dd

dd [option=value]

Make a copy of an input file (if=), or standard input if no named input file, using the specified conditions, and send the results to the output file (or standard output if of is not specified). Any number of options can be supplied, although if and of are the most common and are usually specified first. Because dd can handle arbitrary block sizes, it is useful when converting between raw physical devices.

Options

bs=n

Set input and output block size to n bytes; this option supersedes ibs and obs.

cbs=n

Set the size of the conversion buffer (logical record length) to n bytes. Use only if the conversion flag is ascii, asciib, ebcdic, ebcdicb, ibm, ibmb, block, or unblock.

conv=flags

Convert the input according to one or more (comma-separated) flags listed below. The first six flags are mutually exclusive. The next two are mutually exclusive with each other, as are the following two.

ascii	EBCDIC to ASCII.
asciib	EBCDIC to ASCII, using BSD-compatible conversions. Solaris only.
ebcdic	ASCII to EBCDIC.
ebcdicb	ASCII to EBCDIC, using BSD-compatible conversions. Solaris only.
ibm	ASCII to EBCDIC with IBM conventions.
ibmb	ASCII to EBCDIC with IBM conventions, using BSD-compatible conversions. Solaris only.
block	Variable-length records (i.e., those terminated by a newline) to fixed-length records.
unblock	Fixed-length records to variable-length.
lcase	Uppercase to lowercase.
ucase	Lowercase to uppercase.
noerror	Continue processing when errors occur (up to five in a row).
notrunc	Do not truncate the output file. This preserves blocks in the output file that this invocation of dd did not write. Solaris only.
swab	Swap all pairs of bytes.
sync	Pad input blocks to ibs.

count=n

Copy only n input blocks.

files=n

Copy n input files (e.g., from magnetic tape), then quit.

ibs=n

Set input block size to n bytes (default is 512).

if=file

Read input from file (default is standard input).

obs=n

Set output block size to n bytes (default is 512).

of=file

Write output to file (default is standard output).

iseek=n

Seek n blocks from start of input file (like skip but more efficient for disk file input).

oseek=n

Seek n blocks from start of output file.

seek=n

Same as oseek (retained for compatibility).

skip=n

Skip n input blocks; useful with magnetic tape.

You can multiply size values (n) by a factor of 1024, 512, or 2 by appending the letters k, b, or w, respectively. You can use the letter x as a multiplication operator between two numbers.

Examples

Convert an input file to all lowercase:

dd if=caps_file of=small_file conv=lcase

Retrieve variable-length data; write it as fixed-length to out:

data_retrieval_cmd | dd of=out conv=sync,block