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 over-
rides 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 pad-
ding 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 suc-
cessfully.
--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
NOTES
This page describes dd as found in the fileutils-3.16 pack-
age; 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.