new version from scratch; POSIX 1003.2 version

[unix-history] / usr / src / usr.bin / tail / tail.1

.\" Copyright (c) 1980, 1990, 1991 Regents of the University of California.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" the Institute of Electrical and Electronics Engineers, Inc.
.\"
.\" %sccs.include.redist.roff%
.\"
.\"	@(#)tail.1	6.7 (Berkeley) %G%
.\"
.Dd 
.Dt TAIL 1
.Os BSD 4
.Sh NAME
.Nm tail
.Nd display the last part of a file
.Sh SYNOPSIS
.Nm tail
.Op Fl f Li | Fl r
.Oo
.Fl b Ar number |
.Fl c Ar number |
.Fl n Ar number
.Oc
.Op Ar file
.Sh DESCRIPTION
The
.Nm tail
utility displays the contents of
.Ar file
or, by default, its standard input, to the standard output.
.Pp
The display begins at an offset from either the beginning or end
of the input.
Offsets may be specified in terms of bytes, lines or 512-byte blocks.
Numbers having a leading plus (``+'') sign are relative to the beginning
of the input.
Numbers having a leading minus (``-'') sign or no explicit sign are
relative to the end of the input.
All offsets are 1 based, i.e. ``-c +1'' skips a single byte of the
input.
The default offset is ``-n 10'', or 10 lines from the end of the
input.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl b Ar number
The offset is
.Ar number
512-byte blocks.
.It Fl c Ar number
The offset is
.Ar number
bytes.
.It Fl f
The
.Fl f
option causes
.Nm tail
to not 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 on pipes but not on FIFO's.
.It Fl n Ar number
The offset is
.Ar number
lines.
.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.
.El
.Pp
The
.Nm tail
utility exits 0 on success, and >0 if an error occurs.
.Sh SEE ALSO
.Xr cat 1 ,
.Xr head 1 ,
.Xr sed 1
.Sh STANDARDS
The
.Nm tail
utility is expected to be a superset of the POSIX 1003.2
specification.
In particular, the
.Fl r
option is an extension to that standard.
.Sh HISTORY
A
.Nm tail
command appeared in
.At v7 .