DD

Section: User Commands (1)
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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=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 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 files from (tape) input
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
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 or ebcdic conversion is specified. In the former case cbs characters are placed into the conversion 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

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.

To skip over a file before copying from magnetic tape do

(dd of=/dev/null; dd of=x) </dev/rmt0
 

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.

Newlines are inserted only on conversion to ASCII; padding is done only on conversion to EBCDIC. These should be separate options.


 

Index

NAME
SYNOPSIS
DESCRIPTION
SEE ALSO
DIAGNOSTICS
BUGS

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Time: 10:16:20 GMT, December 28, 2024