base-4.0.0.0: Basic librariesContentsIndex
System.Environment
Portabilityportable
Stabilityprovisional
Maintainerlibraries@haskell.org
Description
Miscellaneous information about the system environment.
Synopsis
getArgs :: IO [String]
getProgName :: IO String
getEnv :: String -> IO String
withArgs :: [String] -> IO a -> IO a
withProgName :: String -> IO a -> IO a
getEnvironment :: IO [(String, String)]
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.

This computation may fail with:

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

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