build: move package sources from src/pkg to src

Preparation was in CL 134570043.
This CL contains only the effect of 'hg mv src/pkg/* src'.
For more about the move, see golang.org/s/go14nopkg.

83 files changed, 9855 insertions, 0 deletions

diff --git a/src/os/dir_plan9.go b/src/os/dir_plan9.go
new file mode 100644
index 000000000..8195c02a4
--- /dev/null
+++ b/src/os/dir_plan9.go
@@ -0,0 +1,73 @@
+// 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 (
+	"io"
+	"syscall"
+)
+
+func (file *File) readdir(n int) ([]FileInfo, error) {
+	// If this file has no dirinfo, create one.
+	if file.dirinfo == nil {
+		file.dirinfo = new(dirInfo)
+	}
+	d := file.dirinfo
+	size := n
+	if size <= 0 {
+		size = 100
+		n = -1
+	}
+	fi := make([]FileInfo, 0, size) // Empty with room to grow.
+	for n != 0 {
+		// Refill the buffer if necessary.
+		if d.bufp >= d.nbuf {
+			nb, err := file.Read(d.buf[:])
+
+			// Update the buffer state before checking for errors.
+			d.bufp, d.nbuf = 0, nb
+
+			if err != nil {
+				if err == io.EOF {
+					break
+				}
+				return fi, &PathError{"readdir", file.name, err}
+			}
+			if nb < syscall.STATFIXLEN {
+				return fi, &PathError{"readdir", file.name, syscall.ErrShortStat}
+			}
+		}
+
+		// Get a record from the buffer.
+		b := d.buf[d.bufp:]
+		m := int(uint16(b[0])|uint16(b[1])<<8) + 2
+		if m < syscall.STATFIXLEN {
+			return fi, &PathError{"readdir", file.name, syscall.ErrShortStat}
+		}
+
+		dir, err := syscall.UnmarshalDir(b[:m])
+		if err != nil {
+			return fi, &PathError{"readdir", file.name, err}
+		}
+		fi = append(fi, fileInfoFromStat(dir))
+
+		d.bufp += m
+		n--
+	}
+
+	if n >= 0 && len(fi) == 0 {
+		return fi, io.EOF
+	}
+	return fi, nil
+}
+
+func (file *File) readdirnames(n int) (names []string, err error) {
+	fi, err := file.Readdir(n)
+	names = make([]string, len(fi))
+	for i := range fi {
+		names[i] = fi[i].Name()
+	}
+	return
+}
diff --git a/src/os/dir_unix.go b/src/os/dir_unix.go
new file mode 100644
index 000000000..d353e405e
--- /dev/null
+++ b/src/os/dir_unix.go
@@ -0,0 +1,58 @@
+// 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.
+
+// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
+
+package os
+
+import (
+	"io"
+	"syscall"
+)
+
+const (
+	blockSize = 4096
+)
+
+func (f *File) readdirnames(n int) (names []string, err error) {
+	// If this file has no dirinfo, create one.
+	if f.dirinfo == nil {
+		f.dirinfo = new(dirInfo)
+		// The buffer must be at least a block long.
+		f.dirinfo.buf = make([]byte, blockSize)
+	}
+	d := f.dirinfo
+
+	size := n
+	if size <= 0 {
+		size = 100
+		n = -1
+	}
+
+	names = make([]string, 0, size) // Empty with room to grow.
+	for n != 0 {
+		// Refill the buffer if necessary
+		if d.bufp >= d.nbuf {
+			d.bufp = 0
+			var errno error
+			d.nbuf, errno = syscall.ReadDirent(f.fd, d.buf)
+			if errno != nil {
+				return names, NewSyscallError("readdirent", errno)
+			}
+			if d.nbuf <= 0 {
+				break // EOF
+			}
+		}
+
+		// Drain the buffer
+		var nb, nc int
+		nb, nc, names = syscall.ParseDirent(d.buf[d.bufp:d.nbuf], n, names)
+		d.bufp += nb
+		n -= nc
+	}
+	if n >= 0 && len(names) == 0 {
+		return names, io.EOF
+	}
+	return names, nil
+}
diff --git a/src/os/dir_windows.go b/src/os/dir_windows.go
new file mode 100644
index 000000000..931316048
--- /dev/null
+++ b/src/os/dir_windows.go
@@ -0,0 +1,14 @@
+// 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
+
+func (file *File) readdirnames(n int) (names []string, err error) {
+	fis, err := file.Readdir(n)
+	names = make([]string, len(fis))
+	for i, fi := range fis {
+		names[i] = fi.Name()
+	}
+	return names, err
+}
diff --git a/src/os/doc.go b/src/os/doc.go
new file mode 100644
index 000000000..389a8eb14
--- /dev/null
+++ b/src/os/doc.go
@@ -0,0 +1,135 @@
+// Copyright 2012 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 "time"
+
+// FindProcess looks for a running process by its pid.
+// The Process it returns can be used to obtain information
+// about the underlying operating system process.
+func FindProcess(pid int) (p *Process, err error) {
+	return findProcess(pid)
+}
+
+// StartProcess starts a new process with the program, arguments and attributes
+// specified by name, argv and attr.
+//
+// StartProcess is a low-level interface. The os/exec package provides
+// higher-level interfaces.
+//
+// If there is an error, it will be of type *PathError.
+func StartProcess(name string, argv []string, attr *ProcAttr) (*Process, error) {
+	return startProcess(name, argv, attr)
+}
+
+// Release releases any resources associated with the Process p,
+// rendering it unusable in the future.
+// Release only needs to be called if Wait is not.
+func (p *Process) Release() error {
+	return p.release()
+}
+
+// Kill causes the Process to exit immediately.
+func (p *Process) Kill() error {
+	return p.kill()
+}
+
+// Wait waits for the Process to exit, and then returns a
+// ProcessState describing its status and an error, if any.
+// Wait releases any resources associated with the Process.
+// On most operating systems, the Process must be a child
+// of the current process or an error will be returned.
+func (p *Process) Wait() (*ProcessState, error) {
+	return p.wait()
+}
+
+// Signal sends a signal to the Process.
+// Sending Interrupt on Windows is not implemented.
+func (p *Process) Signal(sig Signal) error {
+	return p.signal(sig)
+}
+
+// UserTime returns the user CPU time of the exited process and its children.
+func (p *ProcessState) UserTime() time.Duration {
+	return p.userTime()
+}
+
+// SystemTime returns the system CPU time of the exited process and its children.
+func (p *ProcessState) SystemTime() time.Duration {
+	return p.systemTime()
+}
+
+// Exited reports whether the program has exited.
+func (p *ProcessState) Exited() bool {
+	return p.exited()
+}
+
+// Success reports whether the program exited successfully,
+// such as with exit status 0 on Unix.
+func (p *ProcessState) Success() bool {
+	return p.success()
+}
+
+// Sys returns system-dependent exit information about
+// the process.  Convert it to the appropriate underlying
+// type, such as syscall.WaitStatus on Unix, to access its contents.
+func (p *ProcessState) Sys() interface{} {
+	return p.sys()
+}
+
+// SysUsage returns system-dependent resource usage information about
+// the exited process.  Convert it to the appropriate underlying
+// type, such as *syscall.Rusage on Unix, to access its contents.
+// (On Unix, *syscall.Rusage matches struct rusage as defined in the
+// getrusage(2) manual page.)
+func (p *ProcessState) SysUsage() interface{} {
+	return p.sysUsage()
+}
+
+// Hostname returns the host name reported by the kernel.
+func Hostname() (name string, err error) {
+	return hostname()
+}
+
+// Readdir reads the contents of the directory associated with file and
+// returns a slice of up to n FileInfo values, as would be returned
+// by Lstat, in directory order. Subsequent calls on the same file will yield
+// further FileInfos.
+//
+// If n > 0, Readdir returns at most n FileInfo structures. In this case, if
+// Readdir returns an empty slice, it will return a non-nil error
+// explaining why. At the end of a directory, the error is io.EOF.
+//
+// If n <= 0, Readdir returns all the FileInfo from the directory in
+// a single slice. In this case, if Readdir succeeds (reads all
+// the way to the end of the directory), it returns the slice and a
+// nil error. If it encounters an error before the end of the
+// directory, Readdir returns the FileInfo read until that point
+// and a non-nil error.
+func (f *File) Readdir(n int) (fi []FileInfo, err error) {
+	if f == nil {
+		return nil, ErrInvalid
+	}
+	return f.readdir(n)
+}
+
+// Readdirnames reads and returns a slice of names from the directory f.
+//
+// If n > 0, Readdirnames returns at most n names. In this case, if
+// Readdirnames returns an empty slice, it will return a non-nil error
+// explaining why. At the end of a directory, the error is io.EOF.
+//
+// If n <= 0, Readdirnames returns all the names from the directory in
+// a single slice. In this case, if Readdirnames succeeds (reads all
+// the way to the end of the directory), it returns the slice and a
+// nil error. If it encounters an error before the end of the
+// directory, Readdirnames returns the names read until that point and
+// a non-nil error.
+func (f *File) Readdirnames(n int) (names []string, err error) {
+	if f == nil {
+		return nil, ErrInvalid
+	}
+	return f.readdirnames(n)
+}
diff --git a/src/os/env.go b/src/os/env.go
new file mode 100644
index 000000000..db7fc72b8
--- /dev/null
+++ b/src/os/env.go
@@ -0,0 +1,103 @@
+// Copyright 2010 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.
+
+// General environment variables.
+
+package os
+
+import "syscall"
+
+// Expand replaces ${var} or $var in the string based on the mapping function.
+// For example, os.ExpandEnv(s) is equivalent to os.Expand(s, os.Getenv).
+func Expand(s string, mapping func(string) string) string {
+	buf := make([]byte, 0, 2*len(s))
+	// ${} is all ASCII, so bytes are fine for this operation.
+	i := 0
+	for j := 0; j < len(s); j++ {
+		if s[j] == '$' && j+1 < len(s) {
+			buf = append(buf, s[i:j]...)
+			name, w := getShellName(s[j+1:])
+			buf = append(buf, mapping(name)...)
+			j += w
+			i = j + 1
+		}
+	}
+	return string(buf) + s[i:]
+}
+
+// ExpandEnv replaces ${var} or $var in the string according to the values
+// of the current environment variables.  References to undefined
+// variables are replaced by the empty string.
+func ExpandEnv(s string) string {
+	return Expand(s, Getenv)
+}
+
+// isSpellSpecialVar reports whether the character identifies a special
+// shell variable such as $*.
+func isShellSpecialVar(c uint8) bool {
+	switch c {
+	case '*', '#', '$', '@', '!', '?', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
+		return true
+	}
+	return false
+}
+
+// isAlphaNum reports whether the byte is an ASCII letter, number, or underscore
+func isAlphaNum(c uint8) bool {
+	return c == '_' || '0' <= c && c <= '9' || 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z'
+}
+
+// getName returns the name that begins the string and the number of bytes
+// consumed to extract it.  If the name is enclosed in {}, it's part of a ${}
+// expansion and two more bytes are needed than the length of the name.
+func getShellName(s string) (string, int) {
+	switch {
+	case s[0] == '{':
+		if len(s) > 2 && isShellSpecialVar(s[1]) && s[2] == '}' {
+			return s[1:2], 3
+		}
+		// Scan to closing brace
+		for i := 1; i < len(s); i++ {
+			if s[i] == '}' {
+				return s[1:i], i + 1
+			}
+		}
+		return "", 1 // Bad syntax; just eat the brace.
+	case isShellSpecialVar(s[0]):
+		return s[0:1], 1
+	}
+	// Scan alphanumerics.
+	var i int
+	for i = 0; i < len(s) && isAlphaNum(s[i]); i++ {
+	}
+	return s[:i], i
+}
+
+// Getenv retrieves the value of the environment variable named by the key.
+// It returns the value, which will be empty if the variable is not present.
+func Getenv(key string) string {
+	v, _ := syscall.Getenv(key)
+	return v
+}
+
+// Setenv sets the value of the environment variable named by the key.
+// It returns an error, if any.
+func Setenv(key, value string) error {
+	err := syscall.Setenv(key, value)
+	if err != nil {
+		return NewSyscallError("setenv", err)
+	}
+	return nil
+}
+
+// Clearenv deletes all environment variables.
+func Clearenv() {
+	syscall.Clearenv()
+}
+
+// Environ returns a copy of strings representing the environment,
+// in the form "key=value".
+func Environ() []string {
+	return syscall.Environ()
+}
diff --git a/src/os/env_test.go b/src/os/env_test.go
new file mode 100644
index 000000000..991fa4d05
--- /dev/null
+++ b/src/os/env_test.go
@@ -0,0 +1,70 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os_test
+
+import (
+	. "os"
+	"reflect"
+	"testing"
+)
+
+// testGetenv gives us a controlled set of variables for testing Expand.
+func testGetenv(s string) string {
+	switch s {
+	case "*":
+		return "all the args"
+	case "#":
+		return "NARGS"
+	case "$":
+		return "PID"
+	case "1":
+		return "ARGUMENT1"
+	case "HOME":
+		return "/usr/gopher"
+	case "H":
+		return "(Value of H)"
+	case "home_1":
+		return "/usr/foo"
+	case "_":
+		return "underscore"
+	}
+	return ""
+}
+
+var expandTests = []struct {
+	in, out string
+}{
+	{"", ""},
+	{"$*", "all the args"},
+	{"$$", "PID"},
+	{"${*}", "all the args"},
+	{"$1", "ARGUMENT1"},
+	{"${1}", "ARGUMENT1"},
+	{"now is the time", "now is the time"},
+	{"$HOME", "/usr/gopher"},
+	{"$home_1", "/usr/foo"},
+	{"${HOME}", "/usr/gopher"},
+	{"${H}OME", "(Value of H)OME"},
+	{"A$$$#$1$H$home_1*B", "APIDNARGSARGUMENT1(Value of H)/usr/foo*B"},
+}
+
+func TestExpand(t *testing.T) {
+	for _, test := range expandTests {
+		result := Expand(test.in, testGetenv)
+		if result != test.out {
+			t.Errorf("Expand(%q)=%q; expected %q", test.in, result, test.out)
+		}
+	}
+}
+
+func TestConsistentEnviron(t *testing.T) {
+	e0 := Environ()
+	for i := 0; i < 10; i++ {
+		e1 := Environ()
+		if !reflect.DeepEqual(e0, e1) {
+			t.Fatalf("environment changed")
+		}
+	}
+}
diff --git a/src/os/env_unix_test.go b/src/os/env_unix_test.go
new file mode 100644
index 000000000..5ec07ee1b
--- /dev/null
+++ b/src/os/env_unix_test.go
@@ -0,0 +1,30 @@
+// Copyright 2013 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.
+
+// +build darwin dragonfly freebsd linux netbsd openbsd solaris
+
+package os_test
+
+import (
+	. "os"
+	"testing"
+)
+
+var setenvEinvalTests = []struct {
+	k, v string
+}{
+	{"", ""},      // empty key
+	{"k=v", ""},   // '=' in key
+	{"\x00", ""},  // '\x00' in key
+	{"k", "\x00"}, // '\x00' in value
+}
+
+func TestSetenvUnixEinval(t *testing.T) {
+	for _, tt := range setenvEinvalTests {
+		err := Setenv(tt.k, tt.v)
+		if err == nil {
+			t.Errorf(`Setenv(%q, %q) == nil, want error`, tt.k, tt.v)
+		}
+	}
+}
diff --git a/src/os/error.go b/src/os/error.go
new file mode 100644
index 000000000..8810e6930
--- /dev/null
+++ b/src/os/error.go
@@ -0,0 +1,65 @@
+// 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 (
+	"errors"
+)
+
+// Portable analogs of some common system call errors.
