Copyright	(c) Neil Mitchell 2005-2014
License	BSD3
Maintainer	ndmitchell@gmail.com
Stability	stable
Portability	portable
Safe Haskell	Safe
Language	Haskell98

System.FilePath.Posix

Contents

Separator predicates
$PATH methods
Extension functions
Filename/directory functions
Drive functions
Trailing slash functions
File name manipulations

Description

A library for FilePath manipulations, using Posix style paths on all platforms. Importing System.FilePath is usually better.

Given the eample FilePath: /directory/file.ext

We can use the following functions to extract pieces.

takeFileName gives "file.ext"
takeDirectory gives "/directory"
takeExtension gives ".ext"
dropExtension gives "/directory/file"
takeBaseName gives "file"

And we could have built an equivalent path with the following expressions:

"/directory" </> "file.ext".
"/directory/file" <.> "ext".
"/directory/file.txt" -<.> "ext".

Each function in this module is documented with several examples, which are also used as tests.

Here are a few examples of using the filepath functions together:

Example 1: Find the possible locations of a Haskell module Test imported from module Main:

[replaceFileName path_to_main "Test" <.> ext | ext <- ["hs","lhs"] ]

Example 2: Download a file from url and save it to disk:

do let file = makeValid url
   System.IO.createDirectoryIfMissing True (takeDirectory file)

Example 3: Compile a Haskell file, putting the .hi file under interface:

takeDirectory file </> "interface" </> (takeFileName file -<.> "hi")

References: [1] Naming Files, Paths and Namespaces (Microsoft MSDN)

Synopsis

Separator predicates

type FilePath = String Source

File and directory names are values of type String, whose precise meaning is operating system dependent. Files can be opened, yielding a handle which can then be used to operate on the contents of that file.

pathSeparator :: Char Source

The character that separates directories. In the case where more than one character is possible, pathSeparator is the 'ideal' one.

Windows: pathSeparator == '\\'
Posix:   pathSeparator ==  '/'
isPathSeparator pathSeparator

pathSeparators :: [Char] Source

The list of all possible separators.

Windows: pathSeparators == ['\\', '/']
Posix:   pathSeparators == ['/']
pathSeparator `elem` pathSeparators

isPathSeparator :: Char -> Bool Source

Rather than using (== pathSeparator), use this. Test if something is a path separator.

isPathSeparator a == (a `elem` pathSeparators)

searchPathSeparator :: Char Source

The character that is used to separate the entries in the $PATH environment variable.

Windows: searchPathSeparator == ';'
Posix:   searchPathSeparator == ':'

isSearchPathSeparator :: Char -> Bool Source

Is the character a file separator?

isSearchPathSeparator a == (a == searchPathSeparator)

extSeparator :: Char Source

File extension character

extSeparator == '.'

isExtSeparator :: Char -> Bool Source

Is the character an extension character?

isExtSeparator a == (a == extSeparator)

`$PATH` methods

splitSearchPath :: String -> [FilePath] Source

Take a string, split it on the searchPathSeparator character.

Follows the recommendations in http://www.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap08.html

Posix:   splitSearchPath "File1:File2:File3"  == ["File1","File2","File3"]
Posix:   splitSearchPath "File1::File2:File3" == ["File1",".","File2","File3"]
Windows: splitSearchPath "File1;File2;File3"  == ["File1","File2","File3"]
Windows: splitSearchPath "File1;;File2;File3" == ["File1","File2","File3"]
Windows: splitSearchPath "File1;\"File2\";File3" == ["File1","File2","File3"]

getSearchPath :: IO [FilePath] Source

Get a list of FilePaths in the $PATH variable.

Extension functions

splitExtension :: FilePath -> (String, String) Source

Split on the extension. addExtension is the inverse.

splitExtension "/directory/path.ext" == ("/directory/path",".ext")
uncurry (++) (splitExtension x) == x
Valid x => uncurry addExtension (splitExtension x) == x
splitExtension "file.txt" == ("file",".txt")
splitExtension "file" == ("file","")
splitExtension "file/file.txt" == ("file/file",".txt")
splitExtension "file.txt/boris" == ("file.txt/boris","")
splitExtension "file.txt/boris.ext" == ("file.txt/boris",".ext")
splitExtension "file/path.txt.bob.fred" == ("file/path.txt.bob",".fred")
splitExtension "file/path.txt/" == ("file/path.txt/","")

takeExtension :: FilePath -> String Source

Get the extension of a file, returns "" for no extension, .ext otherwise.

takeExtension "/directory/path.ext" == ".ext"
takeExtension x == snd (splitExtension x)
Valid x => takeExtension (addExtension x "ext") == ".ext"
Valid x => takeExtension (replaceExtension x "ext") == ".ext"

replaceExtension :: FilePath -> String -> FilePath Source

Set the extension of a file, overwriting one if already present, equivalent to <.>.

replaceExtension "/directory/path.txt" "ext" == "/directory/path.ext"
replaceExtension "/directory/path.txt" ".ext" == "/directory/path.ext"
replaceExtension "file.txt" ".bob" == "file.bob"
replaceExtension "file.txt" "bob" == "file.bob"
replaceExtension "file" ".bob" == "file.bob"
replaceExtension "file.txt" "" == "file"
replaceExtension "file.fred.bob" "txt" == "file.fred.txt"
replaceExtension x y == addExtension (dropExtension x) y

(-<.>) :: FilePath -> String -> FilePath infixr 7 Source

Remove the current extension and add another, equivalent to replaceExtension.

"/directory/path.txt" -<.> "ext" == "/directory/path.ext"
"/directory/path.txt" -<.> ".ext" == "/directory/path.ext"
"foo.o" -<.> "c" == "foo.c"

dropExtension :: FilePath -> FilePath Source

Remove last extension, and the "." preceding it.

dropExtension "/directory/path.ext" == "/directory/path"
dropExtension x == fst (splitExtension x)

addExtension :: FilePath -> String -> FilePath Source

Add an extension, even if there is already one there, equivalent to <.>.

addExtension "/directory/path" "ext" == "/directory/path.ext"
addExtension "file.txt" "bib" == "file.txt.bib"
addExtension "file." ".bib" == "file..bib"
addExtension "file" ".bib" == "file.bib"
addExtension "/" "x" == "/.x"
Valid x => takeFileName (addExtension (addTrailingPathSeparator x) "ext") == ".ext"
Windows: addExtension "\\\\share" ".txt" == "\\\\share\\.txt"

hasExtension :: FilePath -> Bool Source

Does the given filename have an extension?

hasExtension "/directory/path.ext" == True
hasExtension "/directory/path" == False
null (takeExtension x) == not (hasExtension x)

(<.>) :: FilePath -> String -> FilePath infixr 7 Source

Add an extension, even if there is already one there, equivalent to addExtension.

"/directory/path" <.> "ext" == "/directory/path.ext"
"/directory/path" <.> ".ext" == "/directory/path.ext"

splitExtensions :: FilePath -> (FilePath, String) Source

Split on all extensions.

splitExtensions "/directory/path.ext" == ("/directory/path",".ext")
splitExtensions "file.tar.gz" == ("file",".tar.gz")
uncurry (++) (splitExtensions x) == x
Valid x => uncurry addExtension (splitExtensions x) == x
splitExtensions "file.tar.gz" == ("file",".tar.gz")

dropExtensions :: FilePath -> FilePath Source

Drop all extensions.

dropExtensions "/directory/path.ext" == "/directory/path"
dropExtensions "file.tar.gz" == "file"
not $ hasExtension $ dropExtensions x
not $ any isExtSeparator $ takeFileName $ dropExtensions x

takeExtensions :: FilePath -> String Source

Get all extensions.

takeExtensions "/directory/path.ext" == ".ext"
takeExtensions "file.tar.gz" == ".tar.gz"

Filename/directory functions

splitFileName :: FilePath -> (String, String) Source

Split a filename into directory and file. combine is the inverse. The first component will often end with a trailing slash.

splitFileName "/directory/file.ext" == ("/directory/","file.ext")
Valid x => uncurry (</>) (splitFileName x) == x || fst (splitFileName x) == "./"
Valid x => isValid (fst (splitFileName x))
splitFileName "file/bob.txt" == ("file/", "bob.txt")
splitFileName "file/" == ("file/", "")
splitFileName "bob" == ("./", "bob")
Posix:   splitFileName "/" == ("/","")
Windows: splitFileName "c:" == ("c:","")

takeFileName :: FilePath -> FilePath Source

Get the file name.

takeFileName "/directory/file.ext" == "file.ext"
takeFileName "test/" == ""
takeFileName x `isSuffixOf` x
takeFileName x == snd (splitFileName x)
Valid x => takeFileName (replaceFileName x "fred") == "fred"
Valid x => takeFileName (x </> "fred") == "fred"
Valid x => isRelative (takeFileName x)

replaceFileName :: FilePath -> String -> FilePath Source

Set the filename.

replaceFileName "/directory/other.txt" "file.ext" == "/directory/file.ext"
Valid x => replaceFileName x (takeFileName x) == x

dropFileName :: FilePath -> FilePath Source

Drop the filename. Unlike takeDirectory, this function will leave a trailing path separator on the directory.

dropFileName "/directory/file.ext" == "/directory/"
dropFileName x == fst (splitFileName x)

takeBaseName :: FilePath -> String Source

Get the base name, without an extension or path.

takeBaseName "/directory/file.ext" == "file"
takeBaseName "file/test.txt" == "test"
takeBaseName "dave.ext" == "dave"
takeBaseName "" == ""
takeBaseName "test" == "test"
takeBaseName (addTrailingPathSeparator x) == ""
takeBaseName "file/file.tar.gz" == "file.tar"

replaceBaseName :: FilePath -> String -> FilePath Source

Set the base name.

replaceBaseName "/directory/other.ext" "file" == "/directory/file.ext"
replaceBaseName "file/test.txt" "bob" == "file/bob.txt"
replaceBaseName "fred" "bill" == "bill"
replaceBaseName "/dave/fred/bob.gz.tar" "new" == "/dave/fred/new.tar"
Valid x => replaceBaseName x (takeBaseName x) == x

takeDirectory :: FilePath -> FilePath Source

Get the directory name, move up one level.

          takeDirectory "/directory/other.ext" == "/directory"
          takeDirectory x `isPrefixOf` x || takeDirectory x == "."
          takeDirectory "foo" == "."
          takeDirectory "/" == "/"
          takeDirectory "/foo" == "/"
          takeDirectory "/foo/bar/baz" == "/foo/bar"
          takeDirectory "/foo/bar/baz/" == "/foo/bar/baz"
          takeDirectory "foo/bar/baz" == "foo/bar"
Windows:  takeDirectory "foo\\bar" == "foo"
Windows:  takeDirectory "foo\\bar\\\\" == "foo\\bar"
Windows:  takeDirectory "C:\\" == "C:\\"

replaceDirectory :: FilePath -> String -> FilePath Source

Set the directory, keeping the filename the same.

replaceDirectory "root/file.ext" "/directory/" == "/directory/file.ext"
Valid x => replaceDirectory x (takeDirectory x) `equalFilePath` x

combine :: FilePath -> FilePath -> FilePath Source

Combine two paths, if the second path starts with a path separator or a drive letter, then it returns the second.

Valid x => combine (takeDirectory x) (takeFileName x) `equalFilePath` x

Combined: > Posix: combine "" "test" == "test" > Posix: combine "home" "bob" == "home/bob" > Posix: combine "x:" "foo" == "x:/foo" > Windows: combine C:\\foo "bar" == C:\\foo\\bar > Windows: combine "home" "bob" == "home\bob"

Not combined: > Posix: combine "home" "bob" == "bob" > Windows: combine "home" C:\\bob == C:\\bob

Not combined (tricky): On Windows, if a filepath starts with a single slash, it is relative to the root of the current drive. In [1], this is (confusingly) referred to as an absolute path. The current behavior of combine is to never combine these forms.

Windows: combine "home" "/bob" == "/bob"
Windows: combine "home" "\\bob" == "\\bob"
Windows: combine "C:\\home" "\\bob" == "\\bob"

On Windows, from [1]: "If a file name begins with only a disk designator but not the backslash after the colon, it is interpreted as a relative path to the current directory on the drive with the specified letter." The current behavior of combine is to never combine these forms.

Windows: combine "D:\\foo" "C:bar" == "C:bar"
Windows: combine "C:\\foo" "C:bar" == "C:bar"

(</>) :: FilePath -> FilePath -> FilePath infixr 5 Source

Join two values with a path separator. For examples and caveats see the equivalent function combine.

Posix:   "/directory" </> "file.ext" == "/directory/file.ext"
Windows: "/directory" </> "file.ext" == "/directory\\file.ext"

splitPath :: FilePath -> [FilePath] Source

Split a path by the directory separator.

splitPath "/directory/file.ext" == ["/","directory/","file.ext"]
concat (splitPath x) == x
splitPath "test//item/" == ["test//","item/"]
splitPath "test/item/file" == ["test/","item/","file"]
splitPath "" == []
Windows: splitPath "c:\\test\\path" == ["c:\\","test\\","path"]
Posix:   splitPath "/file/test" == ["/","file/","test"]

joinPath :: [FilePath] -> FilePath Source

Join path elements back together.

joinPath ["/","directory/","file.ext"] == "/directory/file.ext"
Valid x => joinPath (splitPath x) == x
joinPath [] == ""
Posix: joinPath ["test","file","path"] == "test/file/path"

splitDirectories :: FilePath -> [FilePath] Source

Just as splitPath, but don't add the trailing slashes to each element.

         splitDirectories "/directory/file.ext" == ["/","directory","file.ext"]
         splitDirectories "test/file" == ["test","file"]
         splitDirectories "/test/file" == ["/","test","file"]
Windows: splitDirectories "C:\\test\\file" == ["C:\\", "test", "file"]
         Valid x => joinPath (splitDirectories x) `equalFilePath` x
         splitDirectories "" == []
Windows: splitDirectories "C:\\test\\\\\\file" == ["C:\\", "test", "file"]
         splitDirectories "/test///file" == ["/","test","file"]

Drive functions

splitDrive :: FilePath -> (FilePath, FilePath) Source

Split a path into a drive and a path. On Posix, / is a Drive.

uncurry (++) (splitDrive x) == x
Windows: splitDrive "file" == ("","file")
Windows: splitDrive "c:/file" == ("c:/","file")
Windows: splitDrive "c:\\file" == ("c:\\","file")
Windows: splitDrive "\\\\shared\\test" == ("\\\\shared\\","test")
Windows: splitDrive "\\\\shared" == ("\\\\shared","")
Windows: splitDrive "\\\\?\\UNC\\shared\\file" == ("\\\\?\\UNC\\shared\\","file")
Windows: splitDrive "\\\\?\\UNCshared\\file" == ("\\\\?\\","UNCshared\\file")
Windows: splitDrive "\\\\?\\d:\\file" == ("\\\\?\\d:\\","file")
Windows: splitDrive "/d" == ("","/d")
Posix:   splitDrive "/test" == ("/","test")
Posix:   splitDrive "//test" == ("//","test")
Posix:   splitDrive "test/file" == ("","test/file")
Posix:   splitDrive "file" == ("","file")

joinDrive :: FilePath -> FilePath -> FilePath Source

Join a drive and the rest of the path.

Valid x => uncurry joinDrive (splitDrive x) == x
Windows: joinDrive "C:" "foo" == "C:foo"
Windows: joinDrive "C:\\" "bar" == "C:\\bar"
Windows: joinDrive "\\\\share" "foo" == "\\\\share\\foo"
Windows: joinDrive "/:" "foo" == "/:\\foo"

takeDrive :: FilePath -> FilePath Source

Get the drive from a filepath.

takeDrive x == fst (splitDrive x)

hasDrive :: FilePath -> Bool Source

Does a path have a drive.

not (hasDrive x) == null (takeDrive x)
Posix:   hasDrive "/foo" == True
Windows: hasDrive "C:\\foo" == True
Windows: hasDrive "C:foo" == True
         hasDrive "foo" == False
         hasDrive "" == False

dropDrive :: FilePath -> FilePath Source

Delete the drive, if it exists.

dropDrive x == snd (splitDrive x)

isDrive :: FilePath -> Bool Source

Is an element a drive

Posix:   isDrive "/" == True
Posix:   isDrive "/foo" == False
Windows: isDrive "C:\\" == True
Windows: isDrive "C:\\foo" == False
         isDrive "" == False

Trailing slash functions

hasTrailingPathSeparator :: FilePath -> Bool Source

Is an item either a directory or the last character a path separator?

hasTrailingPathSeparator "test" == False
hasTrailingPathSeparator "test/" == True

addTrailingPathSeparator :: FilePath -> FilePath Source

Add a trailing file path separator if one is not already present.

hasTrailingPathSeparator (addTrailingPathSeparator x)
hasTrailingPathSeparator x ==> addTrailingPathSeparator x == x
Posix:    addTrailingPathSeparator "test/rest" == "test/rest/"

dropTrailingPathSeparator :: FilePath -> FilePath Source

Remove any trailing path separators

dropTrailingPathSeparator "file/test/" == "file/test"
          dropTrailingPathSeparator "/" == "/"
Windows:  dropTrailingPathSeparator "\\" == "\\"
Posix:    not (hasTrailingPathSeparator (dropTrailingPathSeparator x)) || isDrive x

File name manipulations

normalise :: FilePath -> FilePath Source

Normalise a file

// outside of the drive can be made blank
/ -> pathSeparator
./ -> ""

Posix:   normalise "/file/\\test////" == "/file/\\test/"
Posix:   normalise "/file/./test" == "/file/test"
Posix:   normalise "/test/file/../bob/fred/" == "/test/file/../bob/fred/"
Posix:   normalise "../bob/fred/" == "../bob/fred/"
Posix:   normalise "./bob/fred/" == "bob/fred/"
Windows: normalise "c:\\file/bob\\" == "C:\\file\\bob\\"
Windows: normalise "c:\\" == "C:\\"
Windows: normalise "C:.\\" == "C:"
Windows: normalise "\\\\server\\test" == "\\\\server\\test"
Windows: normalise "//server/test" == "\\\\server\\test"
Windows: normalise "c:/file" == "C:\\file"
Windows: normalise "/file" == "\\file"
Windows: normalise "\\" == "\\"
Windows: normalise "/./" == "\\"
         normalise "." == "."
Posix:   normalise "./" == "./"
Posix:   normalise "./." == "./"
Posix:   normalise "/./" == "/"
Posix:   normalise "/" == "/"
Posix:   normalise "bob/fred/." == "bob/fred/"
Posix:   normalise "//home" == "/home"

equalFilePath :: FilePath -> FilePath -> Bool Source

Equality of two FilePaths. If you call System.Directory.canonicalizePath first this has a much better chance of working. Note that this doesn't follow symlinks or DOSNAM~1s.

         x == y ==> equalFilePath x y
         normalise x == normalise y ==> equalFilePath x y
         equalFilePath "foo" "foo/"
         not (equalFilePath "foo" "/foo")
Posix:   not (equalFilePath "foo" "FOO")
Windows: equalFilePath "foo" "FOO"
Windows: not (equalFilePath "C:" "C:/")

makeRelative :: FilePath -> FilePath -> FilePath Source

Contract a filename, based on a relative path.

