How do I extract a single chunk of bytes from within a file?

Question

On a Linux desktop (RHEL4) I want to extract a range of bytes (typically less than 1000) from within a large file (>1 Gig). I know the offset into the file and the size of t

Answer 1

Try dd:

dd skip=102567 count=253 if=input.binary of=output.binary bs=1

Answer 2

head -c + tail -c

Not sure how it compare to dd in efficiency, but it is fun:

printf "123456789" | tail -c+2 | head -c3

picks 3 bytes, starting at the 2nd one:

234

See also: https://stackoverflow.com/a/1272995/895245

Answer 3

The dd command can do all of this. Look at the seek and/or skip parameters as part of the call.

Answer 4

This is an old question, but I'd like to add another version of the dd command that is better-suited for large chunks of bytes:

dd if=input.binary of=output.binary skip=$offset count=$bytes iflag=skip_bytes,count_bytes 

where $offset and $bytes are numbers in byte units.

The difference with Thomas's accepted answer is that bs=1 does not appear here. bs=1 produces the input and output block size to be 1 byte, which makes it terribly slow when the number of bytes to extract is large.

Answer 5

Even faster

dd bs=<req len> count=1 skip=<req offset> if=input.binary of=output.binary