+var (
+	ErrInvalid    = errors.New("invalid argument")
+	ErrPermission = errors.New("permission denied")
+	ErrExist      = errors.New("file already exists")
+	ErrNotExist   = errors.New("file does not exist")
+)
+
+// PathError records an error and the operation and file path that caused it.
+type PathError struct {
+	Op   string
+	Path string
+	Err  error
+}
+
+func (e *PathError) Error() string { return e.Op + " " + e.Path + ": " + e.Err.Error() }
+
+// SyscallError records an error from a specific system call.
+type SyscallError struct {
+	Syscall string
+	Err     error
+}
+
+func (e *SyscallError) Error() string { return e.Syscall + ": " + e.Err.Error() }
+
+// NewSyscallError returns, as an error, a new SyscallError
+// with the given system call name and error details.
+// As a convenience, if err is nil, NewSyscallError returns nil.
+func NewSyscallError(syscall string, err error) error {
+	if err == nil {
+		return nil
+	}
+	return &SyscallError{syscall, err}
+}
+
+// IsExist returns a boolean indicating whether the error is known to report
+// that a file or directory already exists. It is satisfied by ErrExist as
+// well as some syscall errors.
+func IsExist(err error) bool {
+	return isExist(err)
+}
+
+// IsNotExist returns a boolean indicating whether the error is known to
+// report that a file or directory does not exist. It is satisfied by
+// ErrNotExist as well as some syscall errors.
+func IsNotExist(err error) bool {
+	return isNotExist(err)
+}
+
+// IsPermission returns a boolean indicating whether the error is known to
+// report that permission is denied. It is satisfied by ErrPermission as well
+// as some syscall errors.
+func IsPermission(err error) bool {
+	return isPermission(err)
+}
diff --git a/src/os/error_plan9.go b/src/os/error_plan9.go
new file mode 100644
index 000000000..62d4e420e
--- /dev/null
+++ b/src/os/error_plan9.go
@@ -0,0 +1,53 @@
+// Copyright 2011 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
+
+func isExist(err error) bool {
+	switch pe := err.(type) {
+	case nil:
+		return false
+	case *PathError:
+		err = pe.Err
+	case *LinkError:
+		err = pe.Err
+	}
+	return contains(err.Error(), " exists")
+}
+
+func isNotExist(err error) bool {
+	switch pe := err.(type) {
+	case nil:
+		return false
+	case *PathError:
+		err = pe.Err
+	case *LinkError:
+		err = pe.Err
+	}
+	return contains(err.Error(), "does not exist") || contains(err.Error(), "not found")
+}
+
+func isPermission(err error) bool {
+	switch pe := err.(type) {
+	case nil:
+		return false
+	case *PathError:
+		err = pe.Err
+	case *LinkError:
+		err = pe.Err
+	}
+	return contains(err.Error(), "permission denied")
+}
+
+// contains is a local version of strings.Contains. It knows len(sep) > 1.
+func contains(s, sep string) bool {
+	n := len(sep)
+	c := sep[0]
+	for i := 0; i+n <= len(s); i++ {
+		if s[i] == c && s[i:i+n] == sep {
+			return true
+		}
+	}
+	return false
+}
diff --git a/src/os/error_test.go b/src/os/error_test.go
new file mode 100644
index 000000000..02ed2351c
--- /dev/null
+++ b/src/os/error_test.go
@@ -0,0 +1,132 @@
+// Copyright 2012 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_test
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestErrIsExist(t *testing.T) {
+	f, err := ioutil.TempFile("", "_Go_ErrIsExist")
+	if err != nil {
+		t.Fatalf("open ErrIsExist tempfile: %s", err)
+		return
+	}
+	defer os.Remove(f.Name())
+	defer f.Close()
+	f2, err := os.OpenFile(f.Name(), os.O_RDWR|os.O_CREATE|os.O_EXCL, 0600)
+	if err == nil {
+		f2.Close()
+		t.Fatal("Open should have failed")
+		return
+	}
+	if s := checkErrorPredicate("os.IsExist", os.IsExist, err); s != "" {
+		t.Fatal(s)
+		return
+	}
+}
+
+func testErrNotExist(name string) string {
+	f, err := os.Open(name)
+	if err == nil {
+		f.Close()
+		return "Open should have failed"
+	}
+	if s := checkErrorPredicate("os.IsNotExist", os.IsNotExist, err); s != "" {
+		return s
+	}
+
+	err = os.Chdir(name)
+	if err == nil {
+		return "Chdir should have failed"
+	}
+	if s := checkErrorPredicate("os.IsNotExist", os.IsNotExist, err); s != "" {
+		return s
+	}
+	return ""
+}
+
+func TestErrIsNotExist(t *testing.T) {
+	tmpDir, err := ioutil.TempDir("", "_Go_ErrIsNotExist")
+	if err != nil {
+		t.Fatalf("create ErrIsNotExist tempdir: %s", err)
+		return
+	}
+	defer os.RemoveAll(tmpDir)
+
+	name := filepath.Join(tmpDir, "NotExists")
+	if s := testErrNotExist(name); s != "" {
+		t.Fatal(s)
+		return
+	}
+
+	name = filepath.Join(name, "NotExists2")
+	if s := testErrNotExist(name); s != "" {
+		t.Fatal(s)
+		return
+	}
+}
+
+func checkErrorPredicate(predName string, pred func(error) bool, err error) string {
+	if !pred(err) {
+		return fmt.Sprintf("%s does not work as expected for %#v", predName, err)
+	}
+	return ""
+}
+
+var isExistTests = []struct {
+	err   error
+	is    bool
+	isnot bool
+}{
+	{&os.PathError{Err: os.ErrInvalid}, false, false},
+	{&os.PathError{Err: os.ErrPermission}, false, false},
+	{&os.PathError{Err: os.ErrExist}, true, false},
+	{&os.PathError{Err: os.ErrNotExist}, false, true},
+	{&os.LinkError{Err: os.ErrInvalid}, false, false},
+	{&os.LinkError{Err: os.ErrPermission}, false, false},
+	{&os.LinkError{Err: os.ErrExist}, true, false},
+	{&os.LinkError{Err: os.ErrNotExist}, false, true},
+	{nil, false, false},
+}
+
+func TestIsExist(t *testing.T) {
+	for _, tt := range isExistTests {
+		if is := os.IsExist(tt.err); is != tt.is {
+			t.Errorf("os.IsExist(%T %v) = %v, want %v", tt.err, tt.err, is, tt.is)
+		}
+		if isnot := os.IsNotExist(tt.err); isnot != tt.isnot {
+			t.Errorf("os.IsNotExist(%T %v) = %v, want %v", tt.err, tt.err, isnot, tt.isnot)
+		}
+	}
+}
+
+func TestErrPathNUL(t *testing.T) {
+	f, err := ioutil.TempFile("", "_Go_ErrPathNUL\x00")
+	if err == nil {
+		f.Close()
+		t.Fatal("TempFile should have failed")
+	}
+	f, err = ioutil.TempFile("", "_Go_ErrPathNUL")
+	if err != nil {
+		t.Fatalf("open ErrPathNUL tempfile: %s", err)
+	}
+	defer os.Remove(f.Name())
+	defer f.Close()
+	f2, err := os.OpenFile(f.Name(), os.O_RDWR, 0600)
+	if err != nil {
+		t.Fatalf("open ErrPathNUL: %s", err)
+	}
+	f2.Close()
+	f2, err = os.OpenFile(f.Name()+"\x00", os.O_RDWR, 0600)
+	if err == nil {
+		f2.Close()
+		t.Fatal("Open should have failed")
+	}
+}
diff --git a/src/os/error_unix.go b/src/os/error_unix.go
new file mode 100644
index 000000000..f2aabbb45
--- /dev/null
+++ b/src/os/error_unix.go
@@ -0,0 +1,45 @@
+// 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.
+
+// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
+
+package os
+
+import "syscall"
+
+func isExist(err error) bool {
+	switch pe := err.(type) {
+	case nil:
+		return false
+	case *PathError:
+		err = pe.Err
+	case *LinkError:
+		err = pe.Err
+	}
+	return err == syscall.EEXIST || err == ErrExist
+}
+
+func isNotExist(err error) bool {
+	switch pe := err.(type) {
+	case nil:
+		return false
+	case *PathError:
+		err = pe.Err
+	case *LinkError:
+		err = pe.Err
+	}
+	return err == syscall.ENOENT || err == ErrNotExist
+}
+
+func isPermission(err error) bool {
+	switch pe := err.(type) {
+	case nil:
+		return false
+	case *PathError:
+		err = pe.Err
+	case *LinkError:
+		err = pe.Err
+	}
+	return err == syscall.EACCES || err == syscall.EPERM || err == ErrPermission
+}
diff --git a/src/os/error_windows.go b/src/os/error_windows.go
new file mode 100644
index 000000000..83db6c078
--- /dev/null
+++ b/src/os/error_windows.go
@@ -0,0 +1,45 @@
+// Copyright 2012 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 "syscall"
+
+func isExist(err error) bool {
+	switch pe := err.(type) {
+	case nil:
+		return false
+	case *PathError:
+		err = pe.Err
+	case *LinkError:
+		err = pe.Err
+	}
+	return err == syscall.ERROR_ALREADY_EXISTS ||
+		err == syscall.ERROR_FILE_EXISTS || err == ErrExist
+}
+
+func isNotExist(err error) bool {
+	switch pe := err.(type) {
+	case nil:
+		return false
+	case *PathError:
+		err = pe.Err
+	case *LinkError:
+		err = pe.Err
+	}
+	return err == syscall.ERROR_FILE_NOT_FOUND ||
+		err == syscall.ERROR_PATH_NOT_FOUND || err == ErrNotExist
+}
+
+func isPermission(err error) bool {
+	switch pe := err.(type) {
+	case nil:
+		return false
+	case *PathError:
+		err = pe.Err
+	case *LinkError:
+		err = pe.Err
+	}
+	return err == syscall.ERROR_ACCESS_DENIED || err == ErrPermission
+}
diff --git a/src/os/error_windows_test.go b/src/os/error_windows_test.go
new file mode 100644
index 000000000..3e6504f8d
--- /dev/null
+++ b/src/os/error_windows_test.go
@@ -0,0 +1,47 @@
+// Copyright 2012 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_test
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestErrIsExistAfterRename(t *testing.T) {
+	dir, err := ioutil.TempDir("", "go-build")
+	if err != nil {
+		t.Fatalf("Create temp directory: %v", err)
+	}
+	defer os.RemoveAll(dir)
+
+	src := filepath.Join(dir, "src")
+	dest := filepath.Join(dir, "dest")
+
+	f, err := os.Create(src)
+	if err != nil {
+		t.Fatalf("Create file %v: %v", src, err)
+	}
+	f.Close()
+	err = os.Rename(src, dest)
+	if err != nil {
+		t.Fatalf("Rename %v to %v: %v", src, dest, err)
+	}
+
+	f, err = os.Create(src)
+	if err != nil {
+		t.Fatalf("Create file %v: %v", src, err)
+	}
+	f.Close()
+	err = os.Rename(src, dest)
+	if err == nil {
+		t.Fatal("Rename should have failed")
+	}
+	if s := checkErrorPredicate("os.IsExist", os.IsExist, err); s != "" {
+		t.Fatal(s)
+		return
+	}
+}
diff --git a/src/os/exec.go b/src/os/exec.go
new file mode 100644
index 000000000..5aea3098b
--- /dev/null
+++ b/src/os/exec.go
@@ -0,0 +1,70 @@
+// 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/atomic"
+	"syscall"
+)
+
+// Process stores the information about a process created by StartProcess.
+type Process struct {
+	Pid    int
+	handle uintptr
+	isdone uint32 // process has been successfully waited on, non zero if true
+}
+
+func newProcess(pid int, handle uintptr) *Process {
+	p := &Process{Pid: pid, handle: handle}
+	runtime.SetFinalizer(p, (*Process).Release)
+	return p
+}
+
+func (p *Process) setDone() {
+	atomic.StoreUint32(&p.isdone, 1)
+}
+
+func (p *Process) done() bool {
+	return atomic.LoadUint32(&p.isdone) > 0
+}
+
+// ProcAttr holds the attributes that will be applied to a new process
+// started by StartProcess.
+type ProcAttr struct {
+	// If Dir is non-empty, the child changes into the directory before
+	// creating the process.
+	Dir string
+	// If Env is non-nil, it gives the environment variables for the
+	// new process in the form returned by Environ.
+	// If it is nil, the result of Environ will be used.
+	Env []string
+	// Files specifies the open files inherited by the new process.  The
+	// first three entries correspond to standard input, standard output, and
+	// standard error.  An implementation may support additional entries,
+	// depending on the underlying operating system.  A nil entry corresponds
+	// to that file being closed when the process starts.
+	Files []*File
+
+	// Operating system-specific process creation attributes.
+	// Note that setting this field means that your program
+	// may not execute properly or even compile on some
+	// operating systems.
+	Sys *syscall.SysProcAttr
+}
+
+// A Signal represents an operating system signal.
+// The usual underlying implementation is operating system-dependent:
+// on Unix it is syscall.Signal.
+type Signal interface {
+	String() string
+	Signal() // to distinguish from other Stringers
+}
+
+// Getpid returns the process id of the caller.
+func Getpid() int { return syscall.Getpid() }
+
+// Getppid returns the process id of the caller's parent.
+func Getppid() int { return syscall.Getppid() }
diff --git a/src/os/exec/example_test.go b/src/os/exec/example_test.go
new file mode 100644
index 000000000..55eaac8ab
--- /dev/null
+++ b/src/os/exec/example_test.go
@@ -0,0 +1,75 @@
+// Copyright 2012 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 exec_test
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"log"
+	"os/exec"
+	"strings"
+)
+
+func ExampleLookPath() {
+	path, err := exec.LookPath("fortune")
+	if err != nil {
+		log.Fatal("installing fortune is in your future")
+	}
+	fmt.Printf("fortune is available at %s\n", path)
+}
+
+func ExampleCommand() {
+	cmd := exec.Command("tr", "a-z", "A-Z")
+	cmd.Stdin = strings.NewReader("some input")
+	var out bytes.Buffer
+	cmd.Stdout = &out
+	err := cmd.Run()
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("in all caps: %q\n", out.String())
+}
+
+func ExampleCmd_Output() {
+	out, err := exec.Command("date").Output()
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("The date is %s\n", out)
+}
+
+func ExampleCmd_Start() {
+	cmd := exec.Command("sleep", "5")
+	err := cmd.Start()
+	if err != nil {
+		log.Fatal(err)
+	}
+	log.Printf("Waiting for command to finish...")
