Filesystem

Simple FilePath‐aware wrappers around standard System.IO computations. These wrappers are designed to work as similarly as possible across various versions of GHC.

In particular, they do not require POSIX file paths to be valid strings, and can therefore open paths regardless of the current locale encoding.

Exports from System.IO

data Handle

Haskell defines operations to read and write characters from and to files, represented by values of type Handle. Each value of this type is a handle: a record used by the Haskell run-time system to manage I/O with file system objects. A handle has at least the following properties:

• whether it manages input or output or both;
• whether it is open, closed or semi-closed;
• whether the object is seekable;
• whether buffering is disabled, or enabled on a line or block basis;
• a buffer (whose length may be zero).

Most handles will also have a current I/O position indicating where the next input or output operation will occur. A handle is readable if it manages only input or both input and output; likewise, it is writable if it manages only output or both input and output. A handle is open when first allocated. Once it is closed it can no longer be used for either input or output, though an implementation cannot re-use its storage while references remain to it. Handles are in the Show and Eq classes. The string produced by showing a handle is system dependent; it should include enough information to identify the handle for debugging. A handle is equal according to == only to itself; no attempt is made to compare the internal state of different handles for equality.

Instances

Eq Handle

Since: base-4.1.0.0

Defined in GHC.IO.Handle.Types

Methods

(==) :: Handle -> Handle -> Bool

(/=) :: Handle -> Handle -> Bool

Show Handle

Since: base-4.1.0.0

Defined in GHC.IO.Handle.Types

Methods

showsPrec :: Int -> Handle -> ShowS

show :: Handle -> String

showList :: [Handle] -> ShowS

data IOMode

See openFile

Constructors

ReadMode

WriteMode

AppendMode

ReadWriteMode

Instances

Enum IOMode

Defined in GHC.IO.IOMode

Methods

succ :: IOMode -> IOMode

pred :: IOMode -> IOMode

toEnum :: Int -> IOMode

fromEnum :: IOMode -> Int

enumFrom :: IOMode -> [IOMode]

enumFromThen :: IOMode -> IOMode -> [IOMode]

enumFromTo :: IOMode -> IOMode -> [IOMode]

enumFromThenTo :: IOMode -> IOMode -> IOMode -> [IOMode]

Eq IOMode

Defined in GHC.IO.IOMode

Methods

(==) :: IOMode -> IOMode -> Bool

(/=) :: IOMode -> IOMode -> Bool

Ord IOMode

Defined in GHC.IO.IOMode

Methods

compare :: IOMode -> IOMode -> Ordering

(<) :: IOMode -> IOMode -> Bool

(<=) :: IOMode -> IOMode -> Bool

(>) :: IOMode -> IOMode -> Bool

(>=) :: IOMode -> IOMode -> Bool

max :: IOMode -> IOMode -> IOMode

min :: IOMode -> IOMode -> IOMode

Read IOMode

Defined in GHC.IO.IOMode

Methods

readsPrec :: Int -> ReadS IOMode

readList :: ReadS [IOMode]

readPrec :: ReadPrec IOMode

readListPrec :: ReadPrec [IOMode]

Show IOMode

Defined in GHC.IO.IOMode

Methods

showsPrec :: Int -> IOMode -> ShowS

show :: IOMode -> String

showList :: [IOMode] -> ShowS

Ix IOMode

Defined in GHC.IO.IOMode

Methods

range :: (IOMode, IOMode) -> [IOMode]

index :: (IOMode, IOMode) -> IOMode -> Int

unsafeIndex :: (IOMode, IOMode) -> IOMode -> Int

inRange :: (IOMode, IOMode) -> IOMode -> Bool

rangeSize :: (IOMode, IOMode) -> Int

unsafeRangeSize :: (IOMode, IOMode) -> Int

Files

isFile :: FilePath -> IO Bool

Check if a file exists at the given path.

Any non‐directory object, including devices and pipes, are considered to be files. Symbolic links are resolved to their targets before checking their type.

This computation does not throw exceptions.

getModified :: FilePath -> IO UTCTime

Get when the object at a given path was last modified.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

Since: 0.2

getSize :: FilePath -> IO Integer

Get the size of an object at a given path. For special objects like links or directories, the size is filesystem‐ and platform‐dependent.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

Since: 0.2

copyFile

Arguments

:: FilePath

Old location

-> FilePath

New location

-> IO ()

Copy the content and permissions of a file to a new entry in the filesystem. If a file already exists at the new location, it will be replaced. Copying a file is not atomic.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

Since: 0.1.1

copyFileContent

Arguments

:: FilePath

Old location

-> FilePath

New location

-> IO ()

Copy the content of a file to a new entry in the filesystem. If a file already exists at the new location, it will be replaced. Copying a file is not atomic.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

Since: 0.2.4 / 0.3.4

copyPermissions

Arguments

:: FilePath

Old location

-> FilePath

New location

-> IO ()

Copy the permissions from one path to another. Both paths must already exist.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

Since: 0.2.4 / 0.3.4

removeFile :: FilePath -> IO ()

Remove a file. This will fail if the file does not exist.

