dd(C)                         06 January 1993                          dd(C)


 Name

    dd - convert and copy a file

 Syntax

    dd [ option=value ] ...

 Description

    dd copies the specified input file to the specified output with possible
    conversions. The standard input and output are used by default.  The
    input and output block size may be specified to take advantage of raw
    physical I/O.

    if=file        Input filename; standard input is default.

    of=file        Output filename; standard output is default. This option
                   does not truncate an existing file.

    ibs=n          Input block size is n bytes (default is BSIZE block size).

    obs=n          Output block size (default is BSIZE block size).

    bs=n           Sets both input and output block size, superseding ibs and
                   obs.  If no conversion is specified, it is particularly
                   efficient since no in-core copy needs to be done.

    cbs=n          Conversion buffer size.

    skip=n         Skips n input records before starting copy. (The records
                   are read but not output.)

    seek=n         Seeks n records from beginning of output file before copy-
                   ing.

    iseek=n        Same as skip, but seeks over the records (that is, uses
                   iseek(S)) instead of reading them.

    oseek=n        As for seek.

    files=n        Specify the number of input files to concatenate. This
                   option effectively causes a sequence of n EOFs to be
                   ignored.  (It is generally only useful for tape.)

    conv=block     Convert ASCII to unblocked ASCII.

    conv=unblock   Convert unblocked ASCII to ASCII.

    count=n        Copies only n input records.

    conv=ascii     Converts EBCDIC to ASCII.

    conv=ebcdic    Converts ASCII to EBCDIC.

    conv=ibm       Slightly different map of ASCII to EBCDIC.

    conv=lcase     Maps alphabetic characters to lowercase.

    conv=ucase     Maps alphabetic characters to uppercase.

    conv=swab      Swaps every pair of bytes.

    conv=noerror   Does not stop processing on an error.

    conv=sync      Pads every input record to ibs.

    conv=... , ... Several comma-separated conversions.

    Where sizes are specified, a number of bytes is expected.  A number may
    end with k, b, or w to specify multiplication by 1024, 512, or 2 respec-
    tively; a pair of numbers may be separated by x to indicate a product.

    cbs is used only if ascii, ebcdic, or ibm conversion is specified.  In
    the former case, cbs characters are placed into the conversion buffer,
    converted to ASCII, and trailing blanks trimmed and newline added before
    sending the line to the output.  In the latter two cases, ASCII charac-
    ters are read into the conversion buffer, converted to EBCDIC, and blanks
    added to make up an output record of size cbs.

    After completion, dd reports the number of whole and partial input and
    output blocks.

 Examples

    The first example reads an EBCDIC tape, blocked ten 80-byte EBCDIC card
    images per record, into the ASCII file outfile:

       dd  if=/dev/rct0  of=outfile  ibs=800  cbs=80  conv=ascii,lcase

    Note the use of raw magtape.  dd is especially suited to I/O on raw phy-
    sical devices because it allows reading and writing in arbitrary record
    sizes.

    The next example shows how to copy the contents of one floppy disk to
    another, using /tmp as a temporary storage area. The source disk is
    inserted in the drive, and the following command entered:

       dd if=/dev/rfd0 of=/tmp/tempfile

    Next the source disk is removed from the drive, and the destination disk
    inserted. The data in the temporary file, /tmp/tempfile, may now be
    copied to this disk:

       dd if=/tmp/tempfile of=/dev/rfd0

    Finally remove the temporary file:

       rm /tmp/tempfile


 See also

    copy(C), cp(C) and tar(C).

 Diagnostics

    f+p records in(out)     Numbers of full and partial records read (writ-
                            ten).

 Notes

    The ASCII/EBCDIC conversion tables are taken from the 256-character stan-
    dard in the CACM Nov, 1968.  The ibm conversion corresponds better to
    certain IBM print train conventions. There is no universal solution.

    Newlines are inserted only on conversion to ASCII; padding is done only
    on conversion to EBCDIC.

    When using dd with a raw device, specify the block size as a multiple of
    1K.  For example, to use a 9K block size, enter:

       dd if=file of=/dev/rct0 bs=18b

    You could also enter:

       dd if=file of=/dev/rct0 bs=9k


 Standards conformance

    dd is conformant with:

    AT&T SVID Issue 2;
    and X/Open Portability Guide, Issue 3, 1989.