How to grab an arbitrary chunk from a file on unix/linux [duplicate]

Answer 1

You can use tail -c+N to trim the leading N bytes from input, then you can use head -cM to output only the first M bytes from its input.

$ echo "hello world 1234567890" | tail -c+9 | head -c6
rld 12

So using your variables, it would probably be:

tail -c+$offset inputfile | head -c$datalength > outputfile

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Ah, didn't see it had to seek. Leaving this as CW.