Setting Environment Variables for Child Process🔗

Setting environment variables for the current process is less common in pure Lean code. Usually, you set environment variables when spawning a new child process to configure its environment.

When using IO.Process.spawn, you can pass an env array to specify variables for the new process:

def runWithCustomEnv : IO Unit := do
  let child ← IO.Process.spawn {
    cmd := "printenv",
    args := #["MY_VAR"],
    env := #[("MY_VAR", "1234")]
  }
  let exitCode ← child.wait
  IO.println s!"Process exited with code: {exitCode}"

This ensures that MY_VAR is available to the child process without affecting the parent process's environment.