| Copyright | (c) The University of Glasgow 2001 |
|---|---|
| License | BSD-style (see the file libraries/base/LICENSE) |
| Maintainer | libraries@haskell.org |
| Stability | provisional |
| Portability | portable |
| Safe Haskell | Safe |
| Language | Haskell2010 |
System.Environment
Description
Miscellaneous information about the system environment.
Synopsis
- getArgs :: IO [String]
- getProgName :: IO String
- executablePath :: Maybe (IO (Maybe FilePath))
- 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
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.
executablePath :: Maybe (IO (Maybe FilePath)) Source #
Get an action to query the absolute pathname of the current executable.
If the operating system provides a reliable way to determine the current
executable, return the query action, otherwise return Nothing. The action
is defined on FreeBSD, Linux, MacOS, NetBSD, and Windows.
Even where the query action is defined, there may be situations where no
result is available, e.g. if the executable file was deleted while the
program is running. Therefore the result of the query action is a Maybe
FilePath.
Note that for scripts and interactive sessions, the result is the path to the interpreter (e.g. ghci.)
Since: base-4.17.0.0
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
getEnv :: String -> IO String Source #
Computation getEnv var returns the value
of the environment variable var. For the inverse, the
setEnv function can be used.
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.
Since: base-4.6.0.0
setEnv :: String -> String -> IO () Source #
setEnv name value sets the specified environment variable to value.
Early versions of this function operated under the mistaken belief that setting an environment variable to the empty string on Windows removes that environment variable from the environment. For the sake of compatibility, it adopted that behavior on POSIX. In particular
setEnv name ""
has the same effect as
unsetEnv name
If you'd like to be able to set environment variables to blank strings,
use setEnv.
Throws IOException if name is the empty string or
contains an equals sign.
Since: base-4.7.0.0
unsetEnv :: String -> IO () Source #
unsetEnv 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.
Since: base-4.7.0.0
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.