Reading Environment Variables🔗

You can use IO.getEnv to retrieve the value of an environment variable. Since a variable might not be set, it returns an Option String.

def checkUser : IO Unit := do
  let user? ← IO.getEnv "USER"
  match user? with
  | some name => IO.println s!"Hello, {name}!"
  | none      => IO.println "Could not find USER variable."