OS Specific Build Step

[Anti-Distinctlyminty]

Hi,
I'm using Rez for the first time and I'm trying to setup a simple package (using to see if I can get my head around it all. I'm being faced with a missing lib on Rocky Linux 9, so I thought to myself that I would add a step during the build command to download and copy the shared lib to the install. I cannot find an elegant way to do this, which I suspect means that I do not understand how Rez works and I would be grateful if someone could illustrate what I should be doing.

Here are my package.py and build.py files

# package.py

name = "gaffer"
version = "1.0.4"
has_plugins = True

variants = [
    ["platform-linux", "arch-x86_64", "os-rocky-9.0"]
]

build_command = "python {root}/build.py {install}"

def commands():
    env.PATH.append("{root}/gaffer-1.0.4.0-linux-python3/bin")

# build.py
import os
import sys
from pathlib import Path
from subprocess import Popen


def build(source_path, build_path, install_path, targets):

    if "install" in targets:

        # Do regular install suff

        # This seems very hacky and wrong!
        for packageName in os.environ["REZ_USED_RESOLVE"].split(" "):
            if packageName.startswith("os-rocky-9."):
                print(f"Running {packageName}")
                # Do Rocky 9 specific stuff
            

if __name__ == "__main__":
    build(
        source_path=os.environ["REZ_BUILD_SOURCE_PATH"],
        build_path=os.environ["REZ_BUILD_PATH"],
        install_path=os.environ["REZ_BUILD_INSTALL_PATH"],
        targets=sys.argv[1:],
    )

So, what would be the "proper" way to do this? I have searched but cannot find out how to make use of Rez's features inside of the build function with the exception of reading some environment variables.