+	err = cmd.Wait()
+	log.Printf("Command finished with error: %v", err)
+}
+
+func ExampleCmd_StdoutPipe() {
+	cmd := exec.Command("echo", "-n", `{"Name": "Bob", "Age": 32}`)
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		log.Fatal(err)
+	}
+	if err := cmd.Start(); err != nil {
+		log.Fatal(err)
+	}
+	var person struct {
+		Name string
+		Age  int
+	}
+	if err := json.NewDecoder(stdout).Decode(&person); err != nil {
+		log.Fatal(err)
+	}
+	if err := cmd.Wait(); err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("%s is %d years old\n", person.Name, person.Age)
+}
diff --git a/src/os/exec/exec.go b/src/os/exec/exec.go
new file mode 100644
index 000000000..4aded4171
--- /dev/null
+++ b/src/os/exec/exec.go
@@ -0,0 +1,493 @@
+// 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 exec runs external commands. It wraps os.StartProcess to make it
+// easier to remap stdin and stdout, connect I/O with pipes, and do other
+// adjustments.
+package exec
+
+import (
+	"bytes"
+	"errors"
+	"io"
+	"os"
+	"path/filepath"
+	"runtime"
+	"strconv"
+	"strings"
+	"sync"
+	"syscall"
+)
+
+// Error records the name of a binary that failed to be executed
+// and the reason it failed.
+type Error struct {
+	Name string
+	Err  error
+}
+
+func (e *Error) Error() string {
+	return "exec: " + strconv.Quote(e.Name) + ": " + e.Err.Error()
+}
+
+// Cmd represents an external command being prepared or run.
+type Cmd struct {
+	// Path is the path of the command to run.
+	//
+	// This is the only field that must be set to a non-zero
+	// value. If Path is relative, it is evaluated relative
+	// to Dir.
+	Path string
+
+	// Args holds command line arguments, including the command as Args[0].
+	// If the Args field is empty or nil, Run uses {Path}.
+	//
+	// In typical use, both Path and Args are set by calling Command.
+	Args []string
+
+	// Env specifies the environment of the process.
+	// If Env is nil, Run uses the current process's environment.
+	Env []string
+
+	// Dir specifies the working directory of the command.
+	// If Dir is the empty string, Run runs the command in the
+	// calling process's current directory.
+	Dir string
+
+	// Stdin specifies the process's standard input. If Stdin is
+	// nil, the process reads from the null device (os.DevNull).
+	Stdin io.Reader
+
+	// Stdout and Stderr specify the process's standard output and error.
+	//
+	// If either is nil, Run connects the corresponding file descriptor
+	// to the null device (os.DevNull).
+	//
+	// If Stdout and Stderr are the same writer, at most one
+	// goroutine at a time will call Write.
+	Stdout io.Writer
+	Stderr io.Writer
+
+	// ExtraFiles specifies additional open files to be inherited by the
+	// new process. It does not include standard input, standard output, or
+	// standard error. If non-nil, entry i becomes file descriptor 3+i.
+	//
+	// BUG: on OS X 10.6, child processes may sometimes inherit unwanted fds.
+	// http://golang.org/issue/2603
+	ExtraFiles []*os.File
+
+	// SysProcAttr holds optional, operating system-specific attributes.
+	// Run passes it to os.StartProcess as the os.ProcAttr's Sys field.
+	SysProcAttr *syscall.SysProcAttr
+
+	// Process is the underlying process, once started.
+	Process *os.Process
+
+	// ProcessState contains information about an exited process,
+	// available after a call to Wait or Run.
+	ProcessState *os.ProcessState
+
+	lookPathErr     error // LookPath error, if any.
+	finished        bool  // when Wait was called
+	childFiles      []*os.File
+	closeAfterStart []io.Closer
+	closeAfterWait  []io.Closer
+	goroutine       []func() error
+	errch           chan error // one send per goroutine
+}
+
+// Command returns the Cmd struct to execute the named program with
+// the given arguments.
+//
+// It sets only the Path and Args in the returned structure.
+//
+// If name contains no path separators, Command uses LookPath to
+// resolve the path to a complete name if possible. Otherwise it uses
+// name directly.
+//
+// The returned Cmd's Args field is constructed from the command name
+// followed by the elements of arg, so arg should not include the
+// command name itself. For example, Command("echo", "hello")
+func Command(name string, arg ...string) *Cmd {
+	cmd := &Cmd{
+		Path: name,
+		Args: append([]string{name}, arg...),
+	}
+	if filepath.Base(name) == name {
+		if lp, err := LookPath(name); err != nil {
+			cmd.lookPathErr = err
+		} else {
+			cmd.Path = lp
+		}
+	}
+	return cmd
+}
+
+// interfaceEqual protects against panics from doing equality tests on
+// two interfaces with non-comparable underlying types.
+func interfaceEqual(a, b interface{}) bool {
+	defer func() {
+		recover()
+	}()
+	return a == b
+}
+
+func (c *Cmd) envv() []string {
+	if c.Env != nil {
+		return c.Env
+	}
+	return os.Environ()
+}
+
+func (c *Cmd) argv() []string {
+	if len(c.Args) > 0 {
+		return c.Args
+	}
+	return []string{c.Path}
+}
+
+func (c *Cmd) stdin() (f *os.File, err error) {
+	if c.Stdin == nil {
+		f, err = os.Open(os.DevNull)
+		if err != nil {
+			return
+		}
+		c.closeAfterStart = append(c.closeAfterStart, f)
+		return
+	}
+
+	if f, ok := c.Stdin.(*os.File); ok {
+		return f, nil
+	}
+
+	pr, pw, err := os.Pipe()
+	if err != nil {
+		return
+	}
+
+	c.closeAfterStart = append(c.closeAfterStart, pr)
+	c.closeAfterWait = append(c.closeAfterWait, pw)
+	c.goroutine = append(c.goroutine, func() error {
+		_, err := io.Copy(pw, c.Stdin)
+		if err1 := pw.Close(); err == nil {
+			err = err1
+		}
+		return err
+	})
+	return pr, nil
+}
+
+func (c *Cmd) stdout() (f *os.File, err error) {
+	return c.writerDescriptor(c.Stdout)
+}
+
+func (c *Cmd) stderr() (f *os.File, err error) {
+	if c.Stderr != nil && interfaceEqual(c.Stderr, c.Stdout) {
+		return c.childFiles[1], nil
+	}
+	return c.writerDescriptor(c.Stderr)
+}
+
+func (c *Cmd) writerDescriptor(w io.Writer) (f *os.File, err error) {
+	if w == nil {
+		f, err = os.OpenFile(os.DevNull, os.O_WRONLY, 0)
+		if err != nil {
+			return
+		}
+		c.closeAfterStart = append(c.closeAfterStart, f)
+		return
+	}
+
+	if f, ok := w.(*os.File); ok {
+		return f, nil
+	}
+
+	pr, pw, err := os.Pipe()
+	if err != nil {
+		return
+	}
+
+	c.closeAfterStart = append(c.closeAfterStart, pw)
+	c.closeAfterWait = append(c.closeAfterWait, pr)
+	c.goroutine = append(c.goroutine, func() error {
+		_, err := io.Copy(w, pr)
+		return err
+	})
+	return pw, nil
+}
+
+func (c *Cmd) closeDescriptors(closers []io.Closer) {
+	for _, fd := range closers {
+		fd.Close()
+	}
+}
+
+// Run starts the specified command and waits for it to complete.
+//
+// The returned error is nil if the command runs, has no problems
+// copying stdin, stdout, and stderr, and exits with a zero exit
+// status.
+//
+// If the command fails to run or doesn't complete successfully, the
+// error is of type *ExitError. Other error types may be
+// returned for I/O problems.
+func (c *Cmd) Run() error {
+	if err := c.Start(); err != nil {
+		return err
+	}
+	return c.Wait()
+}
+
+// lookExtensions finds windows executable by its dir and path.
+// It uses LookPath to try appropriate extensions.
+// lookExtensions does not search PATH, instead it converts `prog` into `.\prog`.
+func lookExtensions(path, dir string) (string, error) {
+	if filepath.Base(path) == path {
+		path = filepath.Join(".", path)
+	}
+	if dir == "" {
+		return LookPath(path)
+	}
+	if filepath.VolumeName(path) != "" {
+		return LookPath(path)
+	}
+	if len(path) > 1 && os.IsPathSeparator(path[0]) {
+		return LookPath(path)
+	}
+	dirandpath := filepath.Join(dir, path)
+	// We assume that LookPath will only add file extension.
+	lp, err := LookPath(dirandpath)
+	if err != nil {
+		return "", err
+	}
+	ext := strings.TrimPrefix(lp, dirandpath)
+	return path + ext, nil
+}
+
+// Start starts the specified command but does not wait for it to complete.
+//
+// The Wait method will return the exit code and release associated resources
+// once the command exits.
+func (c *Cmd) Start() error {
+	if c.lookPathErr != nil {
+		c.closeDescriptors(c.closeAfterStart)
+		c.closeDescriptors(c.closeAfterWait)
+		return c.lookPathErr
+	}
+	if runtime.GOOS == "windows" {
+		lp, err := lookExtensions(c.Path, c.Dir)
+		if err != nil {
+			c.closeDescriptors(c.closeAfterStart)
+			c.closeDescriptors(c.closeAfterWait)
+			return err
+		}
+		c.Path = lp
+	}
+	if c.Process != nil {
+		return errors.New("exec: already started")
+	}
+
+	type F func(*Cmd) (*os.File, error)
+	for _, setupFd := range []F{(*Cmd).stdin, (*Cmd).stdout, (*Cmd).stderr} {
+		fd, err := setupFd(c)
+		if err != nil {
+			c.closeDescriptors(c.closeAfterStart)
+			c.closeDescriptors(c.closeAfterWait)
+			return err
+		}
+		c.childFiles = append(c.childFiles, fd)
+	}
+	c.childFiles = append(c.childFiles, c.ExtraFiles...)
+
+	var err error
+	c.Process, err = os.StartProcess(c.Path, c.argv(), &os.ProcAttr{
+		Dir:   c.Dir,
+		Files: c.childFiles,
+		Env:   c.envv(),
+		Sys:   c.SysProcAttr,
+	})
+	if err != nil {
+		c.closeDescriptors(c.closeAfterStart)
+		c.closeDescriptors(c.closeAfterWait)
+		return err
+	}
+
+	c.closeDescriptors(c.closeAfterStart)
+
+	c.errch = make(chan error, len(c.goroutine))
+	for _, fn := range c.goroutine {
+		go func(fn func() error) {
+			c.errch <- fn()
+		}(fn)
+	}
+
+	return nil
+}
+
+// An ExitError reports an unsuccessful exit by a command.
+type ExitError struct {
+	*os.ProcessState
+}
+
+func (e *ExitError) Error() string {
+	return e.ProcessState.String()
+}
+
+// Wait waits for the command to exit.
+// It must have been started by Start.
+//
+// The returned error is nil if the command runs, has no problems
+// copying stdin, stdout, and stderr, and exits with a zero exit
+// status.
+//
+// If the command fails to run or doesn't complete successfully, the
+// error is of type *ExitError. Other error types may be
+// returned for I/O problems.
+//
+// Wait releases any resources associated with the Cmd.
+func (c *Cmd) Wait() error {
+	if c.Process == nil {
+		return errors.New("exec: not started")
+	}
+	if c.finished {
+		return errors.New("exec: Wait was already called")
+	}
+	c.finished = true
+	state, err := c.Process.Wait()
+	c.ProcessState = state
+
+	var copyError error
+	for range c.goroutine {
+		if err := <-c.errch; err != nil && copyError == nil {
+			copyError = err
+		}
+	}
+
+	c.closeDescriptors(c.closeAfterWait)
+
+	if err != nil {
+		return err
+	} else if !state.Success() {
+		return &ExitError{state}
+	}
+
+	return copyError
+}
+
+// Output runs the command and returns its standard output.
+func (c *Cmd) Output() ([]byte, error) {
+	if c.Stdout != nil {
+		return nil, errors.New("exec: Stdout already set")
+	}
+	var b bytes.Buffer
+	c.Stdout = &b
+	err := c.Run()
+	return b.Bytes(), err
+}
+
+// CombinedOutput runs the command and returns its combined standard
+// output and standard error.
+func (c *Cmd) CombinedOutput() ([]byte, error) {
+	if c.Stdout != nil {
+		return nil, errors.New("exec: Stdout already set")
+	}
+	if c.Stderr != nil {
+		return nil, errors.New("exec: Stderr already set")
+	}
+	var b bytes.Buffer
+	c.Stdout = &b
+	c.Stderr = &b
+	err := c.Run()
+	return b.Bytes(), err
+}
+
+// StdinPipe returns a pipe that will be connected to the command's
+// standard input when the command starts.
+// The pipe will be closed automatically after Wait sees the command exit.
+// A caller need only call Close to force the pipe to close sooner.
+// For example, if the command being run will not exit until standard input
+// is closed, the caller must close the pipe.
+func (c *Cmd) StdinPipe() (io.WriteCloser, error) {
+	if c.Stdin != nil {
+		return nil, errors.New("exec: Stdin already set")
+	}
+	if c.Process != nil {
+		return nil, errors.New("exec: StdinPipe after process started")
+	}
+	pr, pw, err := os.Pipe()
+	if err != nil {
+		return nil, err
+	}
+	c.Stdin = pr
+	c.closeAfterStart = append(c.closeAfterStart, pr)
+	wc := &closeOnce{File: pw}
+	c.closeAfterWait = append(c.closeAfterWait, wc)
+	return wc, nil
+}
+
+type closeOnce struct {
+	*os.File
+
+	once sync.Once
+	err  error
+}
+
+func (c *closeOnce) Close() error {
+	c.once.Do(c.close)
+	return c.err
+}
+
+func (c *closeOnce) close() {
+	c.err = c.File.Close()
+}
+
+// StdoutPipe returns a pipe that will be connected to the command's
+// standard output when the command starts.
+//
+// Wait will close the pipe after seeing the command exit, so most callers
+// need not close the pipe themselves; however, an implication is that
+// it is incorrect to call Wait before all reads from the pipe have completed.
+// For the same reason, it is incorrect to call Run when using StdoutPipe.
+// See the example for idiomatic usage.
+func (c *Cmd) StdoutPipe() (io.ReadCloser, error) {
+	if c.Stdout != nil {
+		return nil, errors.New("exec: Stdout already set")
+	}
+	if c.Process != nil {
+		return nil, errors.New("exec: StdoutPipe after process started")
+	}
+	pr, pw, err := os.Pipe()
+	if err != nil {
+		return nil, err
+	}
+	c.Stdout = pw
+	c.closeAfterStart = append(c.closeAfterStart, pw)
+	c.closeAfterWait = append(c.closeAfterWait, pr)
+	return pr, nil
+}
+
+// StderrPipe returns a pipe that will be connected to the command's
+// standard error when the command starts.
+//
+// Wait will close the pipe after seeing the command exit, so most callers
+// need not close the pipe themselves; however, an implication is that
+// it is incorrect to call Wait before all reads from the pipe have completed.
+// For the same reason, it is incorrect to use Run when using StderrPipe.
+// See the StdoutPipe example for idiomatic usage.
