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DD(1)                   FreeBSD 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 aggregated to form the output block.  When
     finished, dd displays the number of complete and partial 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 operands.  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 aggregation
              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
              truncated 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 supports seeks, an lseek(2) operation is used.
              Otherwise, input data is read and discarded.  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 variable 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
                           supported 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 written.  This option
                           is incompatible with use of the bs=n block size
                           specification.

              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, respectively.  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, truncated 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 terminated.

     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.

FreeBSD 11.0-PRERELEASE        January 13, 1994        FreeBSD 11.0-PRERELEASE

NAME | SYNOPSIS | DESCRIPTION | DIAGNOSTICS | SEE ALSO | STANDARDS

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