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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 aggregated to form the output
     block.  When finished, dd displays the number of complete and partial input and output blocks and trun-cated truncated
     cated 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 char-acter character
                       acter 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 conver-sion conversion
                       sion 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 pro-cessed processed
                       cessed 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 out-put output
                       put 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 out-put output
                       put block boundaries.  The length of the input records is specified by the cbs oper-and. operand.
                       and.  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 out-put output
     put block size was written.  Partial output blocks to tape devices are considered fatal errors.  Other-wise, Otherwise,
     wise, 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), 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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