This computation cannot remove directories. For that, use removeDirectory or removeTree.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

Binary files

openFile :: FilePath -> IOMode -> IO Handle

Open a file in binary mode, and return an open Handle. The Handle should be closed with hClose when it is no longer needed.

withFile is easier to use, because it will handle the Handle’s lifetime automatically.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

withFile :: FilePath -> IOMode -> (Handle -> IO a) -> IO a

Open a file in binary mode, and pass its Handle to a provided computation. The Handle will be automatically closed when the computation returns.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

readFile :: FilePath -> IO ByteString

Read in the entire content of a binary file.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

writeFile :: FilePath -> ByteString -> IO ()

Replace the entire content of a binary file with the provided ByteString.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

appendFile :: FilePath -> ByteString -> IO ()

Append a ByteString to a file. If the file does not exist, it will be created.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

Text files

openTextFile :: FilePath -> IOMode -> IO Handle

Open a file in text mode, and return an open Handle. The Handle should be closed with hClose when it is no longer needed.

withTextFile is easier to use, because it will handle the Handle’s lifetime automatically.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

withTextFile :: FilePath -> IOMode -> (Handle -> IO a) -> IO a

Open a file in text mode, and pass its Handle to a provided computation. The Handle will be automatically closed when the computation returns.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

readTextFile :: FilePath -> IO Text

Read in the entire content of a text file.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

writeTextFile :: FilePath -> Text -> IO ()

Replace the entire content of a text file with the provided Text.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

appendTextFile :: FilePath -> Text -> IO ()

Append Text to a file. If the file does not exist, it will be created.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

Directories

isDirectory :: FilePath -> IO Bool

Check if a directory exists at the given path.

Symbolic links are resolved to their targets before checking their type.

This computation does not throw exceptions.

canonicalizePath :: FilePath -> IO FilePath

Resolve symlinks and ".." path elements to return a canonical path. It is intended that two paths referring to the same object will always resolve to the same canonical path.

Note that on many operating systems, it is impossible to guarantee that two paths to the same file will resolve to the same canonical path.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

Since: 0.1.1

listDirectory :: FilePath -> IO [FilePath]

List objects in a directory, excluding "." and "..". Each returned FilePath includes the path of the directory. Entries are not sorted.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

Creating directories

createDirectory

Arguments

:: Bool

Succeed if the directory already exists

-> FilePath

-> IO ()

Create a directory at a given path. The user may choose whether it is an error for a directory to already exist at that path.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

createTree :: FilePath -> IO ()

Create a directory at a given path, including any parents which might be missing.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

Removing directories

removeDirectory :: FilePath -> IO ()

Remove an empty directory.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

removeTree :: FilePath -> IO ()

Recursively remove a directory tree rooted at the given path.

This computation does not follow symlinks. If the tree contains symlinks, the links themselves will be removed, but not the objects they point to.

If the root path is a symlink, then it will be treated as if it were a regular directory.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

Current working directory

getWorkingDirectory :: IO FilePath

Get the current working directory.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

setWorkingDirectory :: FilePath -> IO ()

Set the current working directory.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

Commonly used paths

getHomeDirectory :: IO FilePath

Get the user’s home directory. This is useful for building paths to more specific directories.

For directing the user to open or safe a document, use getDocumentsDirectory.

For data files the user does not explicitly create, such as automatic saves, use getAppDataDirectory.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

getDesktopDirectory :: IO FilePath

Get the user’s desktop directory. This is a good starting point for file dialogs and other user queries. For data files the user does not explicitly create, such as automatic saves, use getAppDataDirectory.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

getDocumentsDirectory :: IO FilePath

Get the user’s documents directory. This is a good place to save user‐created files. For data files the user does not explicitly create, such as automatic saves, use getAppDataDirectory.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

getAppDataDirectory :: Text -> IO FilePath

Get the user’s application data directory, given an application label. This directory is where applications should store data the user did not explicitly create, such as databases and automatic saves.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

getAppCacheDirectory :: Text -> IO FilePath

Get the user’s application cache directory, given an application label. This directory is where applications should store caches, which might be large and can be safely deleted.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

getAppConfigDirectory :: Text -> IO FilePath

Get the user’s application configuration directory, given an application label. This directory is where applications should store their configurations and settings.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.

Other

rename :: FilePath -> FilePath -> IO ()

Rename a filesystem object.

This computation throws IOError on failure. See “Classifying I/O errors” in the System.IO.Error documentation for information on why the failure occured.