Calculate or check cryptographic SHA checksums.

# To calculate the SHA1 checksum for a file:
shasum filename

# To calculate the SHA256 checksum for a file:
shasum --algorithm 256 filename

# To calculate the SHA512 checksum for multiple files:
shasum --algorithm 512 filename1 filename2

# To check a file with a list of sums against the directory's files:
shasum --check list_file

# To calculate the SHA1 checksum from stdin:
somecommand | shasum