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GHC.IO.Handle.FD

Portability | non-portable
Stability | internal
Maintainer | libraries@haskell.org

Description
Handle operations implemented by file descriptors (FDs)
Synopsis

stdin :: Handle
stdout :: Handle
stderr :: Handle
openFile :: FilePath -> IOMode -> IO Handle
openBinaryFile :: FilePath -> IOMode -> IO Handle
mkHandleFromFD :: FD -> IODeviceType -> FilePath -> IOMode -> Bool -> Maybe TextEncoding -> IO Handle
fdToHandle :: FD -> IO Handle
fdToHandle' :: CInt -> Maybe IODeviceType -> Bool -> FilePath -> IOMode -> Bool -> IO Handle
isEOF :: IO Bool

Documentation
stdin :: Handle
A handle managing input from the Haskell program's standard input channel.
stdout :: Handle
A handle managing output to the Haskell program's standard output channel.
stderr :: Handle
A handle managing output to the Haskell program's standard error channel.
openFile :: FilePath -> IOMode -> IO Handle

Computation `openFile` `file mode` allocates and returns a new, open handle to manage the file `file`. It manages input if `mode` is `ReadMode`, output if `mode` is `WriteMode` or `AppendMode`, and both input and output if mode is `ReadWriteMode`.

If the file does not exist and it is opened for output, it should be created as a new file. If `mode` is `WriteMode` and the file already exists, then it should be truncated to zero length. Some operating systems delete empty files, so there is no guarantee that the file will exist following an `openFile` with `mode` `WriteMode` unless it is subsequently written to successfully. The handle is positioned at the end of the file if `mode` is `AppendMode`, and otherwise at the beginning (in which case its internal position is 0). The initial buffer mode is implementation-dependent.

This operation may fail with:

- isAlreadyInUseError if the file is already open and cannot be reopened;
- isDoesNotExistError if the file does not exist; or
- isPermissionError if the user does not have permission to open the file.

Note: if you will be working with files containing binary data, you'll want to be using `openBinaryFile`.

openBinaryFile :: FilePath -> IOMode -> IO Handle

Like `openFile`, but open the file in binary mode. On Windows, reading a file in text mode (which is the default) will translate CRLF to LF, and writing will translate LF to CRLF. This is usually what you want with text files. With binary files this is undesirable; also, as usual under Microsoft operating systems, text mode treats control-Z as EOF. Binary mode turns off all special treatment of end-of-line and end-of-file characters. (See also `hSetBinaryMode`.)

mkHandleFromFD :: FD -> IODeviceType -> FilePath -> IOMode -> Bool -> Maybe TextEncoding -> IO Handle
fdToHandle :: FD -> IO Handle
Turn an existing file descriptor into a Handle. This is used by various external libraries to make Handles. Makes a binary Handle. This is for historical reasons; it should probably be a text Handle with the default encoding and newline translation instead.
fdToHandle' :: CInt -> Maybe IODeviceType -> Bool -> FilePath -> IOMode -> Bool -> IO Handle
Old API kept to avoid breaking clients
isEOF :: IO Bool
The computation `isEOF` is identical to `hIsEOF`, except that it works only on `stdin`.
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