9e69bea9f1
to specify an alternative padding character when using a conversion mode, or when using noerror with sync and an input error occurs. This facilities reading old and error-prone media by allowing the user to more effectively mark error blocks in the output stream.
414 lines
12 KiB
Groff
414 lines
12 KiB
Groff
.\" Copyright (c) 1990, 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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.\" Keith Muller of the University of California, San Diego.
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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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.\" 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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.\" @(#)dd.1 8.2 (Berkeley) 1/13/94
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.\" $FreeBSD$
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.\"
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.Dd March 5, 2004
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.Dt DD 1
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.Os
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.Sh NAME
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.Nm dd
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.Nd convert and copy a file
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.Sh SYNOPSIS
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.Nm
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.Op Ar operands ...
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.Sh DESCRIPTION
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The
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.Nm
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utility copies the standard input to the standard output.
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Input data is read and written in 512-byte blocks.
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If input reads are short, input from multiple reads are aggregated
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to form the output block.
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When finished,
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.Nm
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displays the number of complete and partial input and output blocks
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and truncated input records to the standard error output.
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.Pp
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The following operands are available:
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.Bl -tag -width ".Cm of Ns = Ns Ar file"
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.It Cm bs Ns = Ns Ar n
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Set both input and output block size to
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.Ar n
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bytes, superseding the
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.Cm ibs
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and
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.Cm obs
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operands.
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If no conversion values other than
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.Cm noerror ,
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.Cm notrunc
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or
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.Cm sync
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are specified, then each input block is copied to the output as a
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single block without any aggregation of short blocks.
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.It Cm cbs Ns = Ns Ar n
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Set the conversion record size to
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.Ar n
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bytes.
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The conversion record size is required by the record oriented conversion
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values.
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.It Cm count Ns = Ns Ar n
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Copy only
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.Ar n
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input blocks.
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.It Cm files Ns = Ns Ar n
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Copy
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.Ar n
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input files before terminating.
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This operand is only applicable when the input device is a tape.
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.It Cm fillchar Ns = Ns Ar c
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When padding a block in conversion mode or due to use of
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.Cm noerror
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and
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.Cm sync
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modes, fill with the specified ASCII character, rather than using a space
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or nul.
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.It Cm ibs Ns = Ns Ar n
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Set the input block size to
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.Ar n
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bytes instead of the default 512.
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.It Cm if Ns = Ns Ar file
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Read input from
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.Ar file
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instead of the standard input.
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.It Cm iseek Ns = Ns Ar n
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Seek on the input file
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.Ar n
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blocks.
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This is synonymous with
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.Cm skip Ns = Ns Ar n .
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.It Cm obs Ns = Ns Ar n
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Set the output block size to
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.Ar n
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bytes instead of the default 512.
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.It Cm of Ns = Ns Ar file
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Write output to
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.Ar file
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instead of the standard output.
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Any regular output file is truncated unless the
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.Cm notrunc
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conversion value is specified.
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If an initial portion of the output file is seeked past (see the
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.Cm oseek
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operand),
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the output file is truncated at that point.
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.It Cm oseek Ns = Ns Ar n
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Seek on the output file
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.Ar n
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blocks.
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This is synonymous with
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.Cm seek Ns = Ns Ar n .
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.It Cm seek Ns = Ns Ar n
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Seek
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.Ar n
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blocks from the beginning of the output before copying.
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On non-tape devices, an
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.Xr lseek 2
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operation is used.
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Otherwise, existing blocks are read and the data discarded.
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If the user does not have read permission for the tape, it is positioned
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using the tape
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.Xr ioctl 2
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function calls.
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If the seek operation is past the end of file, space from the current
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end of file to the specified offset is filled with blocks of
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.Dv NUL
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bytes.
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.It Cm skip Ns = Ns Ar n
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Skip
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.Ar n
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blocks from the beginning of the input before copying.
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On input which supports seeks, an
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.Xr lseek 2
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operation is used.
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Otherwise, input data is read and discarded.
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For pipes, the correct number of bytes is read.
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For all other devices, the correct number of blocks is read without
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distinguishing between a partial or complete block being read.
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.It Cm conv Ns = Ns Ar value Ns Op , Ns Ar value ...
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Where
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.Cm value
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is one of the symbols from the following list.
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.Bl -tag -width ".Cm unblock"
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.It Cm ascii , oldascii
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The same as the
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.Cm unblock
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value except that characters are translated from
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.Tn EBCDIC
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to
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.Tn ASCII
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before the
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records are converted.
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(These values imply
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.Cm unblock
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if the operand
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.Cm cbs
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is also specified.)
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There are two conversion maps for
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.Tn ASCII .
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The value
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.Cm ascii
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specifies the recommended one which is compatible with
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.At V .
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The value
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.Cm oldascii
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specifies the one used in historic
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.At
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and
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.No pre- Ns Bx 4.3 reno
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systems.
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.It Cm block
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Treats the input as a sequence of newline or end-of-file terminated variable
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length records independent of input and output block boundaries.
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Any trailing newline character is discarded.
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Each input record is converted to a fixed length output record where the
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length is specified by the
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.Cm cbs
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operand.
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Input records shorter than the conversion record size are padded with spaces.
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Input records longer than the conversion record size are truncated.
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The number of truncated input records, if any, are reported to the standard
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error output at the completion of the copy.
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.It Cm ebcdic , ibm , oldebcdic , oldibm
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The same as the
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.Cm block
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value except that characters are translated from
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.Tn ASCII
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to
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.Tn EBCDIC
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after the
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records are converted.
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(These values imply
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.Cm block
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if the operand
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.Cm cbs
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is also specified.)
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There are four conversion maps for
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.Tn EBCDIC .
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The value
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.Cm ebcdic
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specifies the recommended one which is compatible with
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.At V .
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The value
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.Cm ibm
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is a slightly different mapping, which is compatible with the
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.At V
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.Cm ibm
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value.
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The values
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.Cm oldebcdic
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and
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.Cm oldibm
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are maps used in historic
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.At
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and
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.No pre- Ns Bx 4.3 reno
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systems.
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.It Cm lcase
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Transform uppercase characters into lowercase characters.
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.It Cm pareven , parnone , parodd , parset
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Output data with the specified parity.
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The parity bit on input is stripped unless
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.Tn EBCDIC
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to
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.Tn ASCII
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conversions is also specified.
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.It Cm noerror
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Do not stop processing on an input error.
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When an input error occurs, a diagnostic message followed by the current
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input and output block counts will be written to the standard error output
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in the same format as the standard completion message.
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If the
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.Cm sync
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conversion is also specified, any missing input data will be replaced
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with
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.Dv NUL
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bytes (or with spaces if a block oriented conversion value was
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specified) and processed as a normal input buffer.
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If the
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.Cm fillchar
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option is specified, the fill char provided on the command line will override
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the automatic selection of fill character.
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If the
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.Cm sync
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conversion is not specified, the input block is omitted from the output.
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On input files which are not tapes or pipes, the file offset
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will be positioned past the block in which the error occurred using
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.Xr lseek 2 .
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.It Cm notrunc
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Do not truncate the output file.
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This will preserve any blocks in the output file not explicitly written
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by
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.Nm .
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The
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.Cm notrunc
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value is not supported for tapes.
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.It Cm osync
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Pad the final output block to the full output block size.
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If the input file is not a multiple of the output block size
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after conversion, this conversion forces the final output block
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to be the same size as preceding blocks for use on devices that require
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regularly sized blocks to be written.
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This option is incompatible with use of the
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.Cm bs Ns = Ns Ar n
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block size specification.
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.It Cm sparse
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If one or more output blocks would consist solely of
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.Dv NUL
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bytes, try to seek the output file by the required space instead of
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filling them with
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.Dv NUL Ns s ,
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resulting in a sparse file.
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.It Cm swab
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Swap every pair of input bytes.
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If an input buffer has an odd number of bytes, the last byte will be
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ignored during swapping.
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.It Cm sync
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Pad every input block to the input buffer size.
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Spaces are used for pad bytes if a block oriented conversion value is
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specified, otherwise
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.Dv NUL
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bytes are used.
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.It Cm ucase
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Transform lowercase characters into uppercase characters.
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.It Cm unblock
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Treats the input as a sequence of fixed length records independent of input
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and output block boundaries.
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The length of the input records is specified by the
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.Cm cbs
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operand.
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Any trailing space characters are discarded and a newline character is
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appended.
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.El
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.El
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.Pp
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Where sizes are specified, a decimal, octal, or hexadecimal number of
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bytes is expected.
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If the number ends with a
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.Dq Li b ,
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.Dq Li k ,
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.Dq Li m ,
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.Dq Li g ,
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or
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.Dq Li w ,
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the
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number is multiplied by 512, 1024 (1K), 1048576 (1M), 1073741824 (1G)
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or the number of bytes in an integer, respectively.
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Two or more numbers may be separated by an
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.Dq Li x
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to indicate a product.
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.Pp
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When finished,
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.Nm
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displays the number of complete and partial input and output blocks,
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truncated input records and odd-length byte-swapping blocks to the
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standard error output.
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A partial input block is one where less than the input block size
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was read.
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A partial output block is one where less than the output block size
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was written.
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Partial output blocks to tape devices are considered fatal errors.
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Otherwise, the rest of the block will be written.
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Partial output blocks to character devices will produce a warning message.
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A truncated input block is one where a variable length record oriented
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conversion value was specified and the input line was too long to
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fit in the conversion record or was not newline terminated.
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.Pp
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Normally, data resulting from input or conversion or both are aggregated
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into output blocks of the specified size.
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After the end of input is reached, any remaining output is written as
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a block.
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This means that the final output block may be shorter than the output
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block size.
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.Pp
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If
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.Nm
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receives a
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.Dv SIGINFO
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(see the
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.Cm status
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argument for
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.Xr stty 1 )
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signal, the current input and output block counts will
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be written to the standard error output
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in the same format as the standard completion message.
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If
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.Nm
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receives a
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.Dv SIGINT
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signal, the current input and output block counts will
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be written to the standard error output
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in the same format as the standard completion message and
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.Nm
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will exit.
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.Sh EXAMPLES
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Check that a disk drive contains no bad blocks:
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.Pp
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.Dl "dd if=/dev/ad0 of=/dev/null bs=1m"
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.Pp
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Do a refresh of a disk drive, in order to prevent presently
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recoverable read errors from progressing into unrecoverable read errors:
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.Pp
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.Dl "dd if=/dev/ad0 of=/dev/ad0 bs=1m"
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.Pp
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Remove parity bit from a file:
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.Pp
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.Dl "dd if=file conv=parnone of=file.txt"
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.Pp
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Check for (even) parity errors on a file:
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.Pp
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.Dl "dd if=file conv=pareven | cmp -x - file"
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.Sh DIAGNOSTICS
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.Ex -std
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.Sh SEE ALSO
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.Xr cp 1 ,
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.Xr mt 1 ,
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.Xr tr 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
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standard.
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The
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.Cm files
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operand and the
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.Cm ascii ,
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.Cm ebcdic ,
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.Cm ibm ,
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.Cm oldascii ,
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.Cm oldebcdic
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and
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.Cm oldibm
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values are extensions to the
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.Tn POSIX
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standard.
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