This is a simple shell script that integrates suckless' dmenu with GnuPG as an alternative pinentry method.
To install this, do a git clone https://github.com/drincoxyz/pinentry-dmenu, configure config.mk for your system and run sudo make install. Similarly, to uninstall run sudo make uninstall.
There's also an AUR package available, which is recommended for Arch users. To install it, do a git clone https://aur.archlinux.org/pinentry-dmenu-inco.git and run makepkg -si, or use an AUR wrapper like yay and simply run yay -S pinentry-dmenu-inco as a non-root user.
Note that the pinentry-dmenu AUR package is not related to this project. That's another alternative that does more or less the same thing, but it builds its own dmenu binary with the password patch applied automatically. This project is much simpler, as it uses the first dmenu binary it finds on the system.
Firstly, you will need a dmenu build with the password patch applied, otherwise dmenu will not show up when used as the pinentry program.
Then, to use dmenu as the pinentry program for GnuPG, configure ~/.gnupg/gpg-agent.conf to use the full path of the pinentry-dmenu script:
pinentry-program /usr/bin/pinentry-dmenu
The full path will depend on the PREFIX used in config.mk. The above example would apply to users who installed the AUR package, but by installing it with make with the default PREFIX installs it to /usr/local/bin/pinentry-dmenu.