System.OsPath.Posix

Types

data PosixString

Commonly used Posix string as uninterpreted char[] array.

Instances

Monoid PosixString

Defined in System.OsString.Internal.Types

Methods

mempty :: PosixString

mappend :: PosixString -> PosixString -> PosixString

mconcat :: [PosixString] -> PosixString

Semigroup PosixString

Defined in System.OsString.Internal.Types

Methods

(<>) :: PosixString -> PosixString -> PosixString

sconcat :: NonEmpty PosixString -> PosixString

stimes :: Integral b => b -> PosixString -> PosixString

Generic PosixString

Defined in System.OsString.Internal.Types

Associated Types

type Rep PosixString

Defined in System.OsString.Internal.Types

type Rep PosixString = D1 ('MetaData "PosixString" "System.OsString.Internal.Types" "os-string-2.0.4-ea6ae28dc9b3712b976bf1323571bc0315dcdcc7322fe276e2a2c12e62d6c267" 'True) (C1 ('MetaCons "PosixString" 'PrefixI 'True) (S1 ('MetaSel ('Just "getPosixString") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 ShortByteString)))

Methods

from :: PosixString -> Rep PosixString x

to :: Rep PosixString x -> PosixString

Show PosixString

Prints the raw bytes without decoding.

Defined in System.OsString.Internal.Types

Methods

showsPrec :: Int -> PosixString -> ShowS

show :: PosixString -> String

showList :: [PosixString] -> ShowS

NFData PosixString

Defined in System.OsString.Internal.Types

Methods

rnf :: PosixString -> ()

Eq PosixString

Defined in System.OsString.Internal.Types

Methods

(==) :: PosixString -> PosixString -> Bool

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

Ord PosixString

Defined in System.OsString.Internal.Types

Methods

compare :: PosixString -> PosixString -> Ordering

(<) :: PosixString -> PosixString -> Bool

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

(>) :: PosixString -> PosixString -> Bool

(>=) :: PosixString -> PosixString -> Bool

max :: PosixString -> PosixString -> PosixString

min :: PosixString -> PosixString -> PosixString

Lift PosixString

Defined in System.OsString.Internal.Types

Methods

lift :: Quote m => PosixString -> m Exp

liftTyped :: forall (m :: Type -> Type). Quote m => PosixString -> Code m PosixString

type Rep PosixString

Defined in System.OsString.Internal.Types

type Rep PosixString = D1 ('MetaData "PosixString" "System.OsString.Internal.Types" "os-string-2.0.4-ea6ae28dc9b3712b976bf1323571bc0315dcdcc7322fe276e2a2c12e62d6c267" 'True) (C1 ('MetaCons "PosixString" 'PrefixI 'True) (S1 ('MetaSel ('Just "getPosixString") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 ShortByteString)))

data PosixChar

Instances

Generic PosixChar

Defined in System.OsString.Internal.Types

Associated Types

type Rep PosixChar

Defined in System.OsString.Internal.Types

type Rep PosixChar = D1 ('MetaData "PosixChar" "System.OsString.Internal.Types" "os-string-2.0.4-ea6ae28dc9b3712b976bf1323571bc0315dcdcc7322fe276e2a2c12e62d6c267" 'True) (C1 ('MetaCons "PosixChar" 'PrefixI 'True) (S1 ('MetaSel ('Just "getPosixChar") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 Word8)))

Methods

from :: PosixChar -> Rep PosixChar x

to :: Rep PosixChar x -> PosixChar

Show PosixChar

Defined in System.OsString.Internal.Types

Methods

showsPrec :: Int -> PosixChar -> ShowS

show :: PosixChar -> String

showList :: [PosixChar] -> ShowS

NFData PosixChar

Defined in System.OsString.Internal.Types

Methods

rnf :: PosixChar -> ()

Eq PosixChar

Defined in System.OsString.Internal.Types

Methods

(==) :: PosixChar -> PosixChar -> Bool

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

Ord PosixChar

Defined in System.OsString.Internal.Types

Methods

compare :: PosixChar -> PosixChar -> Ordering

(<) :: PosixChar -> PosixChar -> Bool

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

(>) :: PosixChar -> PosixChar -> Bool

(>=) :: PosixChar -> PosixChar -> Bool

max :: PosixChar -> PosixChar -> PosixChar

min :: PosixChar -> PosixChar -> PosixChar

type Rep PosixChar

Defined in System.OsString.Internal.Types

type Rep PosixChar = D1 ('MetaData "PosixChar" "System.OsString.Internal.Types" "os-string-2.0.4-ea6ae28dc9b3712b976bf1323571bc0315dcdcc7322fe276e2a2c12e62d6c267" 'True) (C1 ('MetaCons "PosixChar" 'PrefixI 'True) (S1 ('MetaSel ('Just "getPosixChar") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 Word8)))

type PosixPath = PosixString

Filepaths are char[] data on unix as passed to syscalls.