The corresponding makeAbsolute function can be found in System.Directory.

         makeRelative "/directory" "/directory/file.ext" == "file.ext"
         Valid x => makeRelative (takeDirectory x) x `equalFilePath` takeFileName x
         makeRelative x x == "."
         Valid x y => equalFilePath x y || (isRelative x && makeRelative y x == x) || equalFilePath (y </> makeRelative y x) x
Windows: makeRelative "C:\\Home" "c:\\home\\bob" == "bob"
Windows: makeRelative "C:\\Home" "c:/home/bob" == "bob"
Windows: makeRelative "C:\\Home" "D:\\Home\\Bob" == "D:\\Home\\Bob"
Windows: makeRelative "C:\\Home" "C:Home\\Bob" == "C:Home\\Bob"
Windows: makeRelative "/Home" "/home/bob" == "bob"
Windows: makeRelative "/" "//" == "//"
Posix:   makeRelative "/Home" "/home/bob" == "/home/bob"
Posix:   makeRelative "/home/" "/home/bob/foo/bar" == "bob/foo/bar"
Posix:   makeRelative "/fred" "bob" == "bob"
Posix:   makeRelative "/file/test" "/file/test/fred" == "fred"
Posix:   makeRelative "/file/test" "/file/test/fred/" == "fred/"
Posix:   makeRelative "some/path" "some/path/a/b/c" == "a/b/c"

isRelative :: FilePath -> Bool Source

Is a path relative, or is it fixed to the root?

Windows: isRelative "path\\test" == True
Windows: isRelative "c:\\test" == False
Windows: isRelative "c:test" == True
Windows: isRelative "c:\\" == False
Windows: isRelative "c:/" == False
Windows: isRelative "c:" == True
Windows: isRelative "\\\\foo" == False
Windows: isRelative "\\\\?\\foo" == False
Windows: isRelative "\\\\?\\UNC\\foo" == False
Windows: isRelative "/foo" == True
Windows: isRelative "\\foo" == True
Posix:   isRelative "test/path" == True
Posix:   isRelative "/test" == False
Posix:   isRelative "/" == False

According to [1]:

"A UNC name of any format [is never relative]."
"You cannot use the "\?" prefix with a relative path."

isAbsolute :: FilePath -> Bool Source

not . isRelative

isAbsolute x == not (isRelative x)

isValid :: FilePath -> Bool Source

Is a FilePath valid, i.e. could you create a file like it?

         isValid "" == False
Posix:   isValid "/random_ path:*" == True
Posix:   isValid x == not (null x)
Windows: isValid "c:\\test" == True
Windows: isValid "c:\\test:of_test" == False
Windows: isValid "test*" == False
Windows: isValid "c:\\test\\nul" == False
Windows: isValid "c:\\test\\prn.txt" == False
Windows: isValid "c:\\nul\\file" == False
Windows: isValid "\\\\" == False
Windows: isValid "\\\\\\foo" == False
Windows: isValid "\\\\?\\D:file" == False

makeValid :: FilePath -> FilePath Source

Take a FilePath and make it valid; does not change already valid FilePaths.

isValid (makeValid x)
isValid x ==> makeValid x == x
makeValid "" == "_"
Windows: makeValid "c:\\already\\/valid" == "c:\\already\\/valid"
Windows: makeValid "c:\\test:of_test" == "c:\\test_of_test"
Windows: makeValid "test*" == "test_"
Windows: makeValid "c:\\test\\nul" == "c:\\test\\nul_"
Windows: makeValid "c:\\test\\prn.txt" == "c:\\test\\prn_.txt"
Windows: makeValid "c:\\test/prn.txt" == "c:\\test/prn_.txt"
Windows: makeValid "c:\\nul\\file" == "c:\\nul_\\file"
Windows: makeValid "\\\\\\foo" == "\\\\drive"
Windows: makeValid "\\\\?\\D:file" == "\\\\?\\D:\\file"