| 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 |
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. I think AIX is screwed, but we don't support it. The whole situation with setenv(3), unsetenv(3), and putenv(3) is not good. Even mingw32 adds its own crap to the pile, but luckily, we can just use Windows' native environment functions to sidestep the issue.
#12494
Synopsis
- getExecutablePath :: IO FilePath
- getArgs :: IO [String]
- getProgName :: IO String
- 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
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 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: base-4.6.0.0
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.
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.
Arguments
| :: String | variable name |
| -> String | fallback value |
| -> IO String | variable value or fallback value |
Get an environment value or a default value.