DD(1) 386BSD Reference Manual DD(1)
NAME
dd - Convert and copy a file.
SYNOPSIS
dd [operands ...]
DESCRIPTION
The dd utility copies the standard input to the standard output. Input
data is read and written in 512-byte blocks. If input reads are short,
input from multiple reads are aggregated to form the output block. When
finished, dd displays the number of complete and partial input and output
blocks and truncated input records to the standard error output.
The following operands are available:
bs=n Set both input and output block size, superseding the ibs and
obs operands. If no conversion values other than noerror,
notrunc or sync are specified, then each input block is copied
to the output as a single block without any aggregation of short
blocks.
cbs=n Set the conversion record size to n bytes. The conversion
record size is required by the record oriented conversion
values.
count=n Copy only n input blocks.
files=n Copy n input files before terminating. This operand is only
applicable when the input device is a tape.
ibs=n Set the input block size to n bytes instead of the default 512.
if=file Read input from file instead of the standard input.
obs=n Set the output block size to n bytes instead of the default 512.
of=file Write output to file instead of the standard output. Any
regular output file is truncated unless the notrunc conversion
value is specified. If an initial portion of the output file is
skipped (see the seek operand) the output file is truncated at
that point.
seek=n Seek n blocks from the beginning of the output before copying.
On non-tape devices, a lseek(2) operation is used. Otherwise,
existing blocks are read and the data discarded. If the user
does not have read permission for the tape, it is positioned
using the tape ioctl(2) function calls. If the seek operation
is past the end of file, space from the current end of file to
the specified offset is filled with blocks of NUL bytes.
skip=n Skip n blocks from the beginning of the input before copying.
On input which supports seeks, a lseek(2) operation is used.
Otherwise, input data is read and discarded. For pipes, the
correct number of bytes is read. For all other devices, the
correct number of blocks is read without distinguishing between
a partial or complete block being read.
conv= value[, value ...]
Where value is one of the symbols from the following list.
ascii, oldascii
The same as the unblock value except that characters
are translated from ECBDIC to ASCII before the records
are converted. (These values imply unblock if the
operand cbs is also specified.) There are two
conversion maps for ASCII. The value ascii specifies
the recommended one which is compatible with System V.
The value oldascii specifies the one used in historic
AT&T and pre-4.3BSD-Reno systems.
block Treats the input as a sequence of newline or end-of-
file terminated variable length records independent of
input and output block boundaries. Any trailing
newline character is discarded. Each input record is
converted to a fixed length output record where the
length is specified by the cbs operand. Input records
shorter than the conversion record size are padded with
spaces. Input records longer than the conversion
record size are truncated. The number of truncated
input records, if any, are reported to the standard
error at the completion of the copy.
ebcdic, ibm, oldebcdic, oldibm
The same as the block value except that characters are
translated from ASCII to EBCDIC after the records are
converted. (These values imply block if the operand
cbs is also specified.) There are four conversion maps
for EBCDIC. The value ebcdic specifies the recommended
one which is compatible with AT&T System V UNIX. The
value ibm is a slightly different mapping, which is
compatible with the AT&T System V UNIX ibm value. The
values oldebcdic and oldibm are maps used in historic
AT&T and pre-4.3BSD-Reno systems.
lcase Transform uppercase characters into lowercase
characters.
noerror Do not stop processing on an input error. When an
input error occurs, a diagnostic message followed by
the current input and output block counts will be
written to standard error in the same format as the
standard completion message. If the sync conversion is
also specified, any missing input data will be replaced
with NUL bytes (or with spaces if a block oriented
conversion value was specified) and processed as a
normal input buffer. If the sync conversion is not
specified, the input block is omitted from the output.
On input files which are not tapes or pipes, the file
offset will be positioned past the block in which the
error occurred using lseek(2).
notrunc Do not truncate the output file. This will preserve
any blocks in the output file not explicitly written by
dd. The notrunc value is not supported for tapes.
swab Swap every pair of input bytes. If an input buffer has
an odd number of bytes, the last byte will be ignored
during swapping.
sync Pad every input block to the input buffer size. Spaces
are used for pad bytes if a block oriented conversion
value is specified, otherwise NUL bytes are used.
ucase Transform lowercase characters into uppercase
characters.
unblock Treats the input as a sequence of fixed length records
independent of input and output block boundaries. The
length of the input records is specified by the cbs
operand. Any trailing space characters are discarded
and a newline character is appended.
Where sizes are specified, a decimal number of bytes is expected. If the
number ends with a ``b'', ``k'', ``m'' or ``w'', the number is multiplied
by 512, 1024 (1K), 1048576 (1M) or the number of bytes in an integer,
respectively. Two or more numbers may be separated by an ``x'' to
indicate a product.
When finished, dd displays the number of complete and partial input and
output blocks, truncated input records and odd-length byte-swapping
blocks to the standard error output. A partial input block is one where
less than the input block size was read. A partial output block is one
where less than the output block size was written. Partial output blocks
to tape devices are considered fatal errors. Otherwise, the rest of the
block will be written. Partial output blocks to character devices will
produce a warning message. A truncated input block is one where a
variable length record oriented conversion value was specified and the
input line was too long to fit in the conversion record or was not
newline terminated.
Normally, data resulting from input or conversion or both are aggregated
into output blocks of the specified size. After the end of input is
reached, any remaining output is written as a block. This means that the
final output block may be shorter than the output block size.
If dd receives a SIGINFO (see the ``status'' argument for stty(1))
signal, the current input and output block counts will be written to
standard error in the same format as the standard completion message. If
dd receives a SIGINT signal, the current input and output block counts
will be written to standard error in the same format as the standard
completion message and dd will exit.
The dd utility exits 0 on success and >0 if an error occurred.
SEE ALSO
cp(1), mt(1), tr(1)
STANDARDS
The dd utility is expected to be a superset of the IEEE Std1003.2
(``POSIX'') standard. The files operand and the ascii, ebcdic, ibm,
oldascii, oldebcdic and oldibm values are extensions to the POSIX
standard.
BSD Experimental August 7, 1991 3