1 // Copyright 2009 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
5 // Package filepath implements utility routines for manipulating filename paths
6 // in a way compatible with the target operating system-defined file paths.
16 // A lazybuf is a lazily constructed path buffer.
17 // It supports append, reading previously appended bytes,
18 // and retrieving the final string. It does not allocate a buffer
19 // to hold the output until that output diverges from s.
28 func (b *lazybuf) index(i int) byte {
35 func (b *lazybuf) append(c byte) {
37 if b.w < len(b.path) && b.path[b.w] == c {
41 b.buf = make([]byte, len(b.path))
42 copy(b.buf, b.path[:b.w])
48 func (b *lazybuf) string() string {
50 return b.volAndPath[:b.volLen+b.w]
52 return b.volAndPath[:b.volLen] + string(b.buf[:b.w])
56 Separator = os.PathSeparator
57 ListSeparator = os.PathListSeparator
60 // Clean returns the shortest path name equivalent to path
61 // by purely lexical processing. It applies the following rules
62 // iteratively until no further processing can be done:
64 // 1. Replace multiple Separator elements with a single one.
65 // 2. Eliminate each . path name element (the current directory).
66 // 3. Eliminate each inner .. path name element (the parent directory)
67 // along with the non-.. element that precedes it.
68 // 4. Eliminate .. elements that begin a rooted path:
69 // that is, replace "/.." by "/" at the beginning of a path,
70 // assuming Separator is '/'.
72 // The returned path ends in a slash only if it represents a root directory,
73 // such as "/" on Unix or `C:\` on Windows.
75 // If the result of this process is an empty string, Clean
76 // returns the string ".".
78 // See also Rob Pike, ``Lexical File Names in Plan 9 or
79 // Getting Dot-Dot Right,''
80 // http://plan9.bell-labs.com/sys/doc/lexnames.html
81 func Clean(path string) string {
83 volLen := volumeNameLen(path)
86 if volLen > 1 && originalPath[1] != ':' {
88 return FromSlash(originalPath)
90 return originalPath + "."
92 rooted := os.IsPathSeparator(path[0])
95 // reading from path; r is index of next byte to process.
96 // writing to buf; w is index of next byte to write.
97 // dotdot is index in buf where .. must stop, either because
98 // it is the leading slash or it is a leading ../../.. prefix.
100 out := lazybuf{path: path, volAndPath: originalPath, volLen: volLen}
103 out.append(Separator)
109 case os.IsPathSeparator(path[r]):
110 // empty path element
112 case path[r] == '.' && (r+1 == n || os.IsPathSeparator(path[r+1])):
115 case path[r] == '.' && path[r+1] == '.' && (r+2 == n || os.IsPathSeparator(path[r+2])):
116 // .. element: remove to last separator
122 for out.w > dotdot && !os.IsPathSeparator(out.index(out.w)) {
126 // cannot backtrack, but not rooted, so append .. element.
128 out.append(Separator)
135 // real path element.
136 // add slash if needed
137 if rooted && out.w != 1 || !rooted && out.w != 0 {
138 out.append(Separator)
141 for ; r < n && !os.IsPathSeparator(path[r]); r++ {
147 // Turn empty string into "."
152 return FromSlash(out.string())
155 // ToSlash returns the result of replacing each separator character
156 // in path with a slash ('/') character. Multiple separators are
157 // replaced by multiple slashes.
158 func ToSlash(path string) string {
159 if Separator == '/' {
162 return strings.Replace(path, string(Separator), "/", -1)
165 // FromSlash returns the result of replacing each slash ('/') character
166 // in path with a separator character. Multiple slashes are replaced
167 // by multiple separators.
168 func FromSlash(path string) string {
169 if Separator == '/' {
172 return strings.Replace(path, "/", string(Separator), -1)
175 // SplitList splits a list of paths joined by the OS-specific ListSeparator,
176 // usually found in PATH or GOPATH environment variables.
177 // Unlike strings.Split, SplitList returns an empty slice when passed an empty string.
178 func SplitList(path string) []string {
179 return splitList(path)
182 // Split splits path immediately following the final Separator,
183 // separating it into a directory and file name component.
184 // If there is no Separator in path, Split returns an empty dir
185 // and file set to path.
186 // The returned values have the property that path = dir+file.
187 func Split(path string) (dir, file string) {
188 vol := VolumeName(path)
190 for i >= len(vol) && !os.IsPathSeparator(path[i]) {
193 return path[:i+1], path[i+1:]
196 // Join joins any number of path elements into a single path, adding
197 // a Separator if necessary. The result is Cleaned, in particular
198 // all empty strings are ignored.
199 func Join(elem ...string) string {
200 for i, e := range elem {
202 return Clean(strings.Join(elem[i:], string(Separator)))
208 // Ext returns the file name extension used by path.
209 // The extension is the suffix beginning at the final dot
210 // in the final element of path; it is empty if there is
212 func Ext(path string) string {
213 for i := len(path) - 1; i >= 0 && !os.IsPathSeparator(path[i]); i-- {
221 // EvalSymlinks returns the path name after the evaluation of any symbolic
223 // If path is relative the result will be relative to the current directory,
224 // unless one of the components is an absolute symbolic link.
225 func EvalSymlinks(path string) (string, error) {
226 return evalSymlinks(path)
229 // Abs returns an absolute representation of path.
230 // If the path is not absolute it will be joined with the current
231 // working directory to turn it into an absolute path. The absolute
232 // path name for a given file is not guaranteed to be unique.
233 func Abs(path string) (string, error) {
237 func unixAbs(path string) (string, error) {
239 return Clean(path), nil
241 wd, err := os.Getwd()
245 return Join(wd, path), nil
248 // Rel returns a relative path that is lexically equivalent to targpath when
249 // joined to basepath with an intervening separator. That is,
250 // Join(basepath, Rel(basepath, targpath)) is equivalent to targpath itself.
251 // On success, the returned path will always be relative to basepath,
252 // even if basepath and targpath share no elements.
253 // An error is returned if targpath can't be made relative to basepath or if
254 // knowing the current working directory would be necessary to compute it.
255 func Rel(basepath, targpath string) (string, error) {
256 baseVol := VolumeName(basepath)
257 targVol := VolumeName(targpath)
258 base := Clean(basepath)
259 targ := Clean(targpath)
263 base = base[len(baseVol):]
264 targ = targ[len(targVol):]
268 // Can't use IsAbs - `\a` and `a` are both relative in Windows.
269 baseSlashed := len(base) > 0 && base[0] == Separator
270 targSlashed := len(targ) > 0 && targ[0] == Separator
271 if baseSlashed != targSlashed || baseVol != targVol {
272 return "", errors.New("Rel: can't make " + targ + " relative to " + base)
274 // Position base[b0:bi] and targ[t0:ti] at the first differing elements.
277 var b0, bi, t0, ti int
279 for bi < bl && base[bi] != Separator {
282 for ti < tl && targ[ti] != Separator {
285 if targ[t0:ti] != base[b0:bi] {
297 if base[b0:bi] == ".." {
298 return "", errors.New("Rel: can't make " + targ + " relative to " + base)
301 // Base elements left. Must go up before going down.
302 seps := strings.Count(base[b0:bl], string(Separator))
307 buf := make([]byte, size)
309 for i := 0; i < seps; i++ {
311 copy(buf[n+1:], "..")
316 copy(buf[n+1:], targ[t0:])
318 return string(buf), nil
320 return targ[t0:], nil
323 // SkipDir is used as a return value from WalkFuncs to indicate that
324 // the directory named in the call is to be skipped. It is not returned
325 // as an error by any function.
326 var SkipDir = errors.New("skip this directory")
328 // WalkFunc is the type of the function called for each file or directory
329 // visited by Walk. The path argument contains the argument to Walk as a
330 // prefix; that is, if Walk is called with "dir", which is a directory
331 // containing the file "a", the walk function will be called with argument
332 // "dir/a". The info argument is the os.FileInfo for the named path.
334 // If there was a problem walking to the file or directory named by path, the
335 // incoming error will describe the problem and the function can decide how
336 // to handle that error (and Walk will not descend into that directory). If
337 // an error is returned, processing stops. The sole exception is that if path
338 // is a directory and the function returns the special value SkipDir, the
339 // contents of the directory are skipped and processing continues as usual on
341 type WalkFunc func(path string, info os.FileInfo, err error) error
343 var lstat = os.Lstat // for testing
345 // walk recursively descends path, calling w.
346 func walk(path string, info os.FileInfo, walkFn WalkFunc) error {
347 err := walkFn(path, info, nil)
349 if info.IsDir() && err == SkipDir {
359 names, err := readDirNames(path)
361 return walkFn(path, info, err)
364 for _, name := range names {
365 filename := Join(path, name)
366 fileInfo, err := lstat(filename)
368 if err := walkFn(filename, fileInfo, err); err != nil && err != SkipDir {
372 err = walk(filename, fileInfo, walkFn)
374 if !fileInfo.IsDir() || err != SkipDir {
383 // Walk walks the file tree rooted at root, calling walkFn for each file or
384 // directory in the tree, including root. All errors that arise visiting files
385 // and directories are filtered by walkFn. The files are walked in lexical
386 // order, which makes the output deterministic but means that for very
387 // large directories Walk can be inefficient.
388 // Walk does not follow symbolic links.
389 func Walk(root string, walkFn WalkFunc) error {
390 info, err := os.Lstat(root)
392 return walkFn(root, nil, err)
394 return walk(root, info, walkFn)
397 // readDirNames reads the directory named by dirname and returns
398 // a sorted list of directory entries.
399 func readDirNames(dirname string) ([]string, error) {
400 f, err := os.Open(dirname)
404 names, err := f.Readdirnames(-1)
413 // Base returns the last element of path.
414 // Trailing path separators are removed before extracting the last element.
415 // If the path is empty, Base returns ".".
416 // If the path consists entirely of separators, Base returns a single separator.
417 func Base(path string) string {
421 // Strip trailing slashes.
422 for len(path) > 0 && os.IsPathSeparator(path[len(path)-1]) {
423 path = path[0 : len(path)-1]
425 // Throw away volume name
426 path = path[len(VolumeName(path)):]
427 // Find the last element
429 for i >= 0 && !os.IsPathSeparator(path[i]) {
435 // If empty now, it had only slashes.
437 return string(Separator)
442 // Dir returns all but the last element of path, typically the path's directory.
443 // After dropping the final element, the path is Cleaned and trailing
444 // slashes are removed.
445 // If the path is empty, Dir returns ".".
446 // If the path consists entirely of separators, Dir returns a single separator.
447 // The returned path does not end in a separator unless it is the root directory.
448 func Dir(path string) string {
449 vol := VolumeName(path)
451 for i >= len(vol) && !os.IsPathSeparator(path[i]) {
454 dir := Clean(path[len(vol) : i+1])
458 // VolumeName returns leading volume name.
459 // Given "C:\foo\bar" it returns "C:" under windows.
460 // Given "\\host\share\foo" it returns "\\host\share".
461 // On other platforms it returns "".
462 func VolumeName(path string) (v string) {
463 return path[:volumeNameLen(path)]