Copyright	(c) Habib Alamin 2017
License	BSD-style (see the file libraries/base/LICENSE)
Maintainer	libraries@haskell.org
Stability	provisional
Portability	portable
Safe Haskell	Trustworthy
Language	Haskell2010

GHC.Internal.System.Environment.Blank

Description

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.

Synopsis

getArgs :: IO [String]
getProgName :: IO String
getExecutablePath :: IO FilePath
withArgs :: [String] -> IO a -> IO a
withProgName :: String -> IO a -> IO a
getEnvironment :: IO [(String, String)]
getEnv :: String -> IO (Maybe String)
getEnvDefault :: String -> String -> IO String
setEnv :: String -> String -> Bool -> IO ()
unsetEnv :: String -> IO ()

Documentation

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.

getExecutablePath :: IO FilePath Source #

Returns the absolute pathname of the current executable, or argv[0] if the operating system does not provide a reliable way query 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.

If the executable has been deleted, behaviour is ill-defined and varies by operating system. See executablePath for a more reliable way to query the current executable.

@since base-4.6.0.0

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 #

Arguments

:: String	variable name
-> String	fallback value
-> IO String	variable value or fallback value

Get an environment value or a default value.

setEnv Source #

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.

Beware that this function must not be executed concurrently with getEnv, lookupEnv, getEnvironment and such. One thread reading environment variables at the same time with another one modifying them can result in a segfault, see Setenv is not Thread Safe for discussion.

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.

Beware that this function must not be executed concurrently with getEnv, lookupEnv, getEnvironment and such. One thread reading environment variables at the same time with another one modifying them can result in a segfault, see Setenv is not Thread Safe for discussion.