Manual page for DD(1)
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
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
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-exclusive keyword.
Created by unroff & hp-tools.
© somebody (See intro for details). All Rights Reserved.
Last modified 11/5/97
