Bash: substitute some bytes in a binary file

Question

I have a binary file zero.bin which contains 10 bytes of 0x00, and a data file data.bin which contains 5 bytes of 0x01. I want to substitute the first 5 bytes of the zero.bin with data.bin. I have tried

dd if=data.bin of=zero.bin bs=1 count=5

but, the zero.bin is truncated, finally it becomes 5 bytes of 0x01. I want to keep the tailing 5 bytes of 0x00.

score 9 · Accepted Answer · answered Apr 26 '12 at 05:22

9

No problem, just add conv=notrunc:

dd if=data.bin of=zero.bin bs=1 count=5 conv=notrunc

answered Apr 26 '12 at 05:22

Gordon Davisson

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score 1 · Answer 2 · answered Apr 26 '12 at 01:58

1

You have half of the solution; do that into a temporary file tmp.bin instead of zero.bin, then

dd if=zero.bin bs=1 seek=5 skip=5 of=tmp.bin
mv zero.bin old.bin # paranoia
mv tmp.bin zero.bin

answered Apr 26 '12 at 01:58

geekosaur

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score 0 · Answer 3 · answered Apr 26 '12 at 02:05

0

Don't get stuck on using dd(1). There are other tools, eg:

(cat data.bin && tail -c +5 zero.bin) > updated.bin

answered Apr 26 '12 at 02:05

Jonathan

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Bash: substitute some bytes in a binary file

3 Answers3