gpg --clearsign

echo "test" | gpg --clearsign
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

test
gpg: signing failed: Inappropriate ioctl for device
gpg: [stdin]: clear-sign failed: Inappropriate ioctl for device

export GPG_TTY=$(tty)
echo $GPG_TTY

echo "test" | gpg --clearsign
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

test 
gpg: signing failed: No pinentry 
gpg: [stdin]: clear-sign failed: No pinentry

gpg --full-generate-key

See also

• pinentry
• GNU Privacy Guard (GPG), gpg, gpg-agent, gpg-connect-agent, gpg-suite, GPGAuth, gpg --help, ~/.gnupg/
• Serial, tty, minicom, screen, PuTTY (plink), getty, agetty, usb-devices, usbserial, PTY, pts, minicom, screen, RequestTTY, stty, virsh ttyconsole, stty sane, Unable to use a TTY, tty: