Portability	non-portable (requires POSIX)
Stability	provisional
Maintainer	libraries@haskell.org

System.Posix.IO

Contents

Input / Output

Description

POSIX IO support. These types and functions correspond to the unix functions open(2), close(2), etc. For more portable functions which are more like fopen(3) and friends from stdio.h, see System.IO.

Synopsis

Input / Output

Standard file descriptors

stdInput, stdError, stdOutput :: Fd Source

Opening and closing files

data OpenMode Source

Constructors

ReadOnly
WriteOnly
ReadWrite

data OpenFileFlags Source

Correspond to some of the int flags from C's fcntl.h.

Constructors

OpenFileFlags
Fields append :: Bool O_APPEND exclusive :: Bool O_EXCL noctty :: Bool O_NOCTTY nonBlock :: Bool O_NONBLOCK trunc :: Bool O_TRUNC

defaultFileFlags :: OpenFileFlags Source

Default values for the OpenFileFlags type. False for each of append, exclusive, noctty, nonBlock, and trunc.

openFd Source

Arguments

:: FilePath
-> OpenMode
-> Maybe FileMode	Just x => creates the file with the given modes, Nothing => the file must exist.
-> OpenFileFlags
-> IO Fd

Open and optionally create this file. See System.Posix.Files for information on how to use the FileMode type.

createFile :: FilePath -> FileMode -> IO Fd Source

Create and open this file in WriteOnly mode. A special case of openFd. See System.Posix.Files for information on how to use the FileMode type.

closeFd :: Fd -> IO ()Source

Close this file descriptor. May throw an exception if this is an invalid descriptor.

Reading/writing data

Programmers using the fdRead and fdWrite API should be aware that EAGAIN exceptions may occur for non-blocking IO!

fdRead Source

Arguments

:: Fd
-> ByteCount	How many bytes to read
-> IO (String, ByteCount)	The bytes read, how many bytes were read.

Read data from an Fd and convert it to a String using the locale encoding. Throws an exception if this is an invalid descriptor, or EOF has been reached.

fdWrite :: Fd -> String -> IO ByteCount Source

Write a String to an Fd using the locale encoding.

fdReadBuf Source

Arguments

:: Fd
-> Ptr Word8	Memory in which to put the data
-> ByteCount	Maximum number of bytes to read
-> IO ByteCount	Number of bytes read (zero for EOF)

Read data from an Fd into memory. This is exactly equivalent to the POSIX read function.

fdWriteBuf Source

Arguments

:: Fd
-> Ptr Word8	Memory containing the data to write
-> ByteCount	Maximum number of bytes to write
-> IO ByteCount	Number of bytes written

Write data from memory to an Fd. This is exactly equivalent to the POSIX write function.

Seeking

fdSeek :: Fd -> SeekMode -> FileOffset -> IO FileOffset Source

May throw an exception if this is an invalid descriptor.

File options

data FdOption Source

Constructors

AppendOnWrite	O_APPEND
CloseOnExec	FD_CLOEXEC
NonBlockingRead	O_NONBLOCK
SynchronousWrites	O_SYNC

queryFdOption :: Fd -> FdOption -> IO Bool Source

May throw an exception if this is an invalid descriptor.

setFdOption :: Fd -> FdOption -> Bool -> IO ()Source

May throw an exception if this is an invalid descriptor.

Locking

type FileLock = (LockRequest, SeekMode, FileOffset, FileOffset)Source

data LockRequest Source

Constructors

ReadLock
WriteLock
Unlock

getLock :: Fd -> FileLock -> IO (Maybe (ProcessID, FileLock))Source

May throw an exception if this is an invalid descriptor.

setLock :: Fd -> FileLock -> IO ()Source

May throw an exception if this is an invalid descriptor.

waitToSetLock :: Fd -> FileLock -> IO ()Source

May throw an exception if this is an invalid descriptor.

Pipes

createPipe :: IO (Fd, Fd)Source

The createPipe function creates a pair of connected file descriptors. The first component is the fd to read from, the second is the write end. Although pipes may be bidirectional, this behaviour is not portable and programmers should use two separate pipes for this purpose. May throw an exception if this is an invalid descriptor.

Duplicating file descriptors

dup :: Fd -> IO Fd Source

May throw an exception if this is an invalid descriptor.

dupTo :: Fd -> Fd -> IO Fd Source

May throw an exception if this is an invalid descriptor.

Converting file descriptors to/from Handles

handleToFd :: Handle -> IO Fd Source

Extracts the Fd from a Handle. This function has the side effect of closing the Handle and flushing its write buffer, if necessary.

fdToHandle :: Fd -> IO Handle Source

Converts an Fd into a Handle that can be used with the standard Haskell IO library (see System.IO).

GHC only: this function has the side effect of putting the Fd into non-blocking mode (O_NONBLOCK) due to the way the standard IO library implements multithreaded I/O.