39 System.Environment
Date: 2010-07-20 13:11:00

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## Chapter 39
System.Environment

module System.Environment (
getArgs, getProgName, getEnv
) where

getArgs :: IO [String]

  Computation getArgs returns a list of the program’s command line arguments (not including the program name).

getProgName :: IO String

  Computation getProgName returns the name of the program as it was invoked.

  However, this is hard-to-impossible to implement on some non-Unix OSes, so instead, for maximum portability, we just return the leafname of the program as invoked. Even then there are some differences between platforms: on Windows, for example, a program invoked as foo is probably really FOO.EXE, and that is what getProgName will return.

getEnv :: String -> IO String

  Computation getEnvvar returns the value of the environment variable var.

  This computation may fail with:

  - System.IO.Error.isDoesNotExistError if the environment variable does not exist.

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