kristianf@ares ~ $ export GNUPGHOME=$(mktemp -d)
kristianf@ares ~ $ gpg --quick-gen-key 'test user <test@example.org>'
gpg: keybox '/tmp/tmp.ZfFB9zG2ux/pubring.kbx' created
About to create a key for:
    "test user <test@example.org>"

Continue? (Y/n) y
We need to generate a lot of random bytes. It is a good idea to perform
some other action (type on the keyboard, move the mouse, utilize the
disks) during the prime generation; this gives the random number
generator a better chance to gain enough entropy.
We need to generate a lot of random bytes. It is a good idea to perform
some other action (type on the keyboard, move the mouse, utilize the
disks) during the prime generation; this gives the random number
generator a better chance to gain enough entropy.
gpg: /tmp/tmp.ZfFB9zG2ux/trustdb.gpg: trustdb created
gpg: key 256413809A53C375 marked as ultimately trusted
gpg: directory '/tmp/tmp.ZfFB9zG2ux/openpgp-revocs.d' created
gpg: revocation certificate stored as '/tmp/tmp.ZfFB9zG2ux/openpgp-revocs.d/6934E3E16FE5DB2A93B4DB32256413809A53C375.rev'
public and secret key created and signed.

pub   rsa2048 2017-08-18 [SC] [expires: 2019-08-18]
      6934E3E16FE5DB2A93B4DB32256413809A53C375
uid                      test user <test@example.org>
sub   rsa2048 2017-08-18 [E]

kristianf@ares ~ $ gpg --batch --pinentry-mode loopback --password '' --clearsign <<<"TEST"
gpg: invalid option "--password"
kristianf@ares ~ $ gpg --batch --pinentry-mode loopback --passphrase '' --clearsign <<<"TEST"
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

TEST
-----BEGIN PGP SIGNATURE-----

iQEzBAEBCAAdFiEEaTTj4W/l2yqTtNsyJWQTgJpTw3UFAlmW5eMACgkQJWQTgJpT
w3VPQQf+JX/ogyH96F1TExApzidJq9c9DQKuhI/3UAyIoY6qPwqaJyG219tFlJL2
peChUxoz2Duo5x6CW+akXCYDIjs3vFDcQge2MP7xFuohODktkllFefhaLhDlG+0A
vv7tt4SXq2uiqM3qBHZTaVol9XeWSex4oSco8KtOcQBX2ed8THFKBYzdw43tBTxS
LYBha7D8qpTmKqfElZZDaURLuAc59N1LVFbcO3B7u8VT0H33Bm6kmK+rgUyTscSl
6dSYXIyZhyDULJ+PwLd2AXBAaTo783ldFSClnVuqjapSAKlql0pzhahQ4K2Gy8ai
+KSfjrKTLM3VJxxyJeP48Ipm80syHw==
=Lbjb
-----END PGP SIGNATURE-----

$ gpg --batch --clearsign <<<"TEST"
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

TEST
-----BEGIN PGP SIGNATURE-----

iQEzBAEBCAAdFiEEaTTj4W/l2yqTtNsyJWQTgJpTw3UFAlmW5isACgkQJWQTgJpT
w3UTjQf/Stq/OoI4ZtFrwrcaXVFgbwZCUlRF82Hov2kYUihhOHrHPnGtCRvoh7uH
knsHOUR4kj5tMJ6IyEC8RTVJilQ8bFosv3CltMHk+zFx4PtfZYdIlo27HYsBeQv/
c+q5VHjDFbi9BY249Ff5/oAGVZNIK7FsDgIIMyXLDzS2ofh01lVBFFt0Q7kGyyVt
bYdTv5I7d9WHwz+/oL3HJnP5IPqbJkCaTh0eyxNNBdd096L6QKHbEHMZhtfcD6g8
OahONElp+VyuOVBAGFSsQrsfTJv5Q2h3uv5KIMC/sgaFcQCNN0gb1z1N7dweBnrL
9FfWd4AK00RzBQkq3S5A7ouFX4ZcQg==
=xatx
-----END PGP SIGNATURE-----

pkill -9 gpg-agent
$ gpg --batch --pinentry-mode loopback --passphrase '' --clearsign <<<"TEST"
gpg: no default secret key: No public key
gpg: [stdin]: clear-sign failed: No public key

$ gpg --batch --pinentry-mode loopback --passphrase '' -u test --clearsign <<<"TEST"
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

TEST
-----BEGIN PGP SIGNATURE-----

iQFFBAEBCAAvFiEEaTTj4W/l2yqTtNsyJWQTgJpTw3UFAlmW5nMRHHRlc3RAZXhh
bXBsZS5vcmcACgkQJWQTgJpTw3U25gf/Sini9QZdhjaItxmYT3rrxvaQKZJD3iNP
k2Q/qUikZq4NRHHCcZmptQlr5bBLgxRmu+m0aLWMiVzOH1StFXmo8iPCgKZYLucM
OHbglQBNZJZ46BDjjWEjZ6RSYdIMmkqLwkIIb7JN91+8BbqF8DlkAayyx38nEdB4
UPdVWu3ygtfu8rbJ4K8DWA9l7zegTCm2I+Izd84RGSbFSsm8YvsijgGXpy2g4cfB
P7a3sZzKQDRALDOLRp3rMxCCy7hcwhNAhW3Urj/cpsee0gZG18XVBRbuqczlzidZ
6hgAIkfAh6fZRKMgcn4MO4yzmk2SaniTILS9dUM2IP4A+OzAJ5AdPQ==
=5Jb9
-----END PGP SIGNATURE-----