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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// The path package implements utility routines for manipulating
// slash-separated filename paths.
package path
import (
"strings"
)
// Clean returns the shortest path name equivalent to path
// by purely lexical processing. It applies the following rules
// iteratively until no further processing can be done:
//
// 1. Replace multiple slashes with a single slash.
// 2. Eliminate each . path name element (the current directory).
// 3. Eliminate each inner .. path name element (the parent directory)
// along with the non-.. element that precedes it.
// 4. Eliminate .. elements that begin a rooted path:
// that is, replace "/.." by "/" at the beginning of a path.
//
// If the result of this process is an empty string, Clean
// returns the string ".".
//
// See also Rob Pike, ``Lexical File Names in Plan 9 or
// Getting Dot-Dot right,''
// http://plan9.bell-labs.com/sys/doc/lexnames.html
func Clean(path string) string {
if path == "" {
return "."
}
rooted := path[0] == '/'
n := len(path)
// Invariants:
// reading from path; r is index of next byte to process.
// writing to buf; w is index of next byte to write.
// dotdot is index in buf where .. must stop, either because
// it is the leading slash or it is a leading ../../.. prefix.
buf := []byte(path)
r, w, dotdot := 0, 0, 0
if rooted {
r, w, dotdot = 1, 1, 1
}
for r < n {
switch {
case path[r] == '/':
// empty path element
r++
case path[r] == '.' && (r+1 == n || path[r+1] == '/'):
// . element
r++
case path[r] == '.' && path[r+1] == '.' && (r+2 == n || path[r+2] == '/'):
// .. element: remove to last /
r += 2
switch {
case w > dotdot:
// can backtrack
w--
for w > dotdot && buf[w] != '/' {
w--
}
case !rooted:
// cannot backtrack, but not rooted, so append .. element.
if w > 0 {
buf[w] = '/'
w++
}
buf[w] = '.'
w++
buf[w] = '.'
w++
dotdot = w
}
default:
// real path element.
// add slash if needed
if rooted && w != 1 || !rooted && w != 0 {
buf[w] = '/'
w++
}
// copy element
for ; r < n && path[r] != '/'; r++ {
buf[w] = path[r]
w++
}
}
}
// Turn empty string into "."
if w == 0 {
buf[w] = '.'
w++
}
return string(buf[0:w])
}
// Split splits path immediately following the final path separator,
// separating it into a directory and file name component.
// If there is no separator in path, Split returns an empty dir and
// file set to path.
func Split(path string) (dir, file string) {
i := strings.LastIndex(path, "/")
return path[:i+1], path[i+1:]
}
// Join joins any number of path elements into a single path, adding a
// separating slash if necessary. All empty strings are ignored.
func Join(elem ...string) string {
for i, e := range elem {
if e != "" {
return Clean(strings.Join(elem[i:], "/"))
}
}
return ""
}
// Ext returns the file name extension used by path.
// The extension is the suffix beginning at the final dot
// in the final slash-separated element of path;
// it is empty if there is no dot.
func Ext(path string) string {
for i := len(path) - 1; i >= 0 && path[i] != '/'; i-- {
if path[i] == '.' {
return path[i:]
}
}
return ""
}
// Base returns the last element of path.
// Trailing slashes are removed before extracting the last element.
// If the path is empty, Base returns ".".
// If the path consists entirely of slashes, Base returns "/".
func Base(path string) string {
if path == "" {
return "."
}
// Strip trailing slashes.
for len(path) > 0 && path[len(path)-1] == '/' {
path = path[0 : len(path)-1]
}
// Find the last element
if i := strings.LastIndex(path, "/"); i >= 0 {
path = path[i+1:]
}
// If empty now, it had only slashes.
if path == "" {
return "/"
}
return path
}
// IsAbs returns true if the path is absolute.
func IsAbs(path string) bool {
return len(path) > 0 && path[0] == '/'
}
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