OpenSSL

show contents of a PEM encoded certificate: openssl x509 -in <cert>.pem -text
extract public key from certificate: openssl x509 -pubkey -noout -in cert.pem > pubkey.pem

ECDSA

list EC curves: openssl ecparam -list_curves
generate ECDSA key: openssl ecparam -name brainpoolP256r1 -genkey -noout -out <keyfile-priv.pem>
write public key: openssl ec -in <keyfile-priv.pem> -pubout -out <keyfile-pub.pem>
show ECDSA key: openssl ec -in <keyfile-priv.pem> -text -noout
show digest: openssl dgst -sha256 -sign <keyfile-priv.pem> -hex ectest.txt
sign file: openssl dgst -sha256 -sign <keyfile-priv.pem> ectest.txt > ecdsa256sig.bin
verify file: openssl dgst -sha256 -verify <keyfile-pub.pem> -signature ecdsa256sig.bin ectest.txt
SHA-256 Digest: sha256sum ectest.txt > sha256.hex; xxd -r -p sha256.hex > sha256.bin