4.3BSD - /usr/man/cat1/dd.0

DD(1)                                                                    DD(1)


NAME
       dd - convert and copy a file

SYNOPSIS
       dd [option=value] ...

DESCRIPTION
       Dd  copies the specified input file to the specified output with possi‐
       ble 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.

       option         values
       if=            input file name; standard input is default
       of=            output file name; standard output is default
       ibs=n          input block size n bytes (default 512)
       obs=n          output block size (default 512)
       bs=n           set both input and output block  size,  superseding  ibs
                      and obs; also, if no conversion is specified, it is par‐
                      ticularly efficient since no copy need be done
       cbs=n          conversion buffer size
       skip=n         skip n input records before starting copy
       files=n        copy n input files before terminating (makes sense  only
                      where input is a magtape or similar device).
       seek=n         seek  n  records  from  beginning  of output file before
                      copying
       count=n        copy only n input records
       conv=ascii     convert EBCDIC to ASCII
            ebcdic    convert ASCII to EBCDIC
            ibm       slightly different map of ASCII to EBCDIC
            block     convert variable length records to fixed length
            unblock   convert fixed length records to variable length
            lcase     map alphabetics to lower case
            ucase     map alphabetics to upper case
            swab      swap every pair of bytes
            noerror   do not stop processing on an error
            sync      pad every input record to ibs
            ... , ... 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, unblock, ebcdic, ibm, or block conversion is
       specified.  In the first two cases, cbs characters are placed into  the
       conversion  buffer,  any  specified character mapping is done, trailing
       blanks trimmed and new-line added before sending the line to  the  out‐
       put.   In  the latter three cases, characters are read into the conver‐
       sion buffer, 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.

       For example, to read an EBCDIC tape blocked  ten  80-byte  EBCDIC  card
       images per record into the ASCII file x:

              dd if=/dev/rmt0 of=x ibs=800 cbs=80 conv=ascii,lcase

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

SEE ALSO
       cp(1), tr(1)

DIAGNOSTICS
       f+p records in(out): numbers of full and partial records read(written)

BUGS
       The  ASCII/EBCDIC  conversion  tables  are taken from the 256 character
       standard in the CACM Nov,  1968.   The  ‘ibm’  conversion,  while  less
       blessed  as  a  standard, corresponds better to certain IBM print train
       conventions.  There is no universal solution.
       One must specify ‘‘conv=noerror,sync’’ when copying raw disks with  bad
       sectors to insure dd stays synchronized.

       Certain combinations of arguments to conv= are permitted.  However, the
       block or unblock option cannot be combined with ascii, ebcdic  or  ibm.
       Invalid  combinations  silently ignore all but the last mutually-exclu‐
       sive keyword.


4th Berkeley Distribution       April 29, 1985                           DD(1)