+func (c *Cmd) StderrPipe() (io.ReadCloser, error) {
+	if c.Stderr != nil {
+		return nil, errors.New("exec: Stderr already set")
+	}
+	if c.Process != nil {
+		return nil, errors.New("exec: StderrPipe after process started")
+	}
+	pr, pw, err := os.Pipe()
+	if err != nil {
+		return nil, err
+	}
+	c.Stderr = pw
+	c.closeAfterStart = append(c.closeAfterStart, pw)
+	c.closeAfterWait = append(c.closeAfterWait, pr)
+	return pr, nil
+}
diff --git a/src/os/exec/exec_test.go b/src/os/exec/exec_test.go
new file mode 100644
index 000000000..6f77ac38a
--- /dev/null
+++ b/src/os/exec/exec_test.go
@@ -0,0 +1,726 @@
+// 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.
+
+// Use an external test to avoid os/exec -> net/http -> crypto/x509 -> os/exec
+// circular dependency on non-cgo darwin.
+
+package exec_test
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"log"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strconv"
+	"strings"
+	"testing"
+	"time"
+)
+
+func helperCommand(t *testing.T, s ...string) *exec.Cmd {
+	if runtime.GOOS == "nacl" {
+		t.Skip("skipping on nacl")
+	}
+	cs := []string{"-test.run=TestHelperProcess", "--"}
+	cs = append(cs, s...)
+	cmd := exec.Command(os.Args[0], cs...)
+	cmd.Env = []string{"GO_WANT_HELPER_PROCESS=1"}
+	return cmd
+}
+
+func TestEcho(t *testing.T) {
+	bs, err := helperCommand(t, "echo", "foo bar", "baz").Output()
+	if err != nil {
+		t.Errorf("echo: %v", err)
+	}
+	if g, e := string(bs), "foo bar baz\n"; g != e {
+		t.Errorf("echo: want %q, got %q", e, g)
+	}
+}
+
+func TestCommandRelativeName(t *testing.T) {
+	// Run our own binary as a relative path
+	// (e.g. "_test/exec.test") our parent directory.
+	base := filepath.Base(os.Args[0]) // "exec.test"
+	dir := filepath.Dir(os.Args[0])   // "/tmp/go-buildNNNN/os/exec/_test"
+	if dir == "." {
+		t.Skip("skipping; running test at root somehow")
+	}
+	parentDir := filepath.Dir(dir) // "/tmp/go-buildNNNN/os/exec"
+	dirBase := filepath.Base(dir)  // "_test"
+	if dirBase == "." {
+		t.Skipf("skipping; unexpected shallow dir of %q", dir)
+	}
+
+	cmd := exec.Command(filepath.Join(dirBase, base), "-test.run=TestHelperProcess", "--", "echo", "foo")
+	cmd.Dir = parentDir
+	cmd.Env = []string{"GO_WANT_HELPER_PROCESS=1"}
+
+	out, err := cmd.Output()
+	if err != nil {
+		t.Errorf("echo: %v", err)
+	}
+	if g, e := string(out), "foo\n"; g != e {
+		t.Errorf("echo: want %q, got %q", e, g)
+	}
+}
+
+func TestCatStdin(t *testing.T) {
+	// Cat, testing stdin and stdout.
+	input := "Input string\nLine 2"
+	p := helperCommand(t, "cat")
+	p.Stdin = strings.NewReader(input)
+	bs, err := p.Output()
+	if err != nil {
+		t.Errorf("cat: %v", err)
+	}
+	s := string(bs)
+	if s != input {
+		t.Errorf("cat: want %q, got %q", input, s)
+	}
+}
+
+func TestCatGoodAndBadFile(t *testing.T) {
+	// Testing combined output and error values.
+	bs, err := helperCommand(t, "cat", "/bogus/file.foo", "exec_test.go").CombinedOutput()
+	if _, ok := err.(*exec.ExitError); !ok {
+		t.Errorf("expected *exec.ExitError from cat combined; got %T: %v", err, err)
+	}
+	s := string(bs)
+	sp := strings.SplitN(s, "\n", 2)
+	if len(sp) != 2 {
+		t.Fatalf("expected two lines from cat; got %q", s)
+	}
+	errLine, body := sp[0], sp[1]
+	if !strings.HasPrefix(errLine, "Error: open /bogus/file.foo") {
+		t.Errorf("expected stderr to complain about file; got %q", errLine)
+	}
+	if !strings.Contains(body, "func TestHelperProcess(t *testing.T)") {
+		t.Errorf("expected test code; got %q (len %d)", body, len(body))
+	}
+}
+
+func TestNoExistBinary(t *testing.T) {
+	// Can't run a non-existent binary
+	err := exec.Command("/no-exist-binary").Run()
+	if err == nil {
+		t.Error("expected error from /no-exist-binary")
+	}
+}
+
+func TestExitStatus(t *testing.T) {
+	// Test that exit values are returned correctly
+	cmd := helperCommand(t, "exit", "42")
+	err := cmd.Run()
+	want := "exit status 42"
+	switch runtime.GOOS {
+	case "plan9":
+		want = fmt.Sprintf("exit status: '%s %d: 42'", filepath.Base(cmd.Path), cmd.ProcessState.Pid())
+	}
+	if werr, ok := err.(*exec.ExitError); ok {
+		if s := werr.Error(); s != want {
+			t.Errorf("from exit 42 got exit %q, want %q", s, want)
+		}
+	} else {
+		t.Fatalf("expected *exec.ExitError from exit 42; got %T: %v", err, err)
+	}
+}
+
+func TestPipes(t *testing.T) {
+	check := func(what string, err error) {
+		if err != nil {
+			t.Fatalf("%s: %v", what, err)
+		}
+	}
+	// Cat, testing stdin and stdout.
+	c := helperCommand(t, "pipetest")
+	stdin, err := c.StdinPipe()
+	check("StdinPipe", err)
+	stdout, err := c.StdoutPipe()
+	check("StdoutPipe", err)
+	stderr, err := c.StderrPipe()
+	check("StderrPipe", err)
+
+	outbr := bufio.NewReader(stdout)
+	errbr := bufio.NewReader(stderr)
+	line := func(what string, br *bufio.Reader) string {
+		line, _, err := br.ReadLine()
+		if err != nil {
+			t.Fatalf("%s: %v", what, err)
+		}
+		return string(line)
+	}
+
+	err = c.Start()
+	check("Start", err)
+
+	_, err = stdin.Write([]byte("O:I am output\n"))
+	check("first stdin Write", err)
+	if g, e := line("first output line", outbr), "O:I am output"; g != e {
+		t.Errorf("got %q, want %q", g, e)
+	}
+
+	_, err = stdin.Write([]byte("E:I am error\n"))
+	check("second stdin Write", err)
+	if g, e := line("first error line", errbr), "E:I am error"; g != e {
+		t.Errorf("got %q, want %q", g, e)
+	}
+
+	_, err = stdin.Write([]byte("O:I am output2\n"))
+	check("third stdin Write 3", err)
+	if g, e := line("second output line", outbr), "O:I am output2"; g != e {
+		t.Errorf("got %q, want %q", g, e)
+	}
+
+	stdin.Close()
+	err = c.Wait()
+	check("Wait", err)
+}
+
+const stdinCloseTestString = "Some test string."
+
+// Issue 6270.
+func TestStdinClose(t *testing.T) {
+	check := func(what string, err error) {
+		if err != nil {
+			t.Fatalf("%s: %v", what, err)
+		}
+	}
+	cmd := helperCommand(t, "stdinClose")
+	stdin, err := cmd.StdinPipe()
+	check("StdinPipe", err)
+	// Check that we can access methods of the underlying os.File.`
+	if _, ok := stdin.(interface {
+		Fd() uintptr
+	}); !ok {
+		t.Error("can't access methods of underlying *os.File")
+	}
+	check("Start", cmd.Start())
+	go func() {
+		_, err := io.Copy(stdin, strings.NewReader(stdinCloseTestString))
+		check("Copy", err)
+		// Before the fix, this next line would race with cmd.Wait.
+		check("Close", stdin.Close())
+	}()
+	check("Wait", cmd.Wait())
+}
+
+// Issue 5071
+func TestPipeLookPathLeak(t *testing.T) {
+	fd0, lsof0 := numOpenFDS(t)
+	for i := 0; i < 4; i++ {
+		cmd := exec.Command("something-that-does-not-exist-binary")
+		cmd.StdoutPipe()
+		cmd.StderrPipe()
+		cmd.StdinPipe()
+		if err := cmd.Run(); err == nil {
+			t.Fatal("unexpected success")
+		}
+	}
+	for triesLeft := 3; triesLeft >= 0; triesLeft-- {
+		open, lsof := numOpenFDS(t)
+		fdGrowth := open - fd0
+		if fdGrowth > 2 {
+			if triesLeft > 0 {
+				// Work around what appears to be a race with Linux's
+				// proc filesystem (as used by lsof). It seems to only
+				// be eventually consistent. Give it awhile to settle.
+				// See golang.org/issue/7808
+				time.Sleep(100 * time.Millisecond)
+				continue
+			}
+			t.Errorf("leaked %d fds; want ~0; have:\n%s\noriginally:\n%s", fdGrowth, lsof, lsof0)
+		}
+		break
+	}
+}
+
+func numOpenFDS(t *testing.T) (n int, lsof []byte) {
+	lsof, err := exec.Command("lsof", "-n", "-p", strconv.Itoa(os.Getpid())).Output()
+	if err != nil {
+		t.Skip("skipping test; error finding or running lsof")
+	}
+	return bytes.Count(lsof, []byte("\n")), lsof
+}
+
+var testedAlreadyLeaked = false
+
+// basefds returns the number of expected file descriptors
+// to be present in a process at start.
+func basefds() uintptr {
+	n := os.Stderr.Fd() + 1
+
+	// Go runtime for 32-bit Plan 9 requires that /dev/bintime
+	// be kept open.
+	// See ../../runtime/time_plan9_386.c:/^runtime·nanotime
+	if runtime.GOOS == "plan9" && runtime.GOARCH == "386" {
+		n++
+	}
+	return n
+}
+
+func closeUnexpectedFds(t *testing.T, m string) {
+	for fd := basefds(); fd <= 101; fd++ {
+		err := os.NewFile(fd, "").Close()
+		if err == nil {
+			t.Logf("%s: Something already leaked - closed fd %d", m, fd)
+		}
+	}
+}
+
+func TestExtraFilesFDShuffle(t *testing.T) {
+	t.Skip("flaky test; see http://golang.org/issue/5780")
+	switch runtime.GOOS {
+	case "darwin":
+		// TODO(cnicolaou): http://golang.org/issue/2603
+		// leads to leaked file descriptors in this test when it's
+		// run from a builder.
+		closeUnexpectedFds(t, "TestExtraFilesFDShuffle")
+	case "netbsd":
+		// http://golang.org/issue/3955
+		closeUnexpectedFds(t, "TestExtraFilesFDShuffle")
+	case "windows":
+		t.Skip("no operating system support; skipping")
+	}
+
+	// syscall.StartProcess maps all the FDs passed to it in
+	// ProcAttr.Files (the concatenation of stdin,stdout,stderr and
+	// ExtraFiles) into consecutive FDs in the child, that is:
+	// Files{11, 12, 6, 7, 9, 3} should result in the file
+	// represented by FD 11 in the parent being made available as 0
+	// in the child, 12 as 1, etc.
+	//
+	// We want to test that FDs in the child do not get overwritten
+	// by one another as this shuffle occurs. The original implementation
+	// was buggy in that in some data dependent cases it would ovewrite
+	// stderr in the child with one of the ExtraFile members.
+	// Testing for this case is difficult because it relies on using
+	// the same FD values as that case. In particular, an FD of 3
+	// must be at an index of 4 or higher in ProcAttr.Files and
+	// the FD of the write end of the Stderr pipe (as obtained by
+	// StderrPipe()) must be the same as the size of ProcAttr.Files;
+	// therefore we test that the read end of this pipe (which is what
+	// is returned to the parent by StderrPipe() being one less than
+	// the size of ProcAttr.Files, i.e. 3+len(cmd.ExtraFiles).
+	//
+	// Moving this test case around within the overall tests may
+	// affect the FDs obtained and hence the checks to catch these cases.
+	npipes := 2
+	c := helperCommand(t, "extraFilesAndPipes", strconv.Itoa(npipes+1))
+	rd, wr, _ := os.Pipe()
+	defer rd.Close()
+	if rd.Fd() != 3 {
+		t.Errorf("bad test value for test pipe: fd %d", rd.Fd())
+	}
+	stderr, _ := c.StderrPipe()
+	wr.WriteString("_LAST")
+	wr.Close()
+
+	pipes := make([]struct {
+		r, w *os.File
+	}, npipes)
+	data := []string{"a", "b"}
+
+	for i := 0; i < npipes; i++ {
+		r, w, err := os.Pipe()
+		if err != nil {
+			t.Fatalf("unexpected error creating pipe: %s", err)
+		}
+		pipes[i].r = r
+		pipes[i].w = w
+		w.WriteString(data[i])
+		c.ExtraFiles = append(c.ExtraFiles, pipes[i].r)
+		defer func() {
+			r.Close()
+			w.Close()
+		}()
+	}
+	// Put fd 3 at the end.
+	c.ExtraFiles = append(c.ExtraFiles, rd)
+
+	stderrFd := int(stderr.(*os.File).Fd())
+	if stderrFd != ((len(c.ExtraFiles) + 3) - 1) {
+		t.Errorf("bad test value for stderr pipe")
+	}
+
+	expected := "child: " + strings.Join(data, "") + "_LAST"
+
+	err := c.Start()
+	if err != nil {
+		t.Fatalf("Run: %v", err)
+	}
+	ch := make(chan string, 1)
+	go func(ch chan string) {
+		buf := make([]byte, 512)
+		n, err := stderr.Read(buf)
+		if err != nil {
+			t.Fatalf("Read: %s", err)
+			ch <- err.Error()
+		} else {
+			ch <- string(buf[:n])
+		}
+		close(ch)
+	}(ch)
+	select {
+	case m := <-ch:
+		if m != expected {
+			t.Errorf("Read: '%s' not '%s'", m, expected)
+		}
+	case <-time.After(5 * time.Second):
+		t.Errorf("Read timedout")
+	}
+	c.Wait()
+}
+
+func TestExtraFiles(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("no operating system support; skipping")
+	}
+
+	// Ensure that file descriptors have not already been leaked into
+	// our environment.
+	if !testedAlreadyLeaked {
+		testedAlreadyLeaked = true
+		closeUnexpectedFds(t, "TestExtraFiles")
+	}
+
+	// Force network usage, to verify the epoll (or whatever) fd
+	// doesn't leak to the child,
+	ln, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer ln.Close()
+
+	// Make sure duplicated fds don't leak to the child.
+	f, err := ln.(*net.TCPListener).File()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+	ln2, err := net.FileListener(f)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer ln2.Close()
+
+	// Force TLS root certs to be loaded (which might involve
+	// cgo), to make sure none of that potential C code leaks fds.
+	ts := httptest.NewUnstartedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {}))
+	// quiet expected TLS handshake error "remote error: bad certificate"
+	ts.Config.ErrorLog = log.New(ioutil.Discard, "", 0)
+	ts.StartTLS()
+	defer ts.Close()
+	_, err = http.Get(ts.URL)
+	if err == nil {
+		t.Errorf("success trying to fetch %s; want an error", ts.URL)
+	}
+
+	tf, err := ioutil.TempFile("", "")
+	if err != nil {
+		t.Fatalf("TempFile: %v", err)
+	}
+	defer os.Remove(tf.Name())
+	defer tf.Close()
+
+	const text = "Hello, fd 3!"
