/Haskell 8


Copyright (c) Habib Alamin 2017
License BSD-style (see the file libraries/base/LICENSE)
Maintainer [email protected]
Stability provisional
Portability portable
Safe Haskell Safe
Language Haskell2010


A setEnv implementation that allows blank environment variables. Mimics the Env module from the unix package, but with support for Windows too.

The matrix of platforms that:

  • support putenv(FOO) to unset environment variables,
  • support putenv("FOO=") to unset environment variables or set them to blank values,
  • support unsetenv to unset environment variables,
  • support setenv to set environment variables,
  • etc.

is very complicated. Some platforms don't support unsetting of environment variables at all.

getExecutablePath :: IO FilePath Source

Returns the absolute pathname of the current executable.

Note that for scripts and interactive sessions, this is the path to the interpreter (e.g. ghci.)

Since base, getExecutablePath resolves symlinks on Windows. If an executable is launched through a symlink, getExecutablePath returns the absolute path of the original executable.

Since: base-

getArgs :: IO [String] Source

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

getProgName :: IO String Source

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.

withArgs :: [String] -> IO a -> IO a Source

withArgs args act - while executing action act, have getArgs return args.

withProgName :: String -> IO a -> IO a Source

withProgName name act - while executing action act, have getProgName return name.

getEnvironment :: IO [(String, String)] Source

getEnvironment retrieves the entire environment as a list of (key,value) pairs.

If an environment entry does not contain an '=' character, the key is the whole entry and the value is the empty string.

getEnv :: String -> IO (Maybe String) Source

Similar to lookupEnv.

getEnvDefault Source


:: String

variable name

-> String

fallback value

-> IO String

variable value or fallback value

Get an environment value or a default value.

setEnv Source


:: String

variable name

-> String

variable value

-> Bool


-> IO ()

Like setEnv, but allows blank environment values and mimics the function signature of setEnv from the unix package.

unsetEnv :: String -> IO () Source

Like unsetEnv, but allows for the removal of blank environment variables. May throw an exception if the underlying platform doesn't support unsetting of environment variables.

© The University of Glasgow and others
Licensed under a BSD-style license (see top of the page).