NAME
dd - convert and copy a file
SYNOPSIS
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.
option values
if= input file name; standard input is default
of= output file name; standard output is default
ibs= input block size (default 512)
obs= output block size (default 512)
bs= set both input and output block size, super-
seding ibs and obs; also, if no conversion is
specified, it is particularly efficient since
no copy need be done
cbs=n conversion buffer size
skip=n skip n input records before starting copy
count=n copy only n input records
conv=ascii convert EBCDIC to ASCII
ebcdic convert ASCII to EBCDIC
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
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. Also a pair of numbers may be
separated by x to indicate a product.
Cbs is used only if ascii or ebcdic conversion is specified.
In the former case cbs characters are placed into the con-
version buffer, converted to ASCII, and trailing blanks
trimmed and new-line added before sending the line to the
output. In the latter case ASCII characters 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.
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
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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 (I)
BUGS
The ASCII/EBCDIC conversion tables are taken from the 256
character standard in the CACM Nov, 1968. It is not clear
how this relates to real life.
Newlines are inserted only on conversion to ASCII; padding
is done only on conversion to EBCDIC. There should be sepa-
rate options.
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