DD(1)                      OpenBSD Reference 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, applying
     any specified conversions.  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 partial input and output blocks and truncated input records
     to the standard error output.

     The following operands are available:

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

     of=file  Write output to file instead of the standard output.  Any regu-
              lar output file is truncated unless the notrunc conversion value
              is specified.  If an initial portion of the output file is
              skipped (see the seek operand), the output file is truncated at
              that point.

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

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

     bs=n     Set both the 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 aggrega-
              tion of short blocks.

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

     count=n  Copy only n input blocks.

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

     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 us-
              ing 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 conver-
                       sion maps for ASCII. The value ascii specifies the rec-
                       ommended one which is compatible with System V.  The
                       value oldascii specifies the one used in historic AT&T
                       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 new-
                       line character is discarded.  Each input record is con-
                       verted 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 and pre-4.3BSD-reno systems.

              lcase    Transform uppercase characters into lowercase charac-
                       ters.

              noerror  Do not stop processing on an input error.  When an in-
                       put 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 con-
                       version 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 out-
                       put 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.

              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 charac-
                       ters.

              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 number of bytes is expected.  If the
     number ends with a `b', `k', `m', or `w', the number is multiplied by
     512, 1024 (1K), 1048576 (1M), or the number of bytes in an integer, re-
     spectively.  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 vari-
     able length record oriented conversion value was specified and the input
     line was too long to fit in the conversion record or was not newline ter-
     minated.

     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))  sig-
     nal, the current input and output block counts will be written to the
     standard error output in the same format as the standard completion mes-
     sage.  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.

     The dd utility exits 0 on success or >0 if an error occurred.

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

STANDARDS
     The dd utility is expected to be a superset of the IEEE Std1003.2
     (``POSIX.2'') standard.  The files operand and the ascii, ebcdic, ibm,
     oldascii, oldebcdic, and oldibm values are extensions to the POSIX stan-
     dard.

OpenBSD 2.6                    January 13, 1994                              3