| Copyright | (c) The University of Glasgow 2001 |
|---|---|
| License | (c) The University of Glasgow 2001 |
| Maintainer | libraries@haskell.org |
| Stability | provisional |
| Portability | portable |
| Safe Haskell | Safe |
System.Environment
Description
Miscellaneous information about the system environment.
- getArgs :: IO [String]
- getProgName :: IO String
- getExecutablePath :: IO FilePath
- getEnv :: String -> IO String
- lookupEnv :: String -> IO (Maybe String)
- setEnv :: String -> String -> IO ()
- unsetEnv :: String -> IO ()
- withArgs :: [String] -> IO a -> IO a
- withProgName :: String -> IO a -> IO a
- getEnvironment :: IO [(String, String)]
Documentation
Computation getArgs returns a list of the program's command
line arguments (not including the program name).
getProgName :: IO StringSource
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 FilePathSource
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.)
getEnv :: String -> IO StringSource
Computation getEnv var returns the value
of the environment variable var. For the inverse, POSIX users
can use putEnv.
This computation may fail with:
-
isDoesNotExistErrorif the environment variable does not exist.
lookupEnv :: String -> IO (Maybe String)Source
Return the value of the environment variable var, or Nothing if
there is no such value.
For POSIX users, this is equivalent to getEnv.
setEnv :: String -> String -> IO ()Source
setEnv name value sets the specified environment variable to value.
On Windows setting an environment variable to the empty string removes that environment variable from the environment. For the sake of compatibility we adopt that behavior. In particular
setEnv name ""
has the same effect as
unsetEnv name
If you don't care about Windows support and want to set an environment
variable to the empty string use System.Posix.Env.setEnv from the unix
package instead.
Throws IOException if name is the empty string or
contains an equals sign.
unsetEnv :: String -> IO ()Source
unSet name removes the specified environment variable from the
environment of the current process.
Throws IOException if name is the empty string or
contains an equals sign.
withProgName :: String -> IO a -> IO aSource
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.