dd -- Command

Convert the contents of a file
dd [option=value] ...

dd  copies an  input file  to  an output  file, while  performing requested
conversions.   Options include  case  and character  set conversions,  byte
swapping  conversion for  other machines,  and  different input  and output
buffer sizes.  dd  can be used with raw disk  files or raw tape files to do
efficient copies with large  block (record) sizes.  Read and write requests
can be changed with the bs option described below.

The following  list gives each available option.  Any numbers which specify
block sizes  or seek positions  may be written  in several ways.   A number
followed by w, b, or k  is multiplied by two (for words), 512 (for blocks),
or 1,024  (for kilobytes),  respectively, to obtain  the size in  bytes.  A
pair of such  numbers separated by x is multiplied  together to produce the
size.  All buffer sizes default to 512 bytes if not specified.

bs=n    Set the size of the buffer for both input and output to n bytes.

cbs=n   Set the conversion buffer size to n bytes (used only with character
        set conversions between ASCII and EBCDIC).

conv=list
        Perform conversions  specified by  the comma-separated  list, which
        may include the following:

        ascii     Convert EBCDIC to ASCII
        ebcdic    Convert ASCII to EBCDIC
        ibm       Convert ASCII to EBCDIC, IBM flavor
        lcase     Convert upper case to lower
        noerror   Continue processing on I/O errors
        swab      Swap every pair of bytes before output
        sync      Pad input buffers with 0 bytes to size of ibs
        ucase     Convert lower case to upper


count=n
        Copy a maximum of n input records.

files=n
        Copy a maximum of n input files (useful for multifile tapes).

ibs=n   Set the input buffer  size to n (normally used  if input and output
        blocking sizes are to be different).

if=file
        Open file for input; the standard  input is used when no if= option
        is given.

obs=n   Set the output buffer size to n.

of=file
        Open file  for output;  the  standard output  is used  when no  of=
        option is given.

seek=n  Seek to position n  bytes into the output  before copying (does not
        work on  stream  data such  as tapes,  communications devices,  and
        pipes).

skip=n  Read and discard the first n input records.

Examples

The first  example copies the entire contents  of a 1.44-megabyte, 3.5-inch
diskette from drive 0 to file disk.dd:

    dd if=/dev/fva0 of=disk.dd bs=36b count=80

The second  example writes the contents of  the previously stored 5.25-inch
file backup.dd to a 1.2-megabyte, 5.25-inch floppy disk in drive 1:

    dd if=backup.dd of=/dev/fha1 bs=30b count=80

See Also

ASCII,
commands,
conv,
cp,
tape,
tr

Diagnostics

The command reports the number of full and partial buffers read and written
upon completion.

Notes

Because of differing interpretations of EBCDIC, especially for certain more
exotic graphic  characters such as braces and  backslash, no one conversion
table  will be  adequate for  all  applications.  The  ebcdic table  is the
American Standard of the Business Equipment Manufacturers Association.  The
ibm table  seems to be  more practical for  line printer codes  at many IBM
installations.

© 2012 by Stephen A. Ness