Hash

md5sum [file]	MD5 hash.
sha1sum [file]	SHA-1 hash.
sha256sum [file]	SHA-256 hash.
sha512sum [file]	SHA-512 hash.
sha224sum [file]	SHA-224 hash.
sha384sum [file]	SHA-384 hash.
cksum [file]	CRC checksum along with the byte size.
openssl md5 [file]	MD5 hash using OpenSSL.
openssl sha1 [file]	SHA-1 hash using OpenSSL.
openssl dgst -sha256 [file]	SHA-256 hash using OpenSSL.
openssl dgst -sha512 [file]	SHA-512 hash using OpenSSL.

Compare two files by their SHA256 hash: If the output is 1, it indicates that the two files have the same SHA-256 hash.

This is complete overkill...

echo "$(sha256sum file1 | cut -d' ' -f1) $(sha256sum file2 | cut -d' ' -f1)" | tr ' ' '\n' | uniq | wc -l