System.Environment.Compat

Miscellaneous information about the system environment.

Documentation

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 getEnv var returns the value of the environment variable var. For the inverse, POSIX users can use putEnv.

This computation may fail with:

• isDoesNotExistError if the environment variable does not exist.

lookupEnv :: String -> IO (Maybe String)

Return the value of the environment variable var, or Nothing if there is no such value.

For POSIX users, this is equivalent to getEnv.

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.