+	_, err = tf.Write([]byte(text))
+	if err != nil {
+		t.Fatalf("Write: %v", err)
+	}
+	_, err = tf.Seek(0, os.SEEK_SET)
+	if err != nil {
+		t.Fatalf("Seek: %v", err)
+	}
+
+	c := helperCommand(t, "read3")
+	var stdout, stderr bytes.Buffer
+	c.Stdout = &stdout
+	c.Stderr = &stderr
+	c.ExtraFiles = []*os.File{tf}
+	err = c.Run()
+	if err != nil {
+		t.Fatalf("Run: %v; stdout %q, stderr %q", err, stdout.Bytes(), stderr.Bytes())
+	}
+	if stdout.String() != text {
+		t.Errorf("got stdout %q, stderr %q; want %q on stdout", stdout.String(), stderr.String(), text)
+	}
+}
+
+func TestExtraFilesRace(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("no operating system support; skipping")
+	}
+	listen := func() net.Listener {
+		ln, err := net.Listen("tcp", "127.0.0.1:0")
+		if err != nil {
+			t.Fatal(err)
+		}
+		return ln
+	}
+	listenerFile := func(ln net.Listener) *os.File {
+		f, err := ln.(*net.TCPListener).File()
+		if err != nil {
+			t.Fatal(err)
+		}
+		return f
+	}
+	runCommand := func(c *exec.Cmd, out chan<- string) {
+		bout, err := c.CombinedOutput()
+		if err != nil {
+			out <- "ERROR:" + err.Error()
+		} else {
+			out <- string(bout)
+		}
+	}
+
+	for i := 0; i < 10; i++ {
+		la := listen()
+		ca := helperCommand(t, "describefiles")
+		ca.ExtraFiles = []*os.File{listenerFile(la)}
+		lb := listen()
+		cb := helperCommand(t, "describefiles")
+		cb.ExtraFiles = []*os.File{listenerFile(lb)}
+		ares := make(chan string)
+		bres := make(chan string)
+		go runCommand(ca, ares)
+		go runCommand(cb, bres)
+		if got, want := <-ares, fmt.Sprintf("fd3: listener %s\n", la.Addr()); got != want {
+			t.Errorf("iteration %d, process A got:\n%s\nwant:\n%s\n", i, got, want)
+		}
+		if got, want := <-bres, fmt.Sprintf("fd3: listener %s\n", lb.Addr()); got != want {
+			t.Errorf("iteration %d, process B got:\n%s\nwant:\n%s\n", i, got, want)
+		}
+		la.Close()
+		lb.Close()
+		for _, f := range ca.ExtraFiles {
+			f.Close()
+		}
+		for _, f := range cb.ExtraFiles {
+			f.Close()
+		}
+
+	}
+}
+
+// TestHelperProcess isn't a real test. It's used as a helper process
+// for TestParameterRun.
+func TestHelperProcess(*testing.T) {
+	if os.Getenv("GO_WANT_HELPER_PROCESS") != "1" {
+		return
+	}
+	defer os.Exit(0)
+
+	// Determine which command to use to display open files.
+	ofcmd := "lsof"
+	switch runtime.GOOS {
+	case "dragonfly", "freebsd", "netbsd", "openbsd":
+		ofcmd = "fstat"
+	case "plan9":
+		ofcmd = "/bin/cat"
+	}
+
+	args := os.Args
+	for len(args) > 0 {
+		if args[0] == "--" {
+			args = args[1:]
+			break
+		}
+		args = args[1:]
+	}
+	if len(args) == 0 {
+		fmt.Fprintf(os.Stderr, "No command\n")
+		os.Exit(2)
+	}
+
+	cmd, args := args[0], args[1:]
+	switch cmd {
+	case "echo":
+		iargs := []interface{}{}
+		for _, s := range args {
+			iargs = append(iargs, s)
+		}
+		fmt.Println(iargs...)
+	case "cat":
+		if len(args) == 0 {
+			io.Copy(os.Stdout, os.Stdin)
+			return
+		}
+		exit := 0
+		for _, fn := range args {
+			f, err := os.Open(fn)
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+				exit = 2
+			} else {
+				defer f.Close()
+				io.Copy(os.Stdout, f)
+			}
+		}
+		os.Exit(exit)
+	case "pipetest":
+		bufr := bufio.NewReader(os.Stdin)
+		for {
+			line, _, err := bufr.ReadLine()
+			if err == io.EOF {
+				break
+			} else if err != nil {
+				os.Exit(1)
+			}
+			if bytes.HasPrefix(line, []byte("O:")) {
+				os.Stdout.Write(line)
+				os.Stdout.Write([]byte{'\n'})
+			} else if bytes.HasPrefix(line, []byte("E:")) {
+				os.Stderr.Write(line)
+				os.Stderr.Write([]byte{'\n'})
+			} else {
+				os.Exit(1)
+			}
+		}
+	case "stdinClose":
+		b, err := ioutil.ReadAll(os.Stdin)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+			os.Exit(1)
+		}
+		if s := string(b); s != stdinCloseTestString {
+			fmt.Fprintf(os.Stderr, "Error: Read %q, want %q", s, stdinCloseTestString)
+			os.Exit(1)
+		}
+		os.Exit(0)
+	case "read3": // read fd 3
+		fd3 := os.NewFile(3, "fd3")
+		bs, err := ioutil.ReadAll(fd3)
+		if err != nil {
+			fmt.Printf("ReadAll from fd 3: %v", err)
+			os.Exit(1)
+		}
+		switch runtime.GOOS {
+		case "dragonfly":
+			// TODO(jsing): Determine why DragonFly is leaking
+			// file descriptors...
+		case "darwin":
+			// TODO(bradfitz): broken? Sometimes.
+			// http://golang.org/issue/2603
+			// Skip this additional part of the test for now.
+		case "netbsd":
+			// TODO(jsing): This currently fails on NetBSD due to
+			// the cloned file descriptors that result from opening
+			// /dev/urandom.
+			// http://golang.org/issue/3955
+		case "plan9":
+			// TODO(0intro): Determine why Plan 9 is leaking
+			// file descriptors.
+			// http://golang.org/issue/7118
+		case "solaris":
+			// TODO(aram): This fails on Solaris because libc opens
+			// its own files, as it sees fit. Darwin does the same,
+			// see: http://golang.org/issue/2603
+		default:
+			// Now verify that there are no other open fds.
+			var files []*os.File
+			for wantfd := basefds() + 1; wantfd <= 100; wantfd++ {
+				f, err := os.Open(os.Args[0])
+				if err != nil {
+					fmt.Printf("error opening file with expected fd %d: %v", wantfd, err)
+					os.Exit(1)
+				}
+				if got := f.Fd(); got != wantfd {
+					fmt.Printf("leaked parent file. fd = %d; want %d\n", got, wantfd)
+					var args []string
+					switch runtime.GOOS {
+					case "plan9":
+						args = []string{fmt.Sprintf("/proc/%d/fd", os.Getpid())}
+					default:
+						args = []string{"-p", fmt.Sprint(os.Getpid())}
+					}
+					out, _ := exec.Command(ofcmd, args...).CombinedOutput()
+					fmt.Print(string(out))
+					os.Exit(1)
+				}
+				files = append(files, f)
+			}
+			for _, f := range files {
+				f.Close()
+			}
+		}
+		// Referring to fd3 here ensures that it is not
+		// garbage collected, and therefore closed, while
+		// executing the wantfd loop above.  It doesn't matter
+		// what we do with fd3 as long as we refer to it;
+		// closing it is the easy choice.
+		fd3.Close()
+		os.Stdout.Write(bs)
+	case "exit":
+		n, _ := strconv.Atoi(args[0])
+		os.Exit(n)
+	case "describefiles":
+		f := os.NewFile(3, fmt.Sprintf("fd3"))
+		ln, err := net.FileListener(f)
+		if err == nil {
+			fmt.Printf("fd3: listener %s\n", ln.Addr())
+			ln.Close()
+		}
+		os.Exit(0)
+	case "extraFilesAndPipes":
+		n, _ := strconv.Atoi(args[0])
+		pipes := make([]*os.File, n)
+		for i := 0; i < n; i++ {
+			pipes[i] = os.NewFile(uintptr(3+i), strconv.Itoa(i))
+		}
+		response := ""
+		for i, r := range pipes {
+			ch := make(chan string, 1)
+			go func(c chan string) {
+				buf := make([]byte, 10)
+				n, err := r.Read(buf)
+				if err != nil {
+					fmt.Fprintf(os.Stderr, "Child: read error: %v on pipe %d\n", err, i)
+					os.Exit(1)
+				}
+				c <- string(buf[:n])
+				close(c)
+			}(ch)
+			select {
+			case m := <-ch:
+				response = response + m
+			case <-time.After(5 * time.Second):
+				fmt.Fprintf(os.Stderr, "Child: Timeout reading from pipe: %d\n", i)
+				os.Exit(1)
+			}
+		}
+		fmt.Fprintf(os.Stderr, "child: %s", response)
+		os.Exit(0)
+	case "exec":
+		cmd := exec.Command(args[1])
+		cmd.Dir = args[0]
+		output, err := cmd.CombinedOutput()
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "Child: %s %s", err, string(output))
+			os.Exit(1)
+		}
+		fmt.Printf("%s", string(output))
+		os.Exit(0)
+	case "lookpath":
+		p, err := exec.LookPath(args[0])
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "LookPath failed: %v\n", err)
+			os.Exit(1)
+		}
+		fmt.Print(p)
+		os.Exit(0)
+	default:
+		fmt.Fprintf(os.Stderr, "Unknown command %q\n", cmd)
+		os.Exit(2)
+	}
+}
diff --git a/src/os/exec/lp_plan9.go b/src/os/exec/lp_plan9.go
new file mode 100644
index 000000000..5aa8a54ed
--- /dev/null
+++ b/src/os/exec/lp_plan9.go
@@ -0,0 +1,53 @@
+// Copyright 2011 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 exec
+
+import (
+	"errors"
+	"os"
+	"strings"
+)
+
+// ErrNotFound is the error resulting if a path search failed to find an executable file.
+var ErrNotFound = errors.New("executable file not found in $path")
+
+func findExecutable(file string) error {
+	d, err := os.Stat(file)
+	if err != nil {
+		return err
+	}
+	if m := d.Mode(); !m.IsDir() && m&0111 != 0 {
+		return nil
+	}
+	return os.ErrPermission
+}
+
+// LookPath searches for an executable binary named file
+// in the directories named by the path environment variable.
+// If file begins with "/", "#", "./", or "../", it is tried
+// directly and the path is not consulted.
+// The result may be an absolute path or a path relative to the current directory.
+func LookPath(file string) (string, error) {
+	// skip the path lookup for these prefixes
+	skip := []string{"/", "#", "./", "../"}
+
+	for _, p := range skip {
+		if strings.HasPrefix(file, p) {
+			err := findExecutable(file)
+			if err == nil {
+				return file, nil
+			}
+			return "", &Error{file, err}
+		}
+	}
+
+	path := os.Getenv("path")
+	for _, dir := range strings.Split(path, "\000") {
+		if err := findExecutable(dir + "/" + file); err == nil {
+			return dir + "/" + file, nil
+		}
+	}
+	return "", &Error{file, ErrNotFound}
+}
diff --git a/src/os/exec/lp_test.go b/src/os/exec/lp_test.go
new file mode 100644
index 000000000..77d8e848c
--- /dev/null
+++ b/src/os/exec/lp_test.go
@@ -0,0 +1,33 @@
+// Copyright 2011 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 exec
+
+import (
+	"testing"
+)
+
+var nonExistentPaths = []string{
+	"some-non-existent-path",
+	"non-existent-path/slashed",
+}
+
+func TestLookPathNotFound(t *testing.T) {
+	for _, name := range nonExistentPaths {
+		path, err := LookPath(name)
+		if err == nil {
+			t.Fatalf("LookPath found %q in $PATH", name)
+		}
+		if path != "" {
+			t.Fatalf("LookPath path == %q when err != nil", path)
+		}
+		perr, ok := err.(*Error)
+		if !ok {
+			t.Fatal("LookPath error is not an exec.Error")
+		}
+		if perr.Name != name {
+			t.Fatalf("want Error name %q, got %q", name, perr.Name)
+		}
+	}
+}
diff --git a/src/os/exec/lp_unix.go b/src/os/exec/lp_unix.go
new file mode 100644
index 000000000..3f895d5b3
--- /dev/null
+++ b/src/os/exec/lp_unix.go
@@ -0,0 +1,60 @@
+// Copyright 2010 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.
+
+// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
+
+package exec
+
+import (
+	"errors"
+	"os"
+	"strings"
+)
+
+// ErrNotFound is the error resulting if a path search failed to find an executable file.
+var ErrNotFound = errors.New("executable file not found in $PATH")
+
+func findExecutable(file string) error {
+	d, err := os.Stat(file)
+	if err != nil {
+		return err
+	}
+	if m := d.Mode(); !m.IsDir() && m&0111 != 0 {
+		return nil
+	}
+	return os.ErrPermission
+}
+
+// LookPath searches for an executable binary named file
+// in the directories named by the PATH environment variable.
+// If file contains a slash, it is tried directly and the PATH is not consulted.
+// The result may be an absolute path or a path relative to the current directory.
+func LookPath(file string) (string, error) {
+	// NOTE(rsc): I wish we could use the Plan 9 behavior here
+	// (only bypass the path if file begins with / or ./ or ../)
+	// but that would not match all the Unix shells.
+
+	if strings.Contains(file, "/") {
+		err := findExecutable(file)
+		if err == nil {
+			return file, nil
+		}
+		return "", &Error{file, err}
+	}
+	pathenv := os.Getenv("PATH")
+	if pathenv == "" {
+		return "", &Error{file, ErrNotFound}
+	}
+	for _, dir := range strings.Split(pathenv, ":") {
+		if dir == "" {
+			// Unix shell semantics: path element "" means "."
+			dir = "."
+		}
+		path := dir + "/" + file
+		if err := findExecutable(path); err == nil {
+			return path, nil
+		}
+	}
+	return "", &Error{file, ErrNotFound}
+}
diff --git a/src/os/exec/lp_unix_test.go b/src/os/exec/lp_unix_test.go
new file mode 100644
index 000000000..051db664a
--- /dev/null
+++ b/src/os/exec/lp_unix_test.go
@@ -0,0 +1,55 @@
+// Copyright 2013 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.
