Program

class Program

  # The arguments after the program's own name, the way every shell
  # hands them over.
  def self.args : Array(String)

  # The directory the process is in, which is not what `PWD` says.
  # `PWD` is a variable a shell keeps: cmd and PowerShell never set it,
  # so on Windows every program that expanded a relative path panicked
  # ("no base given and PWD is not set"), and on POSIX it is a copy that
  # a program's own `Dir.cd` leaves behind. Nil when the platform has no
  # answer — wasm32-wasi resolves a path against a preopened directory
  # and names none — or when the directory is gone from under the
  # process.
  #
  # 4096 bytes covers POSIX's PATH_MAX and Windows' MAX_PATH; the second
  # try is for a Windows path built with `\\?\`, which reaches 32,767
  # characters and up to three UTF-8 bytes each.
  def self.cwd : String | Nil

  # One variable, or nil. No map of everything: the asking program names
  # what it wants, and a tool that dumps its whole environment into a
  # structure was one `puts` away from leaking it.
  def self.env(name : String) : String | Nil
end