c Ar number
The location is
Ar number
bytes.
It Fl f
The
Fl f
option causes
Nm
not to stop when end of file is reached, but rather to wait for additional
data to be appended to the input.
The
Fl f
option is ignored if there are no file arguments and the standard
input is a pipe or a FIFO.
It Fl F
The
Fl F
option is the same as the
Fl f
option, except that every five seconds
Nm
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
Xr newsyslog 8
or similar programs.
It Fl n Ar number
The location is
Ar number
lines.
It Fl q
Do not prepend a header for each file, even if multiple files
are specified.
It Fl r
The
Fl r
option causes the input to be displayed in reverse order, by line.
Additionally, this option changes the meaning of the
Fl b ,
Fl c
and
Fl n
options.
When the
Fl 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
Fl r
option is to display all of the input.
It Fl v
Prepend each file with a header.
El
Pp
If more than a single file is specified, or the
Fl v
option is used, each file is preceded by a
header consisting of the string
Dq ==> XXX <==
where
Dq XXX
is the name of the file.
The
Fl q
flag disables the printing of the header in all cases.
Sh EXIT STATUS
Ex -std tail
Sh SEE ALSO
Xr cat 1 ,
Xr head 1 ,
Xr sed 1
Sh STANDARDS
The
Nm
utility is expected to be a superset of the
St -p1003.2-92
specification.
In particular, the
Fl b ,
Fl r
and
Fl F
options are extensions to that standard.
Pp
The historic command line syntax of
Nm
is supported by this implementation.
The only difference between this implementation and historic versions
of
Nm ,
once the command line syntax translation has been done, is that the
Fl b ,
Fl c
and
Fl n
options modify the
Fl 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
Fl c
option and display the last 4 lines of the input.
Sh HISTORY
A
Nm
command appeared in
At v7 .
Sh BUGS
When using the
Fl F
option,
Nm
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.

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