+
+// +build darwin dragonfly freebsd linux netbsd openbsd solaris
+
+package exec
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+)
+
+func TestLookPathUnixEmptyPath(t *testing.T) {
+	tmp, err := ioutil.TempDir("", "TestLookPathUnixEmptyPath")
+	if err != nil {
+		t.Fatal("TempDir failed: ", err)
+	}
+	defer os.RemoveAll(tmp)
+	wd, err := os.Getwd()
+	if err != nil {
+		t.Fatal("Getwd failed: ", err)
+	}
+	err = os.Chdir(tmp)
+	if err != nil {
+		t.Fatal("Chdir failed: ", err)
+	}
+	defer os.Chdir(wd)
+
+	f, err := os.OpenFile("exec_me", os.O_CREATE|os.O_EXCL, 0700)
+	if err != nil {
+		t.Fatal("OpenFile failed: ", err)
+	}
+	err = f.Close()
+	if err != nil {
+		t.Fatal("Close failed: ", err)
+	}
+
+	pathenv := os.Getenv("PATH")
+	defer os.Setenv("PATH", pathenv)
+
+	err = os.Setenv("PATH", "")
+	if err != nil {
+		t.Fatal("Setenv failed: ", err)
+	}
+
+	path, err := LookPath("exec_me")
+	if err == nil {
+		t.Fatal("LookPath found exec_me in empty $PATH")
+	}
+	if path != "" {
+		t.Fatalf("LookPath path == %q when err != nil", path)
+	}
+}
diff --git a/src/os/exec/lp_windows.go b/src/os/exec/lp_windows.go
new file mode 100644
index 000000000..c3efd67e9
--- /dev/null
+++ b/src/os/exec/lp_windows.go
@@ -0,0 +1,123 @@
+// Copyright 2010 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 exec
+
+import (
+	"errors"
+	"os"
+	"strings"
+)
+
+// ErrNotFound is the error resulting if a path search failed to find an executable file.
+var ErrNotFound = errors.New("executable file not found in %PATH%")
+
+func chkStat(file string) error {
+	d, err := os.Stat(file)
+	if err != nil {
+		return err
+	}
+	if d.IsDir() {
+		return os.ErrPermission
+	}
+	return nil
+}
+
+func hasExt(file string) bool {
+	i := strings.LastIndex(file, ".")
+	if i < 0 {
+		return false
+	}
+	return strings.LastIndexAny(file, `:\/`) < i
+}
+
+func findExecutable(file string, exts []string) (string, error) {
+	if len(exts) == 0 {
+		return file, chkStat(file)
+	}
+	if hasExt(file) {
+		if chkStat(file) == nil {
+			return file, nil
+		}
+	}
+	for _, e := range exts {
+		if f := file + e; chkStat(f) == nil {
+			return f, nil
+		}
+	}
+	return ``, os.ErrNotExist
+}
+
+// LookPath searches for an executable binary named file
+// in the directories named by the PATH environment variable.
+// If file contains a slash, it is tried directly and the PATH is not consulted.
+// LookPath also uses PATHEXT environment variable to match
+// a suitable candidate.
+// The result may be an absolute path or a path relative to the current directory.
+func LookPath(file string) (f string, err error) {
+	x := os.Getenv(`PATHEXT`)
+	if x == `` {
+		x = `.COM;.EXE;.BAT;.CMD`
+	}
+	exts := []string{}
+	for _, e := range strings.Split(strings.ToLower(x), `;`) {
+		if e == "" {
+			continue
+		}
+		if e[0] != '.' {
+			e = "." + e
+		}
+		exts = append(exts, e)
+	}
+	if strings.IndexAny(file, `:\/`) != -1 {
+		if f, err = findExecutable(file, exts); err == nil {
+			return
+		}
+		return ``, &Error{file, err}
+	}
+	if f, err = findExecutable(`.\`+file, exts); err == nil {
+		return
+	}
+	if pathenv := os.Getenv(`PATH`); pathenv != `` {
+		for _, dir := range splitList(pathenv) {
+			if f, err = findExecutable(dir+`\`+file, exts); err == nil {
+				return
+			}
+		}
+	}
+	return ``, &Error{file, ErrNotFound}
+}
+
+func splitList(path string) []string {
+	// The same implementation is used in SplitList in path/filepath;
+	// consider changing path/filepath when changing this.
+
+	if path == "" {
+		return []string{}
+	}
+
+	// Split path, respecting but preserving quotes.
+	list := []string{}
+	start := 0
+	quo := false
+	for i := 0; i < len(path); i++ {
+		switch c := path[i]; {
+		case c == '"':
+			quo = !quo
+		case c == os.PathListSeparator && !quo:
+			list = append(list, path[start:i])
+			start = i + 1
+		}
+	}
+	list = append(list, path[start:])
+
+	// Remove quotes.
+	for i, s := range list {
+		if strings.Contains(s, `"`) {
+			list[i] = strings.Replace(s, `"`, ``, -1)
+		}
+	}
+
+	return list
+}
diff --git a/src/os/exec/lp_windows_test.go b/src/os/exec/lp_windows_test.go
new file mode 100644
index 000000000..72df03ed2
--- /dev/null
+++ b/src/os/exec/lp_windows_test.go
@@ -0,0 +1,573 @@
+// Copyright 2013 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 exec
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+func installExe(t *testing.T, dest, src string) {
+	fsrc, err := os.Open(src)
+	if err != nil {
+		t.Fatal("os.Open failed: ", err)
+	}
+	defer fsrc.Close()
+	fdest, err := os.Create(dest)
+	if err != nil {
+		t.Fatal("os.Create failed: ", err)
+	}
+	defer fdest.Close()
+	_, err = io.Copy(fdest, fsrc)
+	if err != nil {
+		t.Fatal("io.Copy failed: ", err)
+	}
+}
+
+func installBat(t *testing.T, dest string) {
+	f, err := os.Create(dest)
+	if err != nil {
+		t.Fatalf("failed to create batch file: %v", err)
+	}
+	defer f.Close()
+	fmt.Fprintf(f, "@echo %s\n", dest)
+}
+
+func installProg(t *testing.T, dest, srcExe string) {
+	err := os.MkdirAll(filepath.Dir(dest), 0700)
+	if err != nil {
+		t.Fatal("os.MkdirAll failed: ", err)
+	}
+	if strings.ToLower(filepath.Ext(dest)) == ".bat" {
+		installBat(t, dest)
+		return
+	}
+	installExe(t, dest, srcExe)
+}
+
+type lookPathTest struct {
+	rootDir   string
+	PATH      string
+	PATHEXT   string
+	files     []string
+	searchFor string
+	fails     bool // test is expected to fail
+}
+
+func (test lookPathTest) runProg(t *testing.T, env []string, args ...string) (string, error) {
+	cmd := Command(args[0], args[1:]...)
+	cmd.Env = env
+	cmd.Dir = test.rootDir
+	args[0] = filepath.Base(args[0])
+	cmdText := fmt.Sprintf("%q command", strings.Join(args, " "))
+	out, err := cmd.CombinedOutput()
+	if (err != nil) != test.fails {
+		if test.fails {
+			t.Fatalf("test=%+v: %s succeeded, but expected to fail", test, cmdText)
+		}
+		t.Fatalf("test=%+v: %s failed, but expected to succeed: %v - %v", test, cmdText, err, string(out))
+	}
+	if err != nil {
+		return "", fmt.Errorf("test=%+v: %s failed: %v - %v", test, cmdText, err, string(out))
+	}
+	// normalise program output
+	p := string(out)
+	// trim terminating \r and \n that batch file outputs
+	for len(p) > 0 && (p[len(p)-1] == '\n' || p[len(p)-1] == '\r') {
+		p = p[:len(p)-1]
+	}
+	if !filepath.IsAbs(p) {
+		return p, nil
+	}
+	if p[:len(test.rootDir)] != test.rootDir {
+		t.Fatalf("test=%+v: %s output is wrong: %q must have %q prefix", test, cmdText, p, test.rootDir)
+	}
+	return p[len(test.rootDir)+1:], nil
+}
+
+func updateEnv(env []string, name, value string) []string {
+	for i, e := range env {
+		if strings.HasPrefix(strings.ToUpper(e), name+"=") {
+			env[i] = name + "=" + value
+			return env
+		}
+	}
+	return append(env, name+"="+value)
+}
+
+func createEnv(dir, PATH, PATHEXT string) []string {
+	env := os.Environ()
+	env = updateEnv(env, "PATHEXT", PATHEXT)
+	// Add dir in front of every directory in the PATH.
+	dirs := splitList(PATH)
+	for i := range dirs {
+		dirs[i] = filepath.Join(dir, dirs[i])
+	}
+	path := strings.Join(dirs, ";")
+	env = updateEnv(env, "PATH", path)
+	return env
+}
+
+// createFiles copies srcPath file into multiply files.
+// It uses dir as preifx for all destination files.
+func createFiles(t *testing.T, dir string, files []string, srcPath string) {
+	for _, f := range files {
+		installProg(t, filepath.Join(dir, f), srcPath)
+	}
+}
+
+func (test lookPathTest) run(t *testing.T, tmpdir, printpathExe string) {
+	test.rootDir = tmpdir
+	createFiles(t, test.rootDir, test.files, printpathExe)
+	env := createEnv(test.rootDir, test.PATH, test.PATHEXT)
+	// Run "cmd.exe /c test.searchFor" with new environment and
+	// work directory set. All candidates are copies of printpath.exe.
+	// These will output their program paths when run.
+	should, errCmd := test.runProg(t, env, "cmd", "/c", test.searchFor)
+	// Run the lookpath program with new environment and work directory set.
+	env = append(env, "GO_WANT_HELPER_PROCESS=1")
+	have, errLP := test.runProg(t, env, os.Args[0], "-test.run=TestHelperProcess", "--", "lookpath", test.searchFor)
+	// Compare results.
+	if errCmd == nil && errLP == nil {
+		// both succeeded
+		if should != have {
+			t.Fatalf("test=%+v failed: expected to find %q, but found %q", test, should, have)
+		}
+		return
+	}
+	if errCmd != nil && errLP != nil {
+		// both failed -> continue
+		return
+	}
+	if errCmd != nil {
+		t.Fatal(errCmd)
+	}
+	if errLP != nil {
+		t.Fatal(errLP)
+	}
+}
+
+var lookPathTests = []lookPathTest{
+	{
+		PATHEXT:   `.COM;.EXE;.BAT`,
+		PATH:      `p1;p2`,
+		files:     []string{`p1\a.exe`, `p2\a.exe`, `p2\a`},
+		searchFor: `a`,
+	},
+	{
+		PATHEXT:   `.COM;.EXE;.BAT`,
+		PATH:      `p1.dir;p2.dir`,
+		files:     []string{`p1.dir\a`, `p2.dir\a.exe`},
+		searchFor: `a`,
+	},
+	{
+		PATHEXT:   `.COM;.EXE;.BAT`,
+		PATH:      `p1;p2`,
+		files:     []string{`p1\a.exe`, `p2\a.exe`},
+		searchFor: `a.exe`,
+	},
+	{
+		PATHEXT:   `.COM;.EXE;.BAT`,
+		PATH:      `p1;p2`,
+		files:     []string{`p1\a.exe`, `p2\b.exe`},
+		searchFor: `b`,
+	},
+	{
+		PATHEXT:   `.COM;.EXE;.BAT`,
+		PATH:      `p1;p2`,
+		files:     []string{`p1\b`, `p2\a`},
+		searchFor: `a`,
+		fails:     true, // TODO(brainman): do not know why this fails
+	},
+	// If the command name specifies a path, the shell searches
+	// the specified path for an executable file matching
+	// the command name. If a match is found, the external
+	// command (the executable file) executes.
+	{
+		PATHEXT:   `.COM;.EXE;.BAT`,
+		PATH:      `p1;p2`,
+		files:     []string{`p1\a.exe`, `p2\a.exe`},
+		searchFor: `p2\a`,
+	},
+	// If the command name specifies a path, the shell searches
+	// the specified path for an executable file matching the command
+	// name. ... If no match is found, the shell reports an error
+	// and command processing completes.
+	{
+		PATHEXT:   `.COM;.EXE;.BAT`,
+		PATH:      `p1;p2`,
+		files:     []string{`p1\b.exe`, `p2\a.exe`},
+		searchFor: `p2\b`,
+		fails:     true,
+	},
+	// If the command name does not specify a path, the shell
+	// searches the current directory for an executable file
+	// matching the command name. If a match is found, the external
+	// command (the executable file) executes.
+	{
+		PATHEXT:   `.COM;.EXE;.BAT`,
+		PATH:      `p1;p2`,
+		files:     []string{`a`, `p1\a.exe`, `p2\a.exe`},
+		searchFor: `a`,
+	},
+	// The shell now searches each directory specified by the
+	// PATH environment variable, in the order listed, for an
+	// executable file matching the command name. If a match
+	// is found, the external command (the executable file) executes.
+	{
+		PATHEXT:   `.COM;.EXE;.BAT`,
+		PATH:      `p1;p2`,
+		files:     []string{`p1\a.exe`, `p2\a.exe`},
+		searchFor: `a`,
+	},
+	// The shell now searches each directory specified by the
+	// PATH environment variable, in the order listed, for an
+	// executable file matching the command name. If no match
+	// is found, the shell reports an error and command processing
+	// completes.
+	{
+		PATHEXT:   `.COM;.EXE;.BAT`,
+		PATH:      `p1;p2`,
+		files:     []string{`p1\a.exe`, `p2\a.exe`},
+		searchFor: `b`,
+		fails:     true,
+	},
+	// If the command name includes a file extension, the shell
+	// searches each directory for the exact file name specified
+	// by the command name.
+	{
+		PATHEXT:   `.COM;.EXE;.BAT`,
+		PATH:      `p1;p2`,
+		files:     []string{`p1\a.exe`, `p2\a.exe`},
+		searchFor: `a.exe`,
+	},
+	{
+		PATHEXT:   `.COM;.EXE;.BAT`,
+		PATH:      `p1;p2`,
+		files:     []string{`p1\a.exe`, `p2\a.exe`},
+		searchFor: `a.com`,
+		fails:     true, // includes extension and not exact file name match
+	},
+	{
+		PATHEXT:   `.COM;.EXE;.BAT`,
+		PATH:      `p1`,
+		files:     []string{`p1\a.exe.exe`},
+		searchFor: `a.exe`,
+	},
+	{
+		PATHEXT:   `.COM;.BAT`,
+		PATH:      `p1;p2`,
+		files:     []string{`p1\a.exe`, `p2\a.exe`},
+		searchFor: `a.exe`,
+	},
+	// If the command name does not include a file extension, the shell
+	// adds the extensions listed in the PATHEXT environment variable,
+	// one by one, and searches the directory for that file name. Note
+	// that the shell tries all possible file extensions in a specific
+	// directory before moving on to search the next directory
+	// (if there is one).
+	{
+		PATHEXT:   `.COM;.EXE`,
+		PATH:      `p1;p2`,
+		files:     []string{`p1\a.bat`, `p2\a.exe`},
+		searchFor: `a`,
+	},
+	{
+		PATHEXT:   `.COM;.EXE;.BAT`,
+		PATH:      `p1;p2`,
+		files:     []string{`p1\a.bat`, `p2\a.exe`},
+		searchFor: `a`,
+	},
+	{
+		PATHEXT:   `.COM;.EXE;.BAT`,
+		PATH:      `p1;p2`,
+		files:     []string{`p1\a.bat`, `p1\a.exe`, `p2\a.bat`, `p2\a.exe`},
+		searchFor: `a`,
+	},
+	{
+		PATHEXT:   `.COM`,
+		PATH:      `p1;p2`,
+		files:     []string{`p1\a.bat`, `p2\a.exe`},
+		searchFor: `a`,
+		fails:     true, // tried all extensions in PATHEXT, but none matches
+	},
+}
+
+func TestLookPath(t *testing.T) {
+	tmp, err := ioutil.TempDir("", "TestLookPath")
+	if err != nil {
+		t.Fatal("TempDir failed: ", err)
+	}
+	defer os.RemoveAll(tmp)
+
+	printpathExe := buildPrintPathExe(t, tmp)
+
+	// Run all tests.
