First install the Nix package manager and then enable Flakes. Alternatively, check out the Determinate Systems Installer for an out of the box experience. See nix.dev for more help with Nix.
To get a shell with ExaCA temporarily installed, run:
$ nix shell github:LLNL/ExaCA
# ExaCA now available
$ ExaCA --help
To install this permanently, run:
$ nix profile install github:LLNL/ExaCA?dir=envs/nix
To get a specific release, use:
$ nix shell github:LLNL/ExaCA/<tag>?dir=envs/nix
To build from a working copy use nix develop and run CMake manually:
$ nix develop
$ cmake -B build
$ cmake --build build
See the main README for more details on building ExaCA.