# encryption
gpg --batch --yes --passphrase "your-password" --symmetric filename.ext
# OR read password from file
cat password.txt | gpg --batch --yes --passphrase-fd 0 --symmetric filename.ext

# decryption
gpg --batch --yes --passphrase "your-password" -o filename.ext --decrypt filename.ext.gpg
# OR read password from file
cat password.txt | gpg --batch --yes --passphrase-fd 0 -o filename.ext --decrypt filename.ext.gpg