+	for i, test := range lookPathTests {
+		dir := filepath.Join(tmp, "d"+strconv.Itoa(i))
+		err := os.Mkdir(dir, 0700)
+		if err != nil {
+			t.Fatal("Mkdir failed: ", err)
+		}
+		test.run(t, dir, printpathExe)
+	}
+}
+
+type commandTest struct {
+	PATH  string
+	files []string
+	dir   string
+	arg0  string
+	want  string
+	fails bool // test is expected to fail
+}
+
+func (test commandTest) isSuccess(rootDir, output string, err error) error {
+	if err != nil {
+		return fmt.Errorf("test=%+v: exec: %v %v", test, err, output)
+	}
+	path := output
+	if path[:len(rootDir)] != rootDir {
+		return fmt.Errorf("test=%+v: %q must have %q prefix", test, path, rootDir)
+	}
+	path = path[len(rootDir)+1:]
+	if path != test.want {
+		return fmt.Errorf("test=%+v: want %q, got %q", test, test.want, path)
+	}
+	return nil
+}
+
+func (test commandTest) runOne(rootDir string, env []string, dir, arg0 string) error {
+	cmd := Command(os.Args[0], "-test.run=TestHelperProcess", "--", "exec", dir, arg0)
+	cmd.Dir = rootDir
+	cmd.Env = env
+	output, err := cmd.CombinedOutput()
+	err = test.isSuccess(rootDir, string(output), err)
+	if (err != nil) != test.fails {
+		if test.fails {
+			return fmt.Errorf("test=%+v: succeeded, but expected to fail", test)
+		}
+		return err
+	}
+	return nil
+}
+
+func (test commandTest) run(t *testing.T, rootDir, printpathExe string) {
+	createFiles(t, rootDir, test.files, printpathExe)
+	PATHEXT := `.COM;.EXE;.BAT`
+	env := createEnv(rootDir, test.PATH, PATHEXT)
+	env = append(env, "GO_WANT_HELPER_PROCESS=1")
+	err := test.runOne(rootDir, env, test.dir, test.arg0)
+	if err != nil {
+		t.Error(err)
+	}
+}
+
+var commandTests = []commandTest{
+	// testing commands with no slash, like `a.exe`
+	{
+		// should find a.exe in current directory
+		files: []string{`a.exe`},
+		arg0:  `a.exe`,
+		want:  `a.exe`,
+	},
+	{
+		// like above, but add PATH in attempt to break the test
+		PATH:  `p2;p`,
+		files: []string{`a.exe`, `p\a.exe`, `p2\a.exe`},
+		arg0:  `a.exe`,
+		want:  `a.exe`,
+	},
+	{
+		// like above, but use "a" instead of "a.exe" for command
+		PATH:  `p2;p`,
+		files: []string{`a.exe`, `p\a.exe`, `p2\a.exe`},
+		arg0:  `a`,
+		want:  `a.exe`,
+	},
+	// testing commands with slash, like `.\a.exe`
+	{
+		// should find p\a.exe
+		files: []string{`p\a.exe`},
+		arg0:  `p\a.exe`,
+		want:  `p\a.exe`,
+	},
+	{
+		// like above, but adding `.` in front of executable should still be OK
+		files: []string{`p\a.exe`},
+		arg0:  `.\p\a.exe`,
+		want:  `p\a.exe`,
+	},
+	{
+		// like above, but with PATH added in attempt to break it
+		PATH:  `p2`,
+		files: []string{`p\a.exe`, `p2\a.exe`},
+		arg0:  `p\a.exe`,
+		want:  `p\a.exe`,
+	},
+	{
+		// like above, but make sure .exe is tried even for commands with slash
+		PATH:  `p2`,
+		files: []string{`p\a.exe`, `p2\a.exe`},
+		arg0:  `p\a`,
+		want:  `p\a.exe`,
+	},
+	// tests commands, like `a.exe`, with c.Dir set
+	{
+		// should not find a.exe in p, becasue LookPath(`a.exe`) will fail
+		files: []string{`p\a.exe`},
+		dir:   `p`,
+		arg0:  `a.exe`,
+		want:  `p\a.exe`,
+		fails: true,
+	},
+	{
+		// LookPath(`a.exe`) will find `.\a.exe`, but prefixing that with
+		// dir `p\a.exe` will refer to not existant file
+		files: []string{`a.exe`, `p\not_important_file`},
+		dir:   `p`,
+		arg0:  `a.exe`,
+		want:  `a.exe`,
+		fails: true,
+	},
+	{
+		// like above, but making test succeed by installing file
+		// in refered destination (so LookPath(`a.exe`) will still
+		// find `.\a.exe`, but we successfully execute `p\a.exe`)
+		files: []string{`a.exe`, `p\a.exe`},
+		dir:   `p`,
+		arg0:  `a.exe`,
+		want:  `p\a.exe`,
+	},
+	{
+		// like above, but add PATH in attempt to break the test
+		PATH:  `p2;p`,
+		files: []string{`a.exe`, `p\a.exe`, `p2\a.exe`},
+		dir:   `p`,
+		arg0:  `a.exe`,
+		want:  `p\a.exe`,
+	},
+	{
+		// like above, but use "a" instead of "a.exe" for command
+		PATH:  `p2;p`,
+		files: []string{`a.exe`, `p\a.exe`, `p2\a.exe`},
+		dir:   `p`,
+		arg0:  `a`,
+		want:  `p\a.exe`,
+	},
+	{
+		// finds `a.exe` in the PATH regardless of dir set
+		// because LookPath returns full path in that case
+		PATH:  `p2;p`,
+		files: []string{`p\a.exe`, `p2\a.exe`},
+		dir:   `p`,
+		arg0:  `a.exe`,
+		want:  `p2\a.exe`,
+	},
+	// tests commands, like `.\a.exe`, with c.Dir set
+	{
+		// should use dir when command is path, like ".\a.exe"
+		files: []string{`p\a.exe`},
+		dir:   `p`,
+		arg0:  `.\a.exe`,
+		want:  `p\a.exe`,
+	},
+	{
+		// like above, but with PATH added in attempt to break it
+		PATH:  `p2`,
+		files: []string{`p\a.exe`, `p2\a.exe`},
+		dir:   `p`,
+		arg0:  `.\a.exe`,
+		want:  `p\a.exe`,
+	},
+	{
+		// like above, but make sure .exe is tried even for commands with slash
+		PATH:  `p2`,
+		files: []string{`p\a.exe`, `p2\a.exe`},
+		dir:   `p`,
+		arg0:  `.\a`,
+		want:  `p\a.exe`,
+	},
+}
+
+func TestCommand(t *testing.T) {
+	tmp, err := ioutil.TempDir("", "TestCommand")
+	if err != nil {
+		t.Fatal("TempDir failed: ", err)
+	}
+	defer os.RemoveAll(tmp)
+
+	printpathExe := buildPrintPathExe(t, tmp)
+
+	// Run all tests.
+	for i, test := range commandTests {
+		dir := filepath.Join(tmp, "d"+strconv.Itoa(i))
+		err := os.Mkdir(dir, 0700)
+		if err != nil {
+			t.Fatal("Mkdir failed: ", err)
+		}
+		test.run(t, dir, printpathExe)
+	}
+}
+
+// buildPrintPathExe creates a Go program that prints its own path.
+// dir is a temp directory where executable will be created.
+// The function returns full path to the created program.
+func buildPrintPathExe(t *testing.T, dir string) string {
+	const name = "printpath"
+	srcname := name + ".go"
+	err := ioutil.WriteFile(filepath.Join(dir, srcname), []byte(printpathSrc), 0644)
+	if err != nil {
+		t.Fatalf("failed to create source: %v", err)
+	}
+	if err != nil {
+		t.Fatalf("failed to execute template: %v", err)
+	}
+	outname := name + ".exe"
+	cmd := Command("go", "build", "-o", outname, srcname)
+	cmd.Dir = dir
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("failed to build executable: %v - %v", err, string(out))
+	}
+	return filepath.Join(dir, outname)
+}
+
+const printpathSrc = `
+package main
+
+import (
+	"os"
+	"syscall"
+	"unicode/utf16"
+	"unsafe"
+)
+
+func getMyName() (string, error) {
+	var sysproc = syscall.MustLoadDLL("kernel32.dll").MustFindProc("GetModuleFileNameW")
+	b := make([]uint16, syscall.MAX_PATH)
+	r, _, err := sysproc.Call(0, uintptr(unsafe.Pointer(&b[0])), uintptr(len(b)))
+	n := uint32(r)
+	if n == 0 {
+		return "", err
+	}
+	return string(utf16.Decode(b[0:n])), nil
+}
+
+func main() {
+	path, err := getMyName()
+	if err != nil {
+		os.Stderr.Write([]byte("getMyName failed: " + err.Error() + "\n"))
+		os.Exit(1)
+	}
+	os.Stdout.Write([]byte(path))
+}
+`
diff --git a/src/os/exec_plan9.go b/src/os/exec_plan9.go
new file mode 100644
index 000000000..676be36ac
--- /dev/null
+++ b/src/os/exec_plan9.go
@@ -0,0 +1,137 @@
+// 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 (
+	"errors"
+	"runtime"
+	"syscall"
+	"time"
+)
+
+// The only signal values guaranteed to be present on all systems
+// are Interrupt (send the process an interrupt) and Kill (force
+// the process to exit).
+var (
+	Interrupt Signal = syscall.Note("interrupt")
+	Kill      Signal = syscall.Note("kill")
+)
+
+func startProcess(name string, argv []string, attr *ProcAttr) (p *Process, err error) {
+	sysattr := &syscall.ProcAttr{
+		Dir: attr.Dir,
+		Env: attr.Env,
+		Sys: attr.Sys,
+	}
+
+	for _, f := range attr.Files {
+		sysattr.Files = append(sysattr.Files, f.Fd())
+	}
+
+	pid, h, e := syscall.StartProcess(name, argv, sysattr)
+	if e != nil {
+		return nil, &PathError{"fork/exec", name, e}
+	}
+
+	return newProcess(pid, h), nil
+}
+
+func (p *Process) writeProcFile(file string, data string) error {
+	f, e := OpenFile("/proc/"+itoa(p.Pid)+"/"+file, O_WRONLY, 0)
+	if e != nil {
+		return e
+	}
+	defer f.Close()
+	_, e = f.Write([]byte(data))
+	return e
+}
+
+func (p *Process) signal(sig Signal) error {
+	if p.done() {
+		return errors.New("os: process already finished")
+	}
+	if e := p.writeProcFile("note", sig.String()); e != nil {
+		return NewSyscallError("signal", e)
+	}
+	return nil
+}
+
+func (p *Process) kill() error {
+	return p.signal(Kill)
+}
+
+func (p *Process) wait() (ps *ProcessState, err error) {
+	var waitmsg syscall.Waitmsg
+
+	if p.Pid == -1 {
+		return nil, ErrInvalid
+	}
+	err = syscall.WaitProcess(p.Pid, &waitmsg)
+	if err != nil {
+		return nil, NewSyscallError("wait", err)
+	}
+
+	p.setDone()
+	ps = &ProcessState{
+		pid:    waitmsg.Pid,
+		status: &waitmsg,
+	}
+	return ps, nil
+}
+
+func (p *Process) release() error {
+	// NOOP for Plan 9.
+	p.Pid = -1
+	// no need for a finalizer anymore
+	runtime.SetFinalizer(p, nil)
+	return nil
+}
+
+func findProcess(pid int) (p *Process, err error) {
+	// NOOP for Plan 9.
+	return newProcess(pid, 0), nil
+}
+
+// ProcessState stores information about a process, as reported by Wait.
+type ProcessState struct {
+	pid    int              // The process's id.
+	status *syscall.Waitmsg // System-dependent status info.
+}
+
+// Pid returns the process id of the exited process.
+func (p *ProcessState) Pid() int {
+	return p.pid
+}
+
+func (p *ProcessState) exited() bool {
+	return p.status.Exited()
+}
+
+func (p *ProcessState) success() bool {
+	return p.status.ExitStatus() == 0
+}
+
+func (p *ProcessState) sys() interface{} {
+	return p.status
+}
+
+func (p *ProcessState) sysUsage() interface{} {
+	return p.status
+}
+
+func (p *ProcessState) userTime() time.Duration {
+	return time.Duration(p.status.Time[0]) * time.Millisecond
+}
+
+func (p *ProcessState) systemTime() time.Duration {
+	return time.Duration(p.status.Time[1]) * time.Millisecond
+}
+
+func (p *ProcessState) String() string {
+	if p == nil {
+		return "<nil>"
+	}
+	return "exit status: " + p.status.Msg
+}
diff --git a/src/os/exec_posix.go b/src/os/exec_posix.go
new file mode 100644
index 000000000..fb9d291e6
--- /dev/null
+++ b/src/os/exec_posix.go
@@ -0,0 +1,134 @@
+// 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.
+
+// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris windows
+
+package os
+
+import (
+	"syscall"
+)
+
+// The only signal values guaranteed to be present on all systems
+// are Interrupt (send the process an interrupt) and Kill (force
+// the process to exit).
+var (
+	Interrupt Signal = syscall.SIGINT
+	Kill      Signal = syscall.SIGKILL
+)
+
+func startProcess(name string, argv []string, attr *ProcAttr) (p *Process, err error) {
+	// If there is no SysProcAttr (ie. no Chroot or changed
+	// UID/GID), double-check existence of the directory we want
+	// to chdir into.  We can make the error clearer this way.
+	if attr != nil && attr.Sys == nil && attr.Dir != "" {
+		if _, err := Stat(attr.Dir); err != nil {
+			pe := err.(*PathError)
+			pe.Op = "chdir"
+			return nil, pe
+		}
+	}
+
+	sysattr := &syscall.ProcAttr{
+		Dir: attr.Dir,
+		Env: attr.Env,
+		Sys: attr.Sys,
+	}
+	if sysattr.Env == nil {
+		sysattr.Env = Environ()
+	}
+	for _, f := range attr.Files {
+		sysattr.Files = append(sysattr.Files, f.Fd())
+	}
+
+	pid, h, e := syscall.StartProcess(name, argv, sysattr)
+	if e != nil {
+		return nil, &PathError{"fork/exec", name, e}
+	}
+	return newProcess(pid, h), nil
+}
+
+func (p *Process) kill() error {
+	return p.Signal(Kill)
+}
+
+// ProcessState stores information about a process, as reported by Wait.
+type ProcessState struct {
+	pid    int                // The process's id.
+	status syscall.WaitStatus // System-dependent status info.
+	rusage *syscall.Rusage
+}
+
+// Pid returns the process id of the exited process.
+func (p *ProcessState) Pid() int {
+	return p.pid
+}
+
+func (p *ProcessState) exited() bool {
+	return p.status.Exited()
+}
+
+func (p *ProcessState) success() bool {
+	return p.status.ExitStatus() == 0
+}
+
+func (p *ProcessState) sys() interface{} {
+	return p.status
+}
+
+func (p *ProcessState) sysUsage() interface{} {
+	return p.rusage
+}
+
+// Convert i to decimal string.
