DD(1) General Commands Manual DD(1)
dd - convert and copy files with various data formats
dd [ option=value ] ...
dd copies a specified input file to a 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
if=name Input file is taken from name; standard input is
of=name Output file is taken from name; standard output is
default. Note: dd creates an explicit output file;
therefore the seek option is usually useless with
explicit output except in special cases such as using
magnetic tape or raw disk files.
ibs=n Input block size n bytes (default 512).
obs=n Output block size n bytes (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. Block
sizes for the Sun386i are 9k for 3.5-inch floppy disks,
and 126b (blocks) for quarter-inch tapes.
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
when input is a magtape or similar device).
seek=n Seek n records from beginning of output file before
copying. This option generally only works with magnetic
tapes and raw disk files and is otherwise usually use-
less if the explicit output file was named with the of
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, for a combination
of effects. For instance, conv=sync,block is useful for
reading variable-length output from a pipe.
Where sizes are specified, a number of bytes is expected. A number may
end with k (kilobytes) to specify multiplication by 1024, b (blocks of
512 bytes) to specify multiplication by 512, or w (words) to specify
multiplication by 4; a pair of numbers may be separated by x to indi-
cate 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 NEWLINE added before sending the line to the output.
In the latter three cases, characters are read into the conversion buf-
fer, and blanks added to make up an output record of size cbs.
After completion, dd reports the number of whole and partial input and
To read an EBCDIC tape blocked ten 80-byte EBCDIC card images per
record into the ASCII file x:
example% 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
The following write the file filename to a 3.5-inch floppy and read
from the floppy into a file filename, respectively:
example% dd if=filename of=/dev/rfd0c bs=9k
example% dd if=/dev/rfd0c of=filename bs=9k
Sun386i files names are shown in fdformat(1).
cp(1), fdformat(1), tr(1V)
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 conven-
tions. There is no universal solution.
The block and unblock options cannot be combined with the ascii, ebcdic
or ibm. Invalid combinations silently ignore all but the last mutu-
28 January 1988 DD(1)