DD(1) General Commands Manual DD(1)
dd - convert and copy a file
dd [option=value] ...
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= 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 particularly effi-
cient 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
respectively; 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
output. In the latter three cases, characters are read into the conversion buffer, and blanks added to make up an output record of size
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
f+p records in(out): numbers of full and partial records read(written)
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-exclusive keyword.
4th Berkeley Distribution April 29, 1985 DD(1)