filepath-1.4.2.2: Library for manipulating FilePaths in a cross platform way.
Copyright(c) Neil Mitchell 2005-2014
LicenseBSD3
Maintainerndmitchell@gmail.com
Stabilitystable
Portabilityportable
Safe HaskellSafe
LanguageHaskell2010

System.FilePath

Description

A library for FilePath manipulations, using Posix or Windows filepaths depending on the platform.

Both System.FilePath.Posix and System.FilePath.Windows provide the same interface.

Given the example FilePath: /directory/file.ext

We can use the following functions to extract pieces.

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.Directory.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. Blank items are ignored on Windows, and converted to . on Posix. On Windows path elements are stripped of quotes.

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"
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"

replaceExtensions :: FilePath -> String -> FilePath Source #

Replace all extensions of a file with a new extension. Note that replaceExtension and addExtension both work for adding multiple extensions, so only required when you need to drop all extensions first.

replaceExtensions "file.fred.bob" "txt" == "file.txt"
replaceExtensions "file.fred.bob" "tar.gz" == "file.tar.gz"

isExtensionOf :: String -> FilePath -> Bool Source #

Does the given filename have the specified extension?

"png" `isExtensionOf` "/directory/file.png" == True
".png" `isExtensionOf` "/directory/file.png" == True
".tar.gz" `isExtensionOf` "bar/foo.tar.gz" == True
"ar.gz" `isExtensionOf` "bar/foo.tar.gz" == False
"png" `isExtensionOf` "/directory/file.png.jpg" == False
"csv/table.csv" `isExtensionOf` "/data/csv/table.csv" == False

stripExtension :: String -> FilePath -> Maybe FilePath Source #

Drop the given extension from a FilePath, and the "." preceding it. Returns Nothing if the FilePath does not have the given extension, or Just and the part before the extension if it does.

This function can be more predictable than dropExtensions, especially if the filename might itself contain . characters.

stripExtension "hs.o" "foo.x.hs.o" == Just "foo.x"
stripExtension "hi.o" "foo.x.hs.o" == Nothing
dropExtension x == fromJust (stripExtension (takeExtension x) x)
dropExtensions x == fromJust (stripExtension (takeExtensions x) x)
stripExtension ".c.d" "a.b.c.d"  == Just "a.b"
stripExtension ".c.d" "a.b..c.d" == Just "a.b."
stripExtension "baz"  "foo.bar"  == Nothing
stripExtension "bar"  "foobar"   == Nothing
stripExtension ""     x          == Just x

Filename/directory functions

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

Split a filename into directory and file. </> 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 #

An alias for </>.

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

Combine two paths with a path separator. If the second path starts with a path separator or a drive letter, then it returns the second. The intention is that readFile (dir </> file) will access the same file as setCurrentDirectory dir; readFile file.

Posix:   "/directory" </> "file.ext" == "/directory/file.ext"
Windows: "/directory" </> "file.ext" == "/directory\\file.ext"
         "directory" </> "/file.ext" == "/file.ext"
Valid x => (takeDirectory x </> takeFileName x) `equalFilePath` x

Combined:

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

Not combined:

Posix:   "home" </> "/bob" == "/bob"
Windows: "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 </> is to never combine these forms.

Windows: "home" </> "/bob" == "/bob"
Windows: "home" </> "\\bob" == "\\bob"
Windows: "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 </> is to never combine these forms.

Windows: "D:\\foo" </> "C:bar" == "C:bar"
Windows: "C:\\foo" </> "C:bar" == "C:bar"

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 a == foldr (</>) "" a
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
  • ./ -> ""

Does not remove "..", because of symlinks.

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 "/a/../c" == "/a/../c"
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.

Similar to normalise, this does not expand "..", because of symlinks.

         x == y ==> equalFilePath x y
         normalise x == normalise y ==> equalFilePath x y
         equalFilePath "foo" "foo/"
         not (equalFilePath "/a/../c" "/c")
         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. Note that the resulting path will never introduce .. paths, as the presence of symlinks means ../b may not reach a/b if it starts from a/c. For a worked example see this blog post.

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? This function checks for invalid names, and invalid characters, but does not check if length limits are exceeded, as these are typically filesystem dependent.

         isValid "" == False
         isValid "\0" == 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
Windows: isValid "foo\tbar" == False
Windows: isValid "nul .txt" == False
Windows: isValid " nul.txt" == True

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 "" == "_"
makeValid "file\0name" == "file_name"
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"
Windows: makeValid "nul .txt" == "nul _.txt"