base-4.7.0.2: Basic libraries

Copyright | (c) The University of Glasgow, 1994-2008
License | see libraries/base/LICENSE
Maintainer | libraries@haskell.org
Stability | internal
Portability | non-portable
Safe Haskell | Trustworthy
Language | Haskell2010

GHC.IO.Handle.FD

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
- openFileBlocking :: 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`.)

openFileBlocking :: FilePath -> IOMode -> IO Handle

Like `openFile`, but opens the file in ordinary blocking mode. This can be useful for opening a FIFO for reading: if we open in non-blocking mode then the open will fail if there are no writers, whereas a blocking open will block until a writer appears.

Since: 4.4.0.0

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`.