System.Environment.Blank

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.

Documentation

getExecutablePath :: IO FilePath

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

Since: 4.6.0.0

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.

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

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

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

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

getEnvironment :: IO [(String, String)]

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)

Similar to lookupEnv.

getEnvDefault

Arguments

:: String

variable name

-> String

fallback value

-> IO String

variable value or fallback value

Get an environment value or a default value.

setEnv

Arguments

:: String

variable name

-> String

variable value

-> Bool

overwrite

-> IO ()

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

unsetEnv :: String -> IO ()

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.