dd(1)dd(1)NAMEdd - convert, reblock, translate, and copy a (tape) file
SYNOPSIS
[optionvalue] ...
DESCRIPTION
copies the specified input file to the specified output file with pos‐
sible 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 partial
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, supersed‐
ing
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 fol‐
lowing list.
Convert EBCDIC to ASCII.
Convert ASCII to EBCDIC.
Convert ASCII to EBCDIC using an alternate con‐
version 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 char‐
acter is removed, and space
characters are used to fill the
block to size Lines that are
longer than are truncated; the
number of truncated lines
(records) is reported (see
below).
The values are mutually exclu‐
sive.
Convert fixed-length input records to variable-
length records.
For each input record, bytes
are read, trailing space char‐
acters are deleted, and a new‐
line character is appended.
Map upper-case input characters to the corre‐
sponding lower-case characters.
The values are mutually exclu‐
sive.
Map lower-case input characters to the corre‐
sponding 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. Num‐
bers can be specified using the forms:
n for n bytes
for n Kbytes (n × 1024),
for n blocks (n × 512), or
for n words (n × 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 con‐
version 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 envi‐
ronment variables beginning with
The variable determines the locale for the interpretation of sequences
of bytes of text data as characters (single-byte/multi-byte characters,
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
writing in arbitrary block sizes.
WARNINGS
Some devices, such as 1/2-inch magnetic tapes, are incapable of seek‐
ing. 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 ALSOcp(1), mt(1), tr(1), disk(7), mt(7).
STANDARDS CONFORMANCEdd(1)
