GNU Privacy Guard 2. See gpg for GNU Privacy Guard 1.

# To list imported keys:
gpg2 --list-keys

# To encrypt a specified file for a specified recipient, writing the output to a new file with '.gpg' appended:
gpg2 --encrypt --recipient <alice@example.com> <path/to/doc.txt>

# To encrypt a specified file with only a passphrase, writing the output to a new file with '.gpg' appended:
gpg2 --symmetric <path/to/doc.txt>

# To decrypt a specified file, writing the result to the standard output:
gpg2 --decrypt <path/to/doc.txt.gpg>

# To import a public key:
gpg2 --import <path/to/public_key.gpg>

# To export the public key of a specified email address to the standard output:
gpg2 --export --armor <alice@example.com>

# To export the private key with a specified email address to the standard output:
gpg2 --export-secret-keys --armor <alice@example.com>