Hmm, dd is some kind of the shell user's swiss army knife and sometimes even the swiss army chainsaw ;-) and such tools need a bit of learning to use them properly. actually, this "swiss" metapher is not fair, dd is more similar to a precision tool.
You read about these fake SD cards or USB sticks on sale, where the controller asserts a much larger memory size than the card actually has? You can check such cards with dd, e.g.:
for i in $(seq 1 9999) ; do echo -n "$i "; echo "Record Number $i" | \
dd ibs=1K count=1 obs=256K seek=$[i-1] cbs=4K copy=block,sync of=/dev/sdX
if [[ $? > 0 ]] ; then break ; fi
done
This writes numbered and blank padded blocks (due to the cbs=...) at the start of every 256K block of a device. Adjust your parameters to taste and match the purported size of your card or stick and later retrieve the first block to see if it contains "Record Number 1" or some other number due to wrapping around during writes. (and sure, ibs and count can be removed in the above example, I added them to demonstrate useful options in case the input isn't a simple echo command)
Anyway, I'd like to see how the author would handle all those blocking & unblocking, conversion, padding or sync requests available with dd with his head/tail approach. And what about the syntax? OK it was a a joke due to IBM's JCL, but I had to learn infix, postfix and even postfix notation for math (i.e. 5+3, 9! or f(x,y) and integrals and ...) which sometimes too looks like JCL? And have to remember if I need to use -c or -m even for simple tools like wc.
You read about these fake SD cards or USB sticks on sale, where the controller asserts a much larger memory size than the card actually has? You can check such cards with dd, e.g.:
This writes numbered and blank padded blocks (due to the cbs=...) at the start of every 256K block of a device. Adjust your parameters to taste and match the purported size of your card or stick and later retrieve the first block to see if it contains "Record Number 1" or some other number due to wrapping around during writes. (and sure, ibs and count can be removed in the above example, I added them to demonstrate useful options in case the input isn't a simple echo command)Anyway, I'd like to see how the author would handle all those blocking & unblocking, conversion, padding or sync requests available with dd with his head/tail approach. And what about the syntax? OK it was a a joke due to IBM's JCL, but I had to learn infix, postfix and even postfix notation for math (i.e. 5+3, 9! or f(x,y) and integrals and ...) which sometimes too looks like JCL? And have to remember if I need to use -c or -m even for simple tools like wc.
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