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 - convert, reblock, translate, and copy a (tape) file
SYNOPSIS
[optionvalue] ...
DESCRIPTION
copies the specified input file to the specified output file with possible conversions. The standard input and output are used by default.
Input and output block size can be specified to take advantage of raw physical I/O. Upon completion, reports the number of whole and par-
tial input and output records.
Options
recognizes the following pairs:
Input file name; default is standard input.
Output file name; default is standard output.
The output file is created using the same owner and group used by
Input block size is
n bytes; default is 512.
Output block size is
n bytes; default is 512.
Set both input and output block size to the same size, superseding
and This option is particularly efficient if no conversion is specified, because no in-core copy is necessary.
Conversion buffer size is
n bytes.
Skip n input blocks before starting copy.
Skip n input blocks before starting copy. (This is an alias for the option.)
Skip n blocks from beginning of output file before copying.
Skip n blocks from beginning of output file before copying. (This is an alias for the option.)
Copy only n input blocks.
Copy and concatenate
n input files. This option should be used only when the input file is a magnetic tape device.
Where values are comma-separated symbols from the following list.
Convert EBCDIC to ASCII.
Convert ASCII to EBCDIC.
Convert ASCII to EBCDIC using an alternate conversion table.
The and values are mutually exclusive.
Convert each newline-terminated or end-of-file-terminated input record
to a record with a fixed length specified by Any newline character is removed, and space characters
are used to fill the block to size Lines that are longer than are truncated; the number of trun-
cated lines (records) is reported (see below).
The values are mutually exclusive.
Convert fixed-length input records to variable-length records.
For each input record, bytes are read, trailing space characters are deleted, and a newline charac-
ter is appended.
Map upper-case input characters to the corresponding lower-case characters.
The values are mutually exclusive.
Map lower-case input characters to the corresponding upper-case characters.
Swap every pair of input bytes.
Do not stop processing on an input error.
If the conversion symbol is also specified, missing input is replaced with null bytes and processed
normally; otherwise, the input block is omitted from the output.
Do not truncate existing output file.
Blocks in the output file not overwritten by this invocation of are preserved.
Pad every input block to size
If is also specified, pad with space characters; otherwise, pad with null bytes.
Where sizes are required, n indicates a numerical value in bytes. Numbers can be specified using the forms:
n for n bytes
for n Kbytes (n x 1024),
for n blocks (n x 512), or
for n words (n x 2).
To indicate a product, use to separate number pairs.
The option is used when or conversion is specified. In case of cbs characters are placed into the conversion buffer, converted to ASCII,
trailing blanks are trimmed, and a newline is added before sending the line to the output. In case of ASCII characters are read into the
conversion buffer, converted to EBCDIC, and blanks are added to make up an output block of size cbs.
EXTERNAL INFLUENCES
International Code Set Support
Single- and multi-byte character code sets are supported.
Environment Variables
The following environment variables affect execution of
determines the locale when and a corresponding variable (beginning with do not specify a locale.
determines the locale used to override any values set by or any environment variables beginning with
The variable determines the locale for the interpretation of sequences of bytes of text data as characters (single-byte/multi-byte charac-
ters, upper-case/lower-case characters).
The variable determines the language in which messages are written.
RETURN VALUE
Exit values are:
Successful completion.
Error condition occurred.
DIAGNOSTICS
Upon completion, reports the number of input and output records:
Number of full and partial blocks read.
Number of full and partial blocks written.
When is specified and there is at least one truncated block, the number of truncated records is also reported:
EXAMPLES
Read an EBCDIC tape blocked ten 80-byte EBCDIC card images per block into an ASCII file named
Note the use of the raw magnetic tape device file. is especially suited to I/O on raw physical devices because it allows reading and writ-
ing in arbitrary block sizes.
WARNINGS
Some devices, such as 1/2-inch magnetic tapes, are incapable of seeking. Such devices may be positioned prior to running by using mt(1) or
some other appropriate command. The options do work for such devices. However, skipping blocks using these options is slow on devices
that cannot seek, since the blocks must actually be read to get to the desired position on the tape.
ASCII and EBCDIC conversion tables are taken from the 256-character ACM standard, Nov, 1968. The conversion, while less widely accepted as
a standard, corresponds better to certain IBM print train conventions. There is no universal solution.
Newline characters are inserted only on conversion to ASCII; padding is done only on conversion to EBCDIC. These should be separate
options.
If or refers to a raw disk, should always be a multiple of the sector size of the disk. By default, is 512 bytes. If the sector size of
the disk is different from 512 bytes, should be specified using a multiple of sector size. The character special (raw) device file should
always be used for devices.
It is entirely up to the user to insure there is enough room in the destination file, file system and/or device to contain the output since
cannot pre-determine the required space after conversion.
SEE ALSO cp(1), mt(1), tr(1), disk(7), mt(7).
STANDARDS CONFORMANCE dd(1)