HASH=$(...) fails silently if the wrong sha3sum is installed

[kstrauser]

Suppose you're on a Mac and you've run brew install sha3sum, giving you a sha3sum command that's incompatible with the expected one.

Then this line:

HASH=$(echo -n "$DATA_HEX" | xxd -r -p | (sha3sum -a Keccak256 -t || true) | sed 's/[^[:xdigit:]].*//')

writes

/opt/homebrew/bin/sha3sum: valid arguments for -a are 224 (default), 256, 384, and 512

to stderr and returns an empty value. Later on,

SIGNATURE_HEX=$(echo "$HASH" | xxd -r -p | openssl pkeyutl -sign -inkey "$ETH_KEY" | xxd -p -c 72)

will successfully sign an empty string.