How do I get the exact values of the near and far planes in clip space, both in a shader and in C#?

I'm playing around with a plugin idea that manually does something similar to shadow-maps, and I need to know the values for the near and far Z bounds in clip space -- depending on the graphics API, they could be 0 to 1, -1 to 1, or possibly 1 to 0 (and maybe even 1 to -1?). Unity docs mention the macros UNITY_NEAR_CLIP_VALUE and UNITY_REVERSED_Z, but there are two problems:

1. It doesn't give a concrete example of actually defining the near/far values in a fully platform-agnostic way.

2. It only explains how to find these values in a shader, not in a C# script.

If you can answer either of these two issues, I'd appreciate it!

I have an idea for how to get the near/far values in a shader, but there's no way to know if it's platform-agnostic without testing every concievable platform, which is unfeasible:

 #if defined(UNITY_REVERSED_Z)
     const float nearPlane = 1.0,
                 farPlane = UNITY_NEAR_CLIP_VALUE;
 #else
     const float nearPlane = UNITY_NEAR_CLIP_VALUE,
                 farPlane = 1.0;
 #endif