DD
NAME
dd - convert and copy a file
SYNOPSIS
dd
[--help] [--version]
[if=file]
[of=file]
[ibs=bytes]
[obs=bytes]
[bs=bytes]
[cbs=bytes]
[skip=blocks]
[seek=blocks]
[count=blocks]
[conv={ascii, ebcdic, ibm, block, unblock, lcase, ucase, swab, noerror, notrunc, sync}]
DESCRIPTION
dd
copies a file (from standard input to standard output, by
default) using specific input and output blocksizes,
while optionally performing conversions on it.
It reads the input one block at a time, using the specified input
block size (the default is 512 bytes).
If the
bs=bytes
option was given, and no conversion other than
sync, noerror, or notrunc
was specified, it writes the amount of data read (which could be smaller
than what was requested) in a separate output block. This output block
has precisely the same length as was read unless the
sync
conversion was specified, in which case the data is padded with NULs
(or spaces, see below).
Otherwise, the input, read one block at a time, is processed
and the resulting output is collected and written in blocks
of the specified output block size. The final output block
may be shorter.
The numeric-valued options below (bytes and blocks) can be followed
by a multiplier: `k'=1024, `b'=512, `w'=2, `c'=1
(`w' and `c' are GNU extensions; `w' should never be used -
it means 2 in System V and 4 in 4.2BSD).
Two or more of such numeric expressions can be multiplied
by putting `x' in between.
OPTIONS
- if=file
-
Read from
file
instead of standard input.
- of=file
-
Write to
file
instead of standard output. Unless
conv=notrunc
is given,
dd
truncates
file
to zero bytes (or the size specified with
seek=).
- ibs=bytes
-
Read
bytes
bytes at a time. The default is 512.
- obs=bytes
-
Write
bytes
bytes at a time. The default is 512.
- bs=bytes
-
Both read and write
bytes
bytes at a time. This overrides
ibs
and
obs.
(And setting
bs
is not equivalent with setting both
ibs
and
obs
to this same value, at least when no conversion other than
sync,
noerror
and
notrunc
is specified, since it stipulates that each input block
shall be copied to the output as a single block
without aggregating short blocks.)
- cbs=bytes
-
Specify the conversion block size for
block
and
unblock.
- skip=blocks
-
Skip
blocks
ibs-byte
blocks in the input file before copying.
- seek=blocks
-
Skip
blocks
obs-byte
blocks in the output file before copying.
- count=blocks
-
Copy
blocks
ibs-byte
blocks from the input file, instead of everything
until the end of the file.
- conv=CONVERSION[,CONVERSION]...
-
Convert the file as specified by the
CONVERSION
argument(s). (No spaces around any comma(s).)
-
Conversions:
- ascii
-
Convert EBCDIC to ASCII.
- ebcdic
-
Convert ASCII to EBCDIC.
- ibm
-
Convert ASCII to alternate EBCDIC.
- block
-
For each line in the input, output
cbs
bytes, replacing the input newline with a space and padding
with spaces as necessary.
- unblock
-
Replace trailing spaces in each
cbs-sized
input block with a newline.
- lcase
-
Change uppercase letters to lowercase.
- ucase
-
Change lowercase letters to uppercase.
- swab
-
Swap every pair of input bytes.
GNU
dd,
unlike others, works when an odd number of bytes are read - the last
byte is simply copied (since there is nothing to swap it with).
- noerror
-
Continue after read errors.
- notrunc
-
Do not truncate the output file.
- sync
-
Pad every input block to size of
ibs
with trailing zero bytes.
GNU STANDARD OPTIONS
- --help
-
Print a usage message on standard output and exit successfully.
- --version
-
Print version information on standard output, then exit successfully.
- --
-
Terminate option list.
ENVIRONMENT
The variables LANG, LC_ALL, LC_CTYPE and LC_MESSAGES have the
usual meaning.
CONFORMING TO
POSIX 1003.2
SEE ALSO
cp
slice
binedit
NOTES
This page describes
dd
as found in the fileutils-3.16 package;
other versions may differ slightly. Mail corrections and additions to
aeb@cwi.nl and aw@mail1.bet1.puv.fi and ragnar@lightside.ddns.org .
Report bugs in the program to fileutils-bugs@gnu.ai.mit.edu.