Filepath construction

encodeUtf :: MonadThrow m => String -> m PosixString

Partial unicode friendly encoding.

This encodes as UTF8 (strictly), which is a good guess.

Throws an EncodingException if encoding fails. If the input does not contain surrogate chars, you can use unsafeEncodeUtf.

unsafeEncodeUtf :: HasCallStack => String -> PosixString

Unsafe unicode friendly encoding.

Like encodeUtf, except it crashes when the input contains surrogate chars. For sanitized input, this can be useful.

encodeWith :: TextEncoding -> String -> Either EncodingException PosixString

Encode a String with the specified encoding.

encodeFS :: String -> IO PosixPath

pstr :: QuasiQuoter

QuasiQuote a PosixPath. This accepts Unicode characters and encodes as UTF-8. Runs isValid on the input.

pack :: [PosixChar] -> PosixString

Pack a list of platform words to a platform string.

Note that using this in conjunction with unsafeFromChar to convert from [Char] to platform string is probably not what you want, because it will truncate unicode code points.

Filepath deconstruction

decodeUtf :: MonadThrow m => PosixString -> m String

Partial unicode friendly decoding.

This decodes as UTF8 (strictly), which is a good guess. Note that filenames on unix are encoding agnostic char arrays.

Throws a EncodingException if decoding fails.

decodeWith :: TextEncoding -> PosixString -> Either EncodingException String

Decode a PosixString with the specified encoding.

The String is forced into memory to catch all exceptions.

decodeFS :: PosixPath -> IO String

unpack :: PosixString -> [PosixChar]

Unpack a platform string to a list of platform words.

Word construction

unsafeFromChar :: Char -> PosixChar

Truncates to 1 octet.

Word deconstruction

toChar :: PosixChar -> Char

Converts back to a unicode codepoint (total).

Separator predicates

pathSeparator :: PosixChar

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

pathSeparator ==  '/'

pathSeparators :: [PosixChar]

The list of all possible separators.

pathSeparators == ['/']
pathSeparator `elem` pathSeparators

isPathSeparator :: PosixChar -> Bool

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

isPathSeparator a == (a `elem` pathSeparators)

searchPathSeparator :: PosixChar

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

searchPathSeparator == ':'

isSearchPathSeparator :: PosixChar -> Bool

Is the character a file separator?

isSearchPathSeparator a == (a == searchPathSeparator)

extSeparator :: PosixChar

File extension character

extSeparator == '.'

isExtSeparator :: PosixChar -> Bool

Is the character an extension character?

isExtSeparator a == (a == extSeparator)

$PATH methods

splitSearchPath :: PosixString -> [PosixPath]

Take a string, split it on the searchPathSeparator character.

Blank items are converted to . on , and quotes are not treated specially.

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

splitSearchPath "File1:File2:File3"  == ["File1","File2","File3"]
splitSearchPath "File1::File2:File3" == ["File1",".","File2","File3"]

Extension functions

splitExtension :: PosixPath -> (PosixPath, PosixString)

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 :: PosixPath -> PosixString

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 :: PosixPath -> PosixString -> PosixPath

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

(-<.>) :: PosixPath -> PosixString -> PosixPath

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 :: PosixPath -> PosixPath

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

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

addExtension :: PosixPath -> PosixString -> PosixPath

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"

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"

hasExtension :: PosixPath -> Bool

Does the given filename have an extension?

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

(<.>) :: PosixPath -> PosixString -> PosixPath

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 :: PosixPath -> (PosixPath, PosixString)

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 :: PosixPath -> PosixPath

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 :: PosixPath -> PosixString

Get all extensions.

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

replaceExtensions :: PosixPath -> PosixString -> PosixPath

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 :: PosixString -> PosixPath -> Bool

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 :: PosixString -> PosixPath -> Maybe PosixPath

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 :: PosixPath -> (PosixPath, PosixPath)

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")
splitFileName "/" == ("/","")

takeFileName :: PosixPath -> PosixPath

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 :: PosixPath -> PosixString -> PosixPath

Set the filename.

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

dropFileName :: PosixPath -> PosixPath

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 :: PosixPath -> PosixPath

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 :: PosixPath -> PosixString -> PosixPath

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 :: PosixPath -> PosixPath

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"

replaceDirectory :: PosixPath -> PosixPath -> PosixPath

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 :: PosixPath -> PosixPath -> PosixPath

An alias for </>.

(</>) :: PosixPath -> PosixPath -> PosixPath

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.

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

Combined:

"/" </> "test" == "/test"
"home" </> "bob" == "home/bob"
"x:" </> "foo" == "x:/foo"

Not combined:

"home" </> "/bob" == "/bob"

splitPath :: PosixPath -> [PosixPath]

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 "" == []
splitPath "/file/test" == ["/","file/","test"]

joinPath :: [PosixPath] -> PosixPath

Join path elements back together.

joinPath z == foldr (</>) "" z
joinPath ["/","directory/","file.ext"] == "/directory/file.ext"
Valid x => joinPath (splitPath x) == x
joinPath [] == ""
joinPath ["test","file","path"] == "test/file/path"

splitDirectories :: PosixPath -> [PosixPath]

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"]
Valid x => joinPath (splitDirectories x) `equalFilePath` x
splitDirectories "" == []
splitDirectories "/test///file" == ["/","test","file"]

Drive functions

splitDrive :: PosixPath -> (PosixPath, PosixPath)

Split a path into a drive and a path. / is a Drive.

uncurry (<>) (splitDrive x) == x
splitDrive "/test" == ("/","test")
splitDrive "//test" == ("//","test")
splitDrive "test/file" == ("","test/file")
splitDrive "file" == ("","file")

joinDrive :: PosixPath -> PosixPath -> PosixPath

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"

Join a drive and the rest of the path.

Valid x => uncurry joinDrive (splitDrive x) == x

takeDrive :: PosixPath -> PosixPath

Get the drive from a filepath.

takeDrive x == fst (splitDrive x)

hasDrive :: PosixPath -> Bool

Does a path have a drive.

not (hasDrive x) == null (takeDrive x)
hasDrive "/foo" == True
hasDrive "foo" == False
hasDrive "" == False

dropDrive :: PosixPath -> PosixPath

Delete the drive, if it exists.

dropDrive x == snd (splitDrive x)

isDrive :: PosixPath -> Bool

Is an element a drive

isDrive "/" == True
isDrive "/foo" == False
isDrive "" == False

Trailing slash functions

hasTrailingPathSeparator :: PosixPath -> Bool

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

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

addTrailingPathSeparator :: PosixPath -> PosixPath

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

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

dropTrailingPathSeparator :: PosixPath -> PosixPath

Remove any trailing path separators

dropTrailingPathSeparator "file/test/" == "file/test"
dropTrailingPathSeparator "/" == "/"
not (hasTrailingPathSeparator (dropTrailingPathSeparator x)) || isDrive x

File name manipulations

normalise :: PosixPath -> PosixPath

Normalise a file

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

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

normalise "/file/\\test////" == "/file/\\test/"
normalise "/file/./test" == "/file/test"
normalise "/test/file/../bob/fred/" == "/test/file/../bob/fred/"
normalise "../bob/fred/" == "../bob/fred/"
normalise "/a/../c" == "/a/../c"
normalise "./bob/fred/" == "bob/fred/"
normalise "." == "."
normalise "./" == "./"
normalise "./." == "./"
normalise "/./" == "/"
normalise "/" == "/"
normalise "bob/fred/." == "bob/fred/"
normalise "//home" == "/home"

equalFilePath :: PosixPath -> PosixPath -> Bool

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")
not (equalFilePath "foo" "FOO")

makeRelative :: PosixPath -> PosixPath -> PosixPath

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
makeRelative "/Home" "/home/bob" == "/home/bob"
makeRelative "/home/" "/home/bob/foo/bar" == "bob/foo/bar"
makeRelative "/fred" "bob" == "bob"
makeRelative "/file/test" "/file/test/fred" == "fred"
makeRelative "/file/test" "/file/test/fred/" == "fred/"
makeRelative "some/path" "some/path/a/b/c" == "a/b/c"

isRelative :: PosixPath -> Bool

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

isRelative "test/path" == True
isRelative "/test" == False
isRelative "/" == False

isAbsolute :: PosixPath -> Bool

not . isRelative

isAbsolute x == not (isRelative x)

isValid :: PosixPath -> Bool

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
isValid "/random_ path:*" == True
isValid x == not (null x)

makeValid :: PosixPath -> PosixPath

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"