dd
dd options
Make a copy of an input file (if) 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 overrides 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, ebcdic, ibm, block, or unblock.
conv=flags
Convert the input according to one or more (comma-separated) flags listed next. The first five flags are mutually exclusive.
ascii
EBCDIC to ASCII.
ebcdic
ASCII to EBCDIC.
ibm
ASCII to EBCDIC with IBM conventions.
block
Variable-length records (i.e., those terminated by a newline) to fixed-length records.
unblock
Fixed-length records to variable-length records.
lcase
Uppercase to lowercase.
ucase
Lowercase to uppercase.
noerror
Continue processing after read errors.
notrunc
Don't truncate output file.
swab
Swap each pair of input bytes.
sync
Pad input blocks to ibs with trailing zeros.
count=n
Copy only n input blocks.
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).
seek=n
Skip n output-sized blocks from start of output file.
skip=n
Skip n input-sized blocks from start of input file.
--help
Print help message and then exit.
--version
Print the version number and then exit.
You can multiply size values (n) by a factor of 1024, 512, or 2 by appending the letter 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 and write it as fixed-length to out:
[data_retrieval_cmd] | dd of=out conv=sync,block
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