File and Directory Commands dd - convert and copy a file
RTEMS Shell User's Guide
3.2.18: dd - convert and copy a file
SYNOPSYS:
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 operation is used. Otherwise, existing
blocks are read and the data discarded. 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 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.
progress=n
Switch on display of progress if n is set to any non-zero value. This
will cause a ``.'' to be printed (to the standard error output) for
every n full or partial blocks written to the output file.
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 EBCDIC 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 recom-
mended one which is compatible with AT&T System V UNIX. 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
output 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 the standard error output 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.
osync
Pad the final output block to the full output block size. If the
input file is not a multiple of the output block size after
conversion, this conversion forces the final output block to be the
same size as preceding blocks for use on devices that require
regularly sized blocks to be written. This option is incompatible
with use of the bs=n block size specification.
sparse
If one or more non-final output blocks would consist solely of NUL
bytes, try to seek the output file by the required space instead of
filling them with NULs. This results in a sparse file on some file
systems.
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. Two
or more numbers may be separated by an ``x'' to indicate a product.
Each number may have one of the following optional suffixes:
b
Block; multiply by 512
k
Kibi; multiply by 1024 (1 KiB)
m
Mebi; multiply by 1048576 (1 MiB)
g
Gibi; multiply by 1073741824 (1 GiB)
t
Tebi; multiply by 1099511627776 (1 TiB)
w
Word; multiply by the number of bytes in an integer
When finished, dd displays the number of complete and partial input
and output blocks, truncated input records and odd-length
byte-swapping ritten. 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.
EXIT STATUS:
This command returns 0 on success and non-zero if an error is encountered.
NOTES:
NONE
EXAMPLES:
The following is an example of how to use dd:
SHLL [/] $ dd if=/nfs/boot-image of=/dev/hda1
CONFIGURATION:
This command is included in the default shell command set. When
building a custom command set, define
CONFIGURE_SHELL_COMMAND_DD to have this command included.
This command can be excluded from the shell command set by defining
CONFIGURE_SHELL_NO_COMMAND_DD when all shell commands have been
configured.
PROGRAMMING INFORMATION:
The dd command is implemented by a C language function which
has the following prototype:
int rtems_shell_rtems_main_dd(
int argc,
char **argv
);
The configuration structure for the dd has the following
prototype:
RTEMS Shell User's Guide