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OpenDarwin 7.2.1 - man page for dd (opendarwin section 1)

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DD(1)				   BSD General Commands Manual				    DD(1)

NAME
     dd -- convert and copy a file

SYNOPSIS
     dd [operands ...]

DESCRIPTION
     The dd utility copies the standard input to the standard output.  Input data is read and
     written in 512-byte blocks.  If input reads are short, input from multiple reads are aggre-
     gated to form the output block.  When finished, dd displays the number of complete and par-
     tial input and output blocks and truncated input records to the standard error output.

     The following operands are available:

     bs=n     Set both input and output block size to n bytes, superseding the ibs and obs oper-
	      ands.  If no conversion values other than noerror, notrunc or sync are specified,
	      then each input block is copied to the output as a single block without any aggre-
	      gation of short blocks.

     cbs=n    Set the conversion record size to n bytes.  The conversion record size is required
	      by the record oriented conversion values.

     count=n  Copy only n input blocks.

     files=n  Copy n input files before terminating.  This operand is only applicable when the
	      input device is a tape.

     ibs=n    Set the input block size to n bytes instead of the default 512.

     if=file  Read input from file instead of the standard input.

     iseek=n  Seek on the input file n blocks.	This is synonymous with skip=n.

     obs=n    Set the output block size to n bytes instead of the default 512.

     of=file  Write output to file instead of the standard output.  Any regular output file is
	      truncated unless the notrunc conversion value is specified.  If an initial portion
	      of the output file is seeked past (see the oseek operand), the output file is trun-
	      cated at that point.

     oseek=n  Seek on the output file n blocks.  This is synonymous with seek=n.

     seek=n   Seek n blocks from the beginning of the output before copying.  On non-tape
	      devices, an lseek(2) operation is used.  Otherwise, existing blocks are read and
	      the data discarded.  If the user does not have read permission for the tape, it is
	      positioned using the tape ioctl(2) function calls.  If the seek operation is past
	      the end of file, space from the current end of file to the specified offset is
	      filled with blocks of NUL bytes.

     skip=n   Skip n blocks from the beginning of the input before copying.  On input which sup-
	      ports seeks, an lseek(2) operation is used.  Otherwise, input data is read and dis-
	      carded.  For pipes, the correct number of bytes is read.	For all other devices,
	      the correct number of blocks is read without distinguishing between a partial or
	      complete block being read.

     conv=value[,value ...]
	      Where value is one of the symbols from the following list.

	      ascii, oldascii
		       The same as the unblock value except that characters are translated from
		       EBCDIC to ASCII before the records are converted.  (These values imply
		       unblock if the operand cbs is also specified.)  There are two conversion
		       maps for ASCII.	The value ascii specifies the recommended one which is
		       compatible with AT&T System V UNIX.  The value oldascii specifies the one
		       used in historic AT&T UNIX and pre-4.3BSD-Reno systems.

	      block    Treats the input as a sequence of newline or end-of-file terminated vari-
		       able length records independent of input and output block boundaries.  Any
		       trailing newline character is discarded.  Each input record is converted
		       to a fixed length output record where the length is specified by the cbs
		       operand.  Input records shorter than the conversion record size are padded
		       with spaces.  Input records longer than the conversion record size are
		       truncated.  The number of truncated input records, if any, are reported to
		       the standard error output at the completion of the copy.

	      ebcdic, ibm, oldebcdic, oldibm
		       The same as the block value except that characters are translated from
		       ASCII to EBCDIC after the records are converted.  (These values imply
		       block if the operand cbs is also specified.)  There are four conversion
		       maps for EBCDIC.  The value ebcdic specifies the recommended one which is
		       compatible with AT&T System V UNIX.  The value ibm is a slightly different
		       mapping, which is compatible with the AT&T System V UNIX ibm value.  The
		       values oldebcdic and oldibm are maps used in historic AT&T UNIX and
		       pre-4.3BSD-Reno systems.

	      lcase    Transform uppercase characters into lowercase characters.

	      noerror  Do not stop processing on an input error.  When an input error occurs, a
		       diagnostic message followed by the current input and output block counts
		       will be written to the standard error output in the same format as the
		       standard completion message.  If the sync conversion is also specified,
		       any missing input data will be replaced with NUL bytes (or with spaces if
		       a block oriented conversion value was specified) and processed as a normal
		       input buffer.  If the sync conversion is not specified, the input block is
		       omitted from the output.  On input files which are not tapes or pipes, the
		       file offset will be positioned past the block in which the error occurred
		       using lseek(2).

	      notrunc  Do not truncate the output file.  This will preserve any blocks in the
		       output file not explicitly written by dd.  The notrunc value is not sup-
		       ported for tapes.

	      osync    Pad the final output block to the full output block size.  If the input
		       file is not a multiple of the output block size after conversion, this
		       conversion forces the final output block to be the same size as preceding
		       blocks for use on devices that require regularly sized blocks to be writ-
		       ten.  This option is incompatible with use of the bs=n block size specifi-
		       cation.

	      sparse   If one or more output blocks would consist solely of NUL bytes, try to
		       seek the output file by the required space instead of filling them with
		       NULs, resulting in a sparse file.

	      swab     Swap every pair of input bytes.	If an input buffer has an odd number of
		       bytes, the last byte will be ignored during swapping.

	      sync     Pad every input block to the input buffer size.	Spaces are used for pad
		       bytes if a block oriented conversion value is specified, otherwise NUL
		       bytes are used.

	      ucase    Transform lowercase characters into uppercase characters.

	      unblock  Treats the input as a sequence of fixed length records independent of
		       input and output block boundaries.  The length of the input records is
		       specified by the cbs operand.  Any trailing space characters are discarded
		       and a newline character is appended.

     Where sizes are specified, a decimal, octal, or hexadecimal number of bytes is expected.  If
     the number ends with a ``b'', ``k'', ``m'', ``g'', or ``w'', the number is multiplied by
     512, 1024 (1K), 1048576 (1M), 1073741824 (1G) or the number of bytes in an integer, respec-
     tively.  Two or more numbers may be separated by an ``x'' to indicate a product.

     When finished, dd displays the number of complete and partial input and output blocks, trun-
     cated input records and odd-length byte-swapping blocks to the standard error output.  A
     partial input block is one where less than the input block size was read.	A partial output
     block is one where less than the output block size was written.  Partial output blocks to
     tape devices are considered fatal errors.	Otherwise, the rest of the block will be written.
     Partial output blocks to character devices will produce a warning message.  A truncated
     input block is one where a variable length record oriented conversion value was specified
     and the input line was too long to fit in the conversion record or was not newline termi-
     nated.

     Normally, data resulting from input or conversion or both are aggregated into output blocks
     of the specified size.  After the end of input is reached, any remaining output is written
     as a block.  This means that the final output block may be shorter than the output block
     size.

     If dd receives a SIGINFO (see the status argument for stty(1)) signal, the current input and
     output block counts will be written to the standard error output in the same format as the
     standard completion message.  If dd receives a SIGINT signal, the current input and output
     block counts will be written to the standard error output in the same format as the standard
     completion message and dd will exit.

DIAGNOSTICS
     The dd utility exits 0 on success, and >0 if an error occurs.

SEE ALSO
     cp(1), mt(1), tr(1)

STANDARDS
     The dd utility is expected to be a superset of the IEEE Std 1003.2 (``POSIX.2'') standard.
     The files operand and the ascii, ebcdic, ibm, oldascii, oldebcdic and oldibm values are
     extensions to the POSIX standard.

BSD					 January 13, 1994				      BSD
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