问题
Im writing a script to change the UUID of an NTFS partition (AFAIK, there is none). That means writing 8 bytes from 0x48 to 0x4F (72-79 decimal) of /dev/sdaX (X being the # of my partition).
If I wanted to change it to a random UUID, I could use this:
dd if=/dev/urandom of=/dev/sdaX bs=8 count=1 seek=9 conv=notrunc
Or I could change /dev/urandom to /dev/sdaY to clone the UUID from another partition.
But... what if I want to craft a personalized UUID? I already have it stored (and regex-checked) in a $UUID variable in hexadecimal string format (16 chars), like this:
UUID="2AE2C85D31835048"
I was thinking about this approach:
echo "$UUID" | xxd -r -p | dd of=/dev/sdaX ...
This is just a scratch... im not sure about the exact options to make it work. My question is:
- Is the
echo $var | xxd -r | ddreally the best approach? - What would be the exact command and options to make it work?
As for the answers, Im also looking for:
- An explanation of all the options used, and what they do.
- If possible, an alternative command to test it in a file and/or screen before changing the partition.
I already have an 100-byte dump file called ntfs.bin that i can use for tests and check results using
xxd ntfs.bin
So any solution that provides me a way to check results using xxd in screen so i can compare with original ntfs.bin file would be highly appreciated.
Thanks!
回答1:
Try:
UUID="2AE2C85D31835048"
echo "$UUID" | xxd -r -p | wc -c
echo "$UUID" | xxd -r -p | dd of=file obs=1 oseek=72 conv=block,notrunc cbs=8
回答2:
See here:
Replace chars in file by index
# start at char 20, replace the next 11 chars with '#'
echo '###########' | dd of=FILENAME seek=20 bs=1 count=11 conv=notrunc
来源：https://stackoverflow.com/questions/5196096/bash-scripting-how-to-patch-files-write-a-given-string-in-a-given-position-of