[unix-history] / 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.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"	@(#)tail.1	6.8 (Berkeley) 2/12/92
.\"
.Dd February 12, 1992
.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 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 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 location 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 b
and
.Fl r
options are extensions to that standard.
.Pp
The historic command line syntax of
.Nm tail
is supported by this implementation.
The only difference between this implementation and historic versions
of
.Nm tail ,
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 tail
command appeared in
.At v7 .
Commit	Line	Data
78ed81a3	1	.\" Copyright (c) 1980, 1990, 1991 Regents of the University of California.
	2	.\" All rights reserved.
	3	.\"
	4	.\" This code is derived from software contributed to Berkeley by
	5	.\" the Institute of Electrical and Electronics Engineers, Inc.
	6	.\"
	7	.\" Redistribution and use in source and binary forms, with or without
	8	.\" modification, are permitted provided that the following conditions
	9	.\" are met:
	10	.\" 1. Redistributions of source code must retain the above copyright
	11	.\" notice, this list of conditions and the following disclaimer.
	12	.\" 2. Redistributions in binary form must reproduce the above copyright
	13	.\" notice, this list of conditions and the following disclaimer in the
	14	.\" documentation and/or other materials provided with the distribution.
	15	.\" 3. All advertising materials mentioning features or use of this software
	16	.\" must display the following acknowledgement:
	17	.\" This product includes software developed by the University of
	18	.\" California, Berkeley and its contributors.
	19	.\" 4. Neither the name of the University nor the names of its contributors
	20	.\" may be used to endorse or promote products derived from this software
	21	.\" without specific prior written permission.
	22	.\"
	23	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	24	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	25	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	26	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	27	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	28	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	29	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	30	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	31	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	32	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	33	.\" SUCH DAMAGE.
	34	.\"
	35	.\" @(#)tail.1 6.8 (Berkeley) 2/12/92
	36	.\"
	37	.Dd February 12, 1992
	38	.Dt TAIL 1
	39	.Os BSD 4
	40	.Sh NAME
	41	.Nm tail
	42	.Nd display the last part of a file
	43	.Sh SYNOPSIS
	44	.Nm tail
	45	.Op Fl f Li \| Fl r
	46	.Oo
	47	.Fl b Ar number \|
	48	.Fl c Ar number \|
	49	.Fl n Ar number
	50	.Oc
	51	.Op Ar file
	52	.Sh DESCRIPTION
	53	The
	54	.Nm tail
	55	utility displays the contents of
	56	.Ar file
	57	or, by default, its standard input, to the standard output.
	58	.Pp
	59	The display begins at a byte, line or 512-byte block location in the
	60	input.
	61	Numbers having a leading plus (``+'') sign are relative to the beginning
	62	of the input, for example,
	63	.Dq -c +2
	64	starts the display at the second
65	byte of the input.
66	Numbers having a leading minus (``-'') sign or no explicit sign are
67	relative to the end of the input, for example,
68	.Dq -n 2
69	displays the last two lines of the input.
70	The default starting location is
71	.Dq -n 10 ,
72	or the last 10 lines of the input.
73	.Pp
74	The options are as follows:
75	.Bl -tag -width Ds
76	.It Fl b Ar number
77	The location is
78	.Ar number
15637ed4	79	512-byte blocks.
78ed81a3	80	.It Fl c Ar number
	81	The location is
	82	.Ar number
	83	bytes.
	84	.It Fl f
	85	The
	86	.Fl f
	87	option causes
	88	.Nm tail
	89	to not stop when end of file is reached, but rather to wait for additional
	90	data to be appended to the input.
	91	The
	92	.Fl f
	93	option is ignored on pipes but not on FIFO's.
	94	.It Fl n Ar number
	95	The location is
	96	.Ar number
	97	lines.
	98	.It Fl r
	99	The
	100	.Fl r
	101	option causes the input to be displayed in reverse order, by line.
	102	Additionally, this option changes the meaning of the
	103	.Fl b ,
	104	.Fl c
	105	and
	106	.Fl n
	107	options.
	108	When the
	109	.Fl r
	110	option is specified, these options specify the number of bytes, lines
	111	or 512-byte blocks to display, instead of the bytes, lines or blocks
	112	from the beginning or end of the input from which to begin the display.
	113	The default for the
	114	.Fl r
	115	option is to display all of the input.
	116	.El
	117	.Pp
	118	The
	119	.Nm tail
	120	utility exits 0 on success, and >0 if an error occurs.
	121	.Sh SEE ALSO
	122	.Xr cat 1 ,
	123	.Xr head 1 ,
	124	.Xr sed 1
	125	.Sh STANDARDS
	126	The
	127	.Nm tail
	128	utility is expected to be a superset of the POSIX 1003.2
	129	specification.
	130	In particular, the
	131	.Fl b
	132	and
	133	.Fl r
	134	options are extensions to that standard.
	135	.Pp
	136	The historic command line syntax of
	137	.Nm tail
	138	is supported by this implementation.
	139	The only difference between this implementation and historic versions
	140	of
	141	.Nm tail ,
	142	once the command line syntax translation has been done, is that the
	143	.Fl b ,
144	.Fl c
145	and
146	.Fl n
147	options modify the
148	.Fl r
149	option, i.e. ``-r -c 4'' displays the last 4 characters of the last line
150	of the input, while the historic tail (using the historic syntax ``-4cr'')
151	would ignore the
152	.Fl c
153	option and display the last 4 lines of the input.
154	.Sh HISTORY
155	A
156	.Nm tail
157	command appeared in
158	.At v7 .