DD(1) General Commands Manual DD(1)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. The options are
-if f Open file f for input.
-of f Open file f for output.
-ibs n Set input block size to n bytes (default 512).
-obs n Set output block size (default 512).
-bs n Set both input and output block size, superseding ibs and obs. If no conversion is specified, preserve the input block size
instead of packing short blocks into the output buffer. This is particularly efficient since no in-core copy need be done.
-cbs n Set conversion buffer size.
-skip n Skip n input records before copying.
-iseek n
Seek n records forward on input file before copying.
-files n
Catenate n input files (useful only for magnetic tape or similar input device).
-oseek 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 Like ebcdic but with a slightly different character map.
block Convert variable length ASCII records to fixed length.
unblock Convert fixed length ASCII 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 bytes.
Where sizes are specified, a number of bytes is expected. A number may end with or to specify multiplication by 1024 or 512 respectively;
a pair of numbers may be separated by to indicate a product. Multiple conversions may be specified in the style:
is used only if or conversion is specified. In the first two cases, n characters are copied into the conversion buffer, any specified
character mapping is done, trailing blanks are trimmed and new-line is added before sending the line to the output. In the latter three
cases, characters are read into the conversion buffer and blanks are added to make up an output record of size n. If is unspecified or
zero, the and options convert the character set without changing the block structure of the input file; the and options become a simple
file copy.
SOURCE
/sys/src/cmd/dd.c
SEE ALSO cp(1)DIAGNOSTICS
Dd reports the number of full + partial input and output blocks handled.
DD(1)
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dd(1) General Commands Manual dd(1)Name
dd - copy and convert data
Syntax
dd [option = value...]
Description
The command copies an input file to an output with any requested conversions. The command is especially suited to I/O on the raw physical
devices because it allows reading and writing in arbitrary record sizes.
After completion, reports the number of whole and partial input and output blocks.
This utility supports EOT handling which allows the use of multiple media. The utility prompts for the next volume when it encounters the
end of the current volume.
Options
Where sizes (n) are given for an option, the number may end with k for kilobytes (1024 bytes), b for blocks (512 bytes), or w for words (2
bytes). Also, two numbers may be separated by the character x to indicate a product.
if=name Input file name. The standard input is the default.
of=name Output file name. The standard output is the default.
ibs=n Input block size, n bytes. The default is 512 bytes. Some devices do not support greater than 65,535 bytes.
obs=n Output block size, n bytes. The default is 512 bytes. Some devices do not support greater than 65,535 bytes.
bs=n Set both input and output block size to n bytes, superseding ibs and obs. Also, if bs is specified, the copy is more
efficient, since no blocking conversion is necessary.
cbs=n Conversion buffer size, n bytes. Use only if ascii, unblock, ebcdic, ibm, or block conversion is specified. For ascii
and unblock, n characters are placed into the conversion buffer, any specified character mapping is done, trailing
blanks are trimmed and new line added before sending the line to the output. For ebcdic, ibm, or block, characters are
read into the conversion buffer, and blanks added to make an output record of size n bytes.
skip=n Skip n input records before starting to copy.
files=n Copy n input files before terminating. This option is useful only when the input is a magnetic tape or similar device.
seek=n Seek n records from beginning of output file before copying.
rbuf=n Use n buffers for reading from those raw devices that support n-buffered I/O. (See Section 4 to check whether a spe-
cific device supports n-buffered I/O.) All n reads are started and each read must complete before the data can be
used. This allows an n-buffered read-ahead on supported raw devices.
A default of eight read buffers are used if the read device supports n-buffered I/O and the write device does not.
The rbuf option cannot be used with the wbuf option.
wbuf=n Use n buffers for writing from those raw devices that support n-buffered I/O. (See Section 4 to check whether a spe-
cific device supports n-buffered I/O.) Each write is started but not known to be complete until all n buffers have
been used. (This allows an n-buffered write-behind on supported raw devices).
A default of eight write buffers are used if the write device supports n-buffered I/O.
The wbuf option cannot be used with the rbuf option.
count=n Copy only n input records.
conv=ascii Convert EBCDIC to ASCII.
conv=ebcdic Convert ASCII to EBCDIC.
conv=ibm Slightly different map of ASCII to EBCDIC (see RESTRICTIONS).
conv=block Convert variable length records to fixed length.
conv=unblock Convert fixed length records to variable length.
conv=lcase Map alphabetics to lower case.
conv=ucase Map alphabetics to upper case.
conv=swab Swap every pair of bytes.
conv=noerror Do not stop processing on an error.
conv=sync Pad every input record to ibs.
conv=nomulti Disable multiple tape volumes.
conv=sparse Create a sparse output file.
conv=... , ... Include several arguments for the conv option, separated by commas (see example below).
Examples
The following example shows how to read an EBCDIC tape blocked ten 80-byte EBCDIC card images per record into the ASCII file x:
dd if=/dev/rmt0h of=x ibs=800 cbs=80 conv=ascii,lcase
Note the use of raw magtape. As noted in the DESCRIPTION, the command is especially suited to I/O on the raw physical devices because it
allows reading and writing in arbitrary record sizes.
Restrictions
The ASCII/EBCDIC conversion tables are taken from the 256-character standard in the Communications of the ACM, (R)November, 1968.
The ibm conversion corresponds to certain IBM print train conventions.
One must specify ``conv=noerror,sync'' when copying raw disks with bad sectors to ensure that dd stays synchronized.
On SCSI tape devices when reading a multi-volume tape set the command will exit normally upon hitting EOT on any volume rather than auto-
matically unloading the volume and prompting for the next volume as is normal. The user should load the next volume and issue the command
anew.
Diagnostics
f+p records in(out): numbers of full and partial records read(written)
See Alsocp(1), tr(1), nbuf(4)dd(1)