c2895f1934
Add four simple examples showing the use of -c, -r and -s Approved by: manpages (bcr@) Differential Revision: https://reviews.freebsd.org/D25774
201 lines
5.0 KiB
Groff
201 lines
5.0 KiB
Groff
.\"
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.\" Copyright (c) 2000 Sheldon Hearn <sheldonh@FreeBSD.org>.
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.\" All rights reserved.
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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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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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.\" $FreeBSD$
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.\"
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.Dd July 27, 2020
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.Dt TRUNCATE 1
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.Os
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.Sh NAME
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.Nm truncate
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.Nd truncate or extend the length of files
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.Sh SYNOPSIS
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.Nm
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.Op Fl c
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.Bk -words
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.Fl s Xo
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.Sm off
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.Op Cm + | - | % | /
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.Ar size
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.Op Cm K | k | M | m | G | g | T | t
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.Sm on
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.Xc
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.Ek
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.Ar
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.Nm
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.Op Fl c
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.Bk -words
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.Fl r Ar rfile
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.Ek
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.Ar
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.Sh DESCRIPTION
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The
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.Nm
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utility adjusts the length of each regular file given on the command-line.
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.Pp
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The following options are available:
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.Bl -tag -width indent
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.It Fl c
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Do not create files if they do not exist.
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The
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.Nm
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utility does not treat this as an error.
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No error messages are displayed
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and the exit value is not affected.
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.It Fl r Ar rfile
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Truncate or extend files to the length of the file
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.Ar rfile .
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.It Fl s Xo
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.Sm off
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.Op Cm + | - | % | /
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.Ar size
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.Op Cm K | k | M | m | G | g | T | t
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.Sm on
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.Xc
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If the
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.Ar size
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argument is preceded by a plus sign
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.Pq Cm + ,
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files will be extended by this number of bytes.
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If the
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.Ar size
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argument is preceded by a dash
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.Pq Cm - ,
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file lengths will be reduced by no more than this number of bytes,
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to a minimum length of zero bytes.
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If the
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.Ar size
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argument is preceded by a percent sign
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.Pq Cm % ,
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files will be round up to a multiple of this number of bytes.
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If the
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.Ar size
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argument is preceded by a slash sign
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.Pq Cm / ,
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files will be round down to a multiple of this number of bytes,
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to a minimum length of zero bytes.
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Otherwise, the
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.Ar size
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argument specifies an absolute length to which all files
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should be extended or reduced as appropriate.
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.Pp
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The
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.Ar size
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argument may be suffixed with one of
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.Cm K ,
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.Cm M ,
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.Cm G
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or
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.Cm T
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(either upper or lower case) to indicate a multiple of
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Kilobytes, Megabytes, Gigabytes or Terabytes
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respectively.
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.El
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.Pp
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Exactly one of the
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.Fl r
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and
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.Fl s
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options must be specified.
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.Pp
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If a file is made smaller, its extra data is lost.
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If a file is made larger,
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it will be extended as if by writing bytes with the value zero.
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If the file does not exist,
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it is created unless the
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.Fl c
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option is specified.
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.Pp
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Note that,
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while truncating a file causes space on disk to be freed,
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extending a file does not cause space to be allocated.
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To extend a file and actually allocate the space,
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it is necessary to explicitly write data to it,
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using (for example) the shell's
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.Ql >>
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redirection syntax, or
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.Xr dd 1 .
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.Sh EXIT STATUS
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.Ex -std
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If the operation fails for an argument,
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.Nm
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will issue a diagnostic
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and continue processing the remaining arguments.
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.Sh EXAMPLES
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Adjust the size of the file
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.Pa test_file
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to 10 Megabytes but do not create it if it does not exist:
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.Bd -literal -offset indent
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truncate -c -s +10M test_file
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.Ed
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.Pp
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Same as above but create the file if it does not exist:
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.Bd -literal -offset indent
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truncate -s +10M test_file
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ls -l test_file
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-rw-r--r-- 1 root wheel 10485760 Jul 22 18:48 test_file
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.Ed
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.Pp
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Adjust the size of
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.Pa test_file
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to the size of the kernel and create another file
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.Pa test_file2
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with the same size:
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.Bd -literal -offset indent
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truncate -r /boot/kernel/kernel test_file test_file2
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ls -l /boot/kernel/kernel test_file*
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-r-xr-xr-x 1 root wheel 31352552 May 15 14:18 /boot/kernel/kernel*
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-rw-r--r-- 1 root wheel 31352552 Jul 22 19:15 test_file
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-rw-r--r-- 1 root wheel 31352552 Jul 22 19:15 test_file2
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.Ed
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.Pp
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Downsize
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.Pa test_file
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in 5 Megabytes:
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.Bd -literal -offset indent
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# truncate -s -5M test_file
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ls -l test_file*
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-rw-r--r-- 1 root wheel 26109672 Jul 22 19:17 test_file
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-rw-r--r-- 1 root wheel 31352552 Jul 22 19:15 test_file2
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.Ed
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.Sh SEE ALSO
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.Xr dd 1 ,
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.Xr touch 1 ,
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.Xr truncate 2
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.Sh STANDARDS
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The
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.Nm
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utility conforms to no known standards.
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.Sh HISTORY
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The
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.Nm
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utility first appeared in
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.Fx 4.2 .
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.Sh AUTHORS
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The
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.Nm
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utility was written by
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.An Sheldon Hearn Aq Mt sheldonh@starjuice.net .
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