mirror of https://github.com/GnoConsortium/gno.git
209 lines
6.1 KiB
Groff
209 lines
6.1 KiB
Groff
.\" Copyright (c) 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. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. 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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.\" @(#)cksum.1 8.2 (Berkeley) 4/28/95
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.\" $Id: cksum.1,v 1.2 1998/02/15 00:25:44 gdr-ftp Exp $
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.\"
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.TH CKSUM 1 "December 1997" "GNO" "Commands and Applications"
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.SH NAME
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.BR cksum ,
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.BR sum
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\- display file checksums and block counts
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.SH SYNOPSIS
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.BR cksum
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.RB [ "-o 1" " | " 2 " | " 3
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.RI "] [" file\0 ...]
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.PP
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.BR sum
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.RI [ file\0 ...]
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.SH DESCRIPTION
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The
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.BR cksum
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utility writes to the standard output three whitespace separated
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fields for each input file.
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These fields are a checksum
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.BR CRC ,
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the total number of octets in the file and the file name.
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If no file name is specified, the standard input is used and no file name
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is written.
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.PP
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The
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.BR sum
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utility is identical to the
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.BR cksum
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utility, except that it defaults to using historic algorithm 1,
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described below.
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It is provided for compatibility.
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You can either install the
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.BR sum
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program (which has the same content as the
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.BR cksum
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program file) or create a
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.IR gsh (1)
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alias that invokes
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.BR cksum :
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.nf
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alias sum "cksum -o 1"
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.fi
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.PP
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The program options are as follows:
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.RS
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.IP \fB-o\fR
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Use historic algorithms instead of the (superior) default one.
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.PP
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.RS
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Algorithm 1 is the algorithm used by historic
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systems as the
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.BR sum (1)
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algorithm and by historic
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systems as the
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.BR sum
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algorithm when using the
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.BR -r
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option.
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This is a 16-bit checksum, with a right rotation before each addition;
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overflow is discarded.
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.PP
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.RS
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Algorithm 2 is the algorithm used by historic
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systems as the
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default
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.BR sum
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algorithm.
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This is a 32-bit checksum, and is defined as follows:
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.nf
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s = sum of all bytes;
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r = s % 2^16 + (s % 2^32) / 2^16;
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cksum = (r % 2^16) + r / 2^16;
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.fi
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.PP
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.RS
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Algorithm 3, a 32-bit checksum, is commonly called the
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.BR "32bit CRC"
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algorithm.
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.PP
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.RS
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Algorithms 1 and 2 write the same fields as
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the default algorithm except the size of the file is
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expressed in blocks.
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For historic reasons, the block size is 1024 for algorithm 1 and 512
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for algorithm 2.
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Partial blocks are rounded up.
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.RE
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.PP
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The default
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.BR CRC
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used is based on the polynomial used for
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.BR CRC
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error checking
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in the networking standard
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POSIX-3.
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The
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.BR CRC
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checksum encoding is defined by the generating polynomial:
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.PP
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.nf
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G(x) = x^32 + x^26 + x^23 + x^22 + x^16 + x^12 +
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x^11 + x^10 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1
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.fi
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.PP
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Mathematically, the
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.BR CRC
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value corresponding to a given file is defined by
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the following procedure:
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.PP
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.RS
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The
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.BR n
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bits to be evaluated are considered to be the coefficients of a mod 2
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polynomial M(x) of degree
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.BR n-1 .
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These
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.BR n
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bits are the bits from the file, with the most significant bit being the most
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significant bit of the first octet of the file and the last bit being the least
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significant bit of the last octet, padded with zero bits (if necessary) to
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achieve an integral number of octets, followed by one or more octets
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representing the length of the file as a binary value, least significant octet
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first.
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The smallest number of octets capable of representing this integer are used.
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.PP
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.RS
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M(x) is multiplied by x^32 (i.e., shifted left 32 bits) and divided by
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G(x) using mod 2 division, producing a remainder R(x) of degree <= 31.
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The coefficients of R(x) are considered to be a 32-bit sequence.
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The bit sequence is complemented and the result is the CRC.
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.PP
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.RS
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The default calculation is identical to that given in pseudo-code
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in the
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article "Computation of Cyclic Redundancy Checks Via Table Lookup"
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by
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Dilip V. Sarwate,
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.IR "Communications of the ACM" ", August 1988."
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.RE
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.PP
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The
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.BR cksum
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and
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.BR sum
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utilities exit 0 on success, and >0 if an error occurs.
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.SH VERSION
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This manual page documents
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.BR cksum
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version 2.0.
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.SH ATTRIBUTIONS
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This command was ported from FreeBSD source code
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for distribution with GNO/ME 2.0.6.
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.SH HISTORY
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A version of
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.BR sum
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translated from GNU code in 1991 by Marek Pawlowski was distributed with
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earlier releases of GNO. Unfortunately, as that version reads files it
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translates carriage return characters into new line characters. To use
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.BR cksum
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to calulate a checksum that matches the old
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.BR sum ,
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use
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.IR tr (1)
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to translate the input stream. For example,
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.nf
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tr '\\r' '\\n' < filename | cksum -o 1
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.fi
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.SH STANDARDS
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The
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.BR cksum
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utility is expected to conform to
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POSIX-2.
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