// 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. package os import ( "runtime" "sync" "syscall" ) var getwdCache struct { sync.Mutex dir string } // Getwd returns a rooted path name corresponding to the // current directory. If the current directory can be // reached via multiple paths (due to symbolic links), // Getwd may return any one of them. func Getwd() (dir string, err error) { if runtime.GOOS == "windows" || runtime.GOOS == "plan9" { return syscall.Getwd() } // Clumsy but widespread kludge: // if $PWD is set and matches ".", use it. dot, err := statNolog(".") if err != nil { return "", err } dir = Getenv("PWD") if len(dir) > 0 && dir[0] == '/' { d, err := statNolog(dir) if err == nil && SameFile(dot, d) { return dir, nil } } // If the operating system provides a Getwd call, use it. // Otherwise, we're trying to find our way back to ".". if syscall.ImplementsGetwd { var ( s string e error ) for { s, e = syscall.Getwd() if e != syscall.EINTR { break } } return s, NewSyscallError("getwd", e) } // Apply same kludge but to cached dir instead of $PWD. getwdCache.Lock() dir = getwdCache.dir getwdCache.Unlock() if len(dir) > 0 { d, err := statNolog(dir) if err == nil && SameFile(dot, d) { return dir, nil } } // Root is a special case because it has no parent // and ends in a slash. root, err := statNolog("/") if err != nil { // Can't stat root - no hope. return "", err } if SameFile(root, dot) { return "/", nil } // General algorithm: find name in parent // and then find name of parent. Each iteration // adds /name to the beginning of dir. dir = "" for parent := ".."; ; parent = "../" + parent { if len(parent) >= 1024 { // Sanity check return "", syscall.ENAMETOOLONG } fd, err := openFileNolog(parent, O_RDONLY, 0) if err != nil { return "", err } for { names, err := fd.Readdirnames(100) if err != nil { fd.Close() return "", err } for _, name := range names { d, _ := lstatNolog(parent + "/" + name) if SameFile(d, dot) { dir = "/" + name + dir goto Found } } } Found: pd, err := fd.Stat() fd.Close() if err != nil { return "", err } if SameFile(pd, root) { break } // Set up for next round. dot = pd } // Save answer as hint to avoid the expensive path next time. getwdCache.Lock() getwdCache.dir = dir getwdCache.Unlock() return dir, nil }