+func itod(i int) string {
+	if i == 0 {
+		return "0"
+	}
+
+	u := uint64(i)
+	if i < 0 {
+		u = -u
+	}
+
+	// Assemble decimal in reverse order.
+	var b [32]byte
+	bp := len(b)
+	for ; u > 0; u /= 10 {
+		bp--
+		b[bp] = byte(u%10) + '0'
+	}
+
+	if i < 0 {
+		bp--
+		b[bp] = '-'
+	}
+
+	return string(b[bp:])
+}
+
+func (p *ProcessState) String() string {
+	if p == nil {
+		return "<nil>"
+	}
+	status := p.Sys().(syscall.WaitStatus)
+	res := ""
+	switch {
+	case status.Exited():
+		res = "exit status " + itod(status.ExitStatus())
+	case status.Signaled():
+		res = "signal: " + status.Signal().String()
+	case status.Stopped():
+		res = "stop signal: " + status.StopSignal().String()
+		if status.StopSignal() == syscall.SIGTRAP && status.TrapCause() != 0 {
+			res += " (trap " + itod(status.TrapCause()) + ")"
+		}
+	case status.Continued():
+		res = "continued"
+	}
+	if status.CoreDump() {
+		res += " (core dumped)"
+	}
+	return res
+}
diff --git a/src/os/exec_unix.go b/src/os/exec_unix.go
new file mode 100644
index 000000000..1b1e3350b
--- /dev/null
+++ b/src/os/exec_unix.go
@@ -0,0 +1,73 @@
+// 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.
+
+// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
+
+package os
+
+import (
+	"errors"
+	"runtime"
+	"syscall"
+	"time"
+)
+
+func (p *Process) wait() (ps *ProcessState, err error) {
+	if p.Pid == -1 {
+		return nil, syscall.EINVAL
+	}
+	var status syscall.WaitStatus
+	var rusage syscall.Rusage
+	pid1, e := syscall.Wait4(p.Pid, &status, 0, &rusage)
+	if e != nil {
+		return nil, NewSyscallError("wait", e)
+	}
+	if pid1 != 0 {
+		p.setDone()
+	}
+	ps = &ProcessState{
+		pid:    pid1,
+		status: status,
+		rusage: &rusage,
+	}
+	return ps, nil
+}
+
+func (p *Process) signal(sig Signal) error {
+	if p.done() {
+		return errors.New("os: process already finished")
+	}
+	if p.Pid == -1 {
+		return errors.New("os: process already released")
+	}
+	s, ok := sig.(syscall.Signal)
+	if !ok {
+		return errors.New("os: unsupported signal type")
+	}
+	if e := syscall.Kill(p.Pid, s); e != nil {
+		return e
+	}
+	return nil
+}
+
+func (p *Process) release() error {
+	// NOOP for unix.
+	p.Pid = -1
+	// no need for a finalizer anymore
+	runtime.SetFinalizer(p, nil)
+	return nil
+}
+
+func findProcess(pid int) (p *Process, err error) {
+	// NOOP for unix.
+	return newProcess(pid, 0), nil
+}
+
+func (p *ProcessState) userTime() time.Duration {
+	return time.Duration(p.rusage.Utime.Nano()) * time.Nanosecond
+}
+
+func (p *ProcessState) systemTime() time.Duration {
+	return time.Duration(p.rusage.Stime.Nano()) * time.Nanosecond
+}
diff --git a/src/os/exec_windows.go b/src/os/exec_windows.go
new file mode 100644
index 000000000..c4f3d4f85
--- /dev/null
+++ b/src/os/exec_windows.go
@@ -0,0 +1,115 @@
+// 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 (
+	"errors"
+	"runtime"
+	"syscall"
+	"time"
+	"unsafe"
+)
+
+func (p *Process) wait() (ps *ProcessState, err error) {
+	s, e := syscall.WaitForSingleObject(syscall.Handle(p.handle), syscall.INFINITE)
+	switch s {
+	case syscall.WAIT_OBJECT_0:
+		break
+	case syscall.WAIT_FAILED:
+		return nil, NewSyscallError("WaitForSingleObject", e)
+	default:
+		return nil, errors.New("os: unexpected result from WaitForSingleObject")
+	}
+	var ec uint32
+	e = syscall.GetExitCodeProcess(syscall.Handle(p.handle), &ec)
+	if e != nil {
+		return nil, NewSyscallError("GetExitCodeProcess", e)
+	}
+	var u syscall.Rusage
+	e = syscall.GetProcessTimes(syscall.Handle(p.handle), &u.CreationTime, &u.ExitTime, &u.KernelTime, &u.UserTime)
+	if e != nil {
+		return nil, NewSyscallError("GetProcessTimes", e)
+	}
+	p.setDone()
+	// NOTE(brainman): It seems that sometimes process is not dead
+	// when WaitForSingleObject returns. But we do not know any
+	// other way to wait for it. Sleeping for a while seems to do
+	// the trick sometimes. So we will sleep and smell the roses.
+	defer time.Sleep(5 * time.Millisecond)
+	defer p.Release()
+	return &ProcessState{p.Pid, syscall.WaitStatus{ExitCode: ec}, &u}, nil
+}
+
+func terminateProcess(pid, exitcode int) error {
+	h, e := syscall.OpenProcess(syscall.PROCESS_TERMINATE, false, uint32(pid))
+	if e != nil {
+		return NewSyscallError("OpenProcess", e)
+	}
+	defer syscall.CloseHandle(h)
+	e = syscall.TerminateProcess(h, uint32(exitcode))
+	return NewSyscallError("TerminateProcess", e)
+}
+
+func (p *Process) signal(sig Signal) error {
+	if p.done() {
+		return errors.New("os: process already finished")
+	}
+	if sig == Kill {
+		return terminateProcess(p.Pid, 1)
+	}
+	// TODO(rsc): Handle Interrupt too?
+	return syscall.Errno(syscall.EWINDOWS)
+}
+
+func (p *Process) release() error {
+	if p.handle == uintptr(syscall.InvalidHandle) {
+		return syscall.EINVAL
+	}
+	e := syscall.CloseHandle(syscall.Handle(p.handle))
+	if e != nil {
+		return NewSyscallError("CloseHandle", e)
+	}
+	p.handle = uintptr(syscall.InvalidHandle)
+	// no need for a finalizer anymore
+	runtime.SetFinalizer(p, nil)
+	return nil
+}
+
+func findProcess(pid int) (p *Process, err error) {
+	const da = syscall.STANDARD_RIGHTS_READ |
+		syscall.PROCESS_QUERY_INFORMATION | syscall.SYNCHRONIZE
+	h, e := syscall.OpenProcess(da, false, uint32(pid))
+	if e != nil {
+		return nil, NewSyscallError("OpenProcess", e)
+	}
+	return newProcess(pid, uintptr(h)), nil
+}
+
+func init() {
+	var argc int32
+	cmd := syscall.GetCommandLine()
+	argv, e := syscall.CommandLineToArgv(cmd, &argc)
+	if e != nil {
+		return
+	}
+	defer syscall.LocalFree(syscall.Handle(uintptr(unsafe.Pointer(argv))))
+	Args = make([]string, argc)
+	for i, v := range (*argv)[:argc] {
+		Args[i] = string(syscall.UTF16ToString((*v)[:]))
+	}
+}
+
+func ftToDuration(ft *syscall.Filetime) time.Duration {
+	n := int64(ft.HighDateTime)<<32 + int64(ft.LowDateTime) // in 100-nanosecond intervals
+	return time.Duration(n*100) * time.Nanosecond
+}
+
+func (p *ProcessState) userTime() time.Duration {
+	return ftToDuration(&p.rusage.UserTime)
+}
+
+func (p *ProcessState) systemTime() time.Duration {
+	return ftToDuration(&p.rusage.KernelTime)
+}
diff --git a/src/os/export_test.go b/src/os/export_test.go
new file mode 100644
index 000000000..9fa7936ae
--- /dev/null
+++ b/src/os/export_test.go
@@ -0,0 +1,10 @@
+// Copyright 2011 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
+
+// Export for testing.
+
+var Atime = atime
+var LstatP = &lstat
diff --git a/src/os/file.go b/src/os/file.go
new file mode 100644
index 000000000..b4a745801
--- /dev/null
+++ b/src/os/file.go
@@ -0,0 +1,257 @@
+// 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 provides a platform-independent interface to operating system
+// functionality. The design is Unix-like, although the error handling is
+// Go-like; failing calls return values of type error rather than error numbers.
+// Often, more information is available within the error. For example,
+// if a call that takes a file name fails, such as Open or Stat, the error
+// will include the failing file name when printed and will be of type
+// *PathError, which may be unpacked for more information.
+//
+// The os interface is intended to be uniform across all operating systems.
+// Features not generally available appear in the system-specific package syscall.
+//
+// Here is a simple example, opening a file and reading some of it.
+//
+//	file, err := os.Open("file.go") // For read access.
+//	if err != nil {
+//		log.Fatal(err)
+//	}
+//
+// If the open fails, the error string will be self-explanatory, like
+//
+//	open file.go: no such file or directory
+//
+// The file's data can then be read into a slice of bytes. Read and
+// Write take their byte counts from the length of the argument slice.
+//
+//	data := make([]byte, 100)
+//	count, err := file.Read(data)
+//	if err != nil {
+//		log.Fatal(err)
+//	}
+//	fmt.Printf("read %d bytes: %q\n", count, data[:count])
+//
+package os
+
+import (
+	"io"
+	"syscall"
+)
+
+// Name returns the name of the file as presented to Open.
+func (f *File) Name() string { return f.name }
+
+// Stdin, Stdout, and Stderr are open Files pointing to the standard input,
+// standard output, and standard error file descriptors.
+var (
+	Stdin  = NewFile(uintptr(syscall.Stdin), "/dev/stdin")
+	Stdout = NewFile(uintptr(syscall.Stdout), "/dev/stdout")
+	Stderr = NewFile(uintptr(syscall.Stderr), "/dev/stderr")
+)
+
+// Flags to Open wrapping those of the underlying system. Not all flags
+// may be implemented on a given system.
+const (
+	O_RDONLY int = syscall.O_RDONLY // open the file read-only.
+	O_WRONLY int = syscall.O_WRONLY // open the file write-only.
+	O_RDWR   int = syscall.O_RDWR   // open the file read-write.
+	O_APPEND int = syscall.O_APPEND // append data to the file when writing.
+	O_CREATE int = syscall.O_CREAT  // create a new file if none exists.
+	O_EXCL   int = syscall.O_EXCL   // used with O_CREATE, file must not exist
+	O_SYNC   int = syscall.O_SYNC   // open for synchronous I/O.
+	O_TRUNC  int = syscall.O_TRUNC  // if possible, truncate file when opened.
+)
+
+// Seek whence values.
+const (
+	SEEK_SET int = 0 // seek relative to the origin of the file
+	SEEK_CUR int = 1 // seek relative to the current offset
+	SEEK_END int = 2 // seek relative to the end
+)
+
+// LinkError records an error during a link or symlink or rename
+// system call and the paths that caused it.
+type LinkError struct {
+	Op  string
+	Old string
+	New string
+	Err error
+}
+
+func (e *LinkError) Error() string {
+	return e.Op + " " + e.Old + " " + e.New + ": " + e.Err.Error()
+}
+
+// Read reads up to len(b) bytes from the File.
+// It returns the number of bytes read and an error, if any.
+// EOF is signaled by a zero count with err set to io.EOF.
+func (f *File) Read(b []byte) (n int, err error) {
+	if f == nil {
+		return 0, ErrInvalid
+	}
+	n, e := f.read(b)
+	if n < 0 {
+		n = 0
+	}
+	if n == 0 && len(b) > 0 && e == nil {
+		return 0, io.EOF
+	}
+	if e != nil {
+		err = &PathError{"read", f.name, e}
+	}
+	return n, err
+}
+
+// ReadAt reads len(b) bytes from the File starting at byte offset off.
+// It returns the number of bytes read and the error, if any.
+// ReadAt always returns a non-nil error when n < len(b).
+// At end of file, that error is io.EOF.
+func (f *File) ReadAt(b []byte, off int64) (n int, err error) {
+	if f == nil {
+		return 0, ErrInvalid
+	}
+	for len(b) > 0 {
+		m, e := f.pread(b, off)
+		if m == 0 && e == nil {
+			return n, io.EOF
+		}
+		if e != nil {
+			err = &PathError{"read", f.name, e}
+			break
+		}
+		n += m
+		b = b[m:]
+		off += int64(m)
+	}
+	return
+}
+
+// Write writes len(b) bytes to the File.
+// It returns the number of bytes written and an error, if any.
+// Write returns a non-nil error when n != len(b).
+func (f *File) Write(b []byte) (n int, err error) {
+	if f == nil {
+		return 0, ErrInvalid
+	}
+	n, e := f.write(b)
+	if n < 0 {
+		n = 0
+	}
+	if n != len(b) {
+		err = io.ErrShortWrite
+	}
+
+	epipecheck(f, e)
+
+	if e != nil {
+		err = &PathError{"write", f.name, e}
+	}
+	return n, err
+}
+
+// WriteAt writes len(b) bytes to the File starting at byte offset off.
+// It returns the number of bytes written and an error, if any.
+// WriteAt returns a non-nil error when n != len(b).
+func (f *File) WriteAt(b []byte, off int64) (n int, err error) {
+	if f == nil {
+		return 0, ErrInvalid
+	}
+	for len(b) > 0 {
+		m, e := f.pwrite(b, off)
+		if e != nil {
+			err = &PathError{"write", f.name, e}
+			break
+		}
+		n += m
+		b = b[m:]
+		off += int64(m)
+	}
+	return
+}
+
+// Seek sets the offset for the next Read or Write on file to offset, interpreted
+// according to whence: 0 means relative to the origin of the file, 1 means
+// relative to the current offset, and 2 means relative to the end.
+// It returns the new offset and an error, if any.
+func (f *File) Seek(offset int64, whence int) (ret int64, err error) {
+	if f == nil {
+		return 0, ErrInvalid
+	}
+	r, e := f.seek(offset, whence)
+	if e == nil && f.dirinfo != nil && r != 0 {
+		e = syscall.EISDIR
+	}
+	if e != nil {
+		return 0, &PathError{"seek", f.name, e}
+	}
+	return r, nil
+}
+
+// WriteString is like Write, but writes the contents of string s rather than
+// a slice of bytes.
+func (f *File) WriteString(s string) (ret int, err error) {
+	if f == nil {
+		return 0, ErrInvalid
+	}
+	return f.Write([]byte(s))
+}
+
+// Mkdir creates a new directory with the specified name and permission bits.
+// If there is an error, it will be of type *PathError.
+func Mkdir(name string, perm FileMode) error {
+	e := syscall.Mkdir(name, syscallMode(perm))
+	if e != nil {
+		return &PathError{"mkdir", name, e}
+	}
+	return nil
+}
+
+// Chdir changes the current working directory to the named directory.
+// If there is an error, it will be of type *PathError.
+func Chdir(dir string) error {
+	if e := syscall.Chdir(dir); e != nil {
+		return &PathError{"chdir", dir, