You want to attach a digital signature to a text file to verify its authenticity, leaving the file human-readable.
$ gpg --clearsign myfile
You'll be prompted for your passphrase.
If your original file has this content:
then the signed file will look something like this:
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hello world! -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.6 (GNU/Linux) Comment: For info see http://www.gnupg.org iD8DBQE9WFNU5U0ZSgD1tx8RAkAmAJ4wWTKWSy6C30raF2RWfQ6Eh8ZXAQCePUW3 N9JVeHSgYuSFu6XPLKW+2XU= =5XaU -----END PGP SIGNATURE-----
Anyone who has your public key can check the signature in this file using gpg, thereby confirming that the file is from you. [Recipe 7.15]