192 lines
5.2 KiB
Groff
192 lines
5.2 KiB
Groff
.\" $NetBSD: tail.1,v 1.14 2013/01/31 23:09:06 wiz Exp $
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.\"
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.\" Copyright (c) 1980, 1990, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" the Institute of Electrical and Electronics Engineers, Inc.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)tail.1 8.1 (Berkeley) 6/6/93
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.\"
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.Dd June 6, 1993
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.Dt TAIL 1
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.Os
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.Sh NAME
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.Nm tail
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.Nd display the last part of a file
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.Sh SYNOPSIS
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.Nm
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.Oo
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.Fl f |
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.Fl F |
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.Fl r
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.Oc
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.Oo
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.Fl b Ar number |
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.Fl c Ar number |
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.Fl n Ar number
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.Oc
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.Op Ar file ...
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.Sh DESCRIPTION
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The
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.Nm
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utility displays the contents of
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.Ar file
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or, by default, its standard input, to the standard output.
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.Pp
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The display begins at a byte, line or 512-byte block location in the
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input.
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Numbers having a leading plus (``+'') sign are relative to the beginning
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of the input, for example,
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.Dq -c +2
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starts the display at the second
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byte of the input.
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Numbers having a leading minus (``-'') sign or no explicit sign are
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relative to the end of the input, for example,
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.Dq -n 2
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displays the last two lines of the input.
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The default starting location is
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.Dq -n 10 ,
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or the last 10 lines of the input.
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.Pp
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The options are as follows:
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.Bl -tag -width Ds
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.It Fl b Ar number
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The location is
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.Ar number
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512-byte blocks.
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.It Fl c Ar number
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The location is
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.Ar number
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bytes.
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.It Fl f
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The
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.Fl f
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option causes
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.Nm
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to not stop when end of file is reached, but rather to wait for additional
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data to be appended to the input.
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The
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.Fl f
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option is ignored if the standard input is a pipe, but not if it is a FIFO.
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.It Fl F
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The
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.Fl F
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option is the same as the
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.Fl f
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option, except that every five seconds
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.Nm
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will check to see if the file named on the command line has been
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shortened or moved (it is considered moved if the inode or device
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number changes) and, if so, it will close
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the current file, open the filename given, print out the entire
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contents, and continue to wait for more data to be appended.
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This option is used to follow log files though rotation by
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.Xr newsyslog 8
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or similar programs.
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.It Fl n Ar number
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The location is
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.Ar number
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lines.
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.It Fl r
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The
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.Fl r
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option causes the input to be displayed in reverse order, by line.
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Additionally, this option changes the meaning of the
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.Fl b ,
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.Fl c
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and
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.Fl n
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options.
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When the
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.Fl r
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option is specified, these options specify the number of bytes, lines
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or 512-byte blocks to display, instead of the bytes, lines or blocks
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from the beginning or end of the input from which to begin the display.
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The default for the
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.Fl r
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option is to display all of the input.
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.El
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.Pp
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If more than a single file is specified, each file is preceded by a
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header consisting of the string
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.Dq ==\*[Gt] XXX \*[Le]=
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where
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.Dq XXX
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is the name of the file.
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.Pp
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The
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.Nm
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utility exits 0 on success, and \*[Gt]0 if an error occurs.
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.Sh SEE ALSO
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.Xr cat 1 ,
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.Xr head 1 ,
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.Xr sed 1
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.Sh STANDARDS
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The
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.Nm
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utility is expected to be a superset of the
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.St -p1003.2-92
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specification.
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In particular, the
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.Fl b ,
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.Fl r
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and
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.Fl F
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options are extensions to that standard.
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.Pp
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The historic command line syntax of
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.Nm
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is supported by this implementation.
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The only difference between this implementation and historic versions
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of
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.Nm ,
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once the command line syntax translation has been done, is that the
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.Fl b ,
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.Fl c
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and
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.Fl n
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options modify the
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.Fl r
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option, i.e., ``-r -c 4'' displays the last 4 characters of the last line
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of the input, while the historic tail (using the historic syntax ``-4cr'')
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would ignore the
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.Fl c
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option and display the last 4 lines of the input.
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.Sh HISTORY
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A
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.Nm
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command appeared in
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.At v7 .
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.Sh BUGS
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When using the
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.Fl F
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option,
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.Nm
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will not detect a file truncation if, between the truncation
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and the next check of the file size, data written to the file make
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it larger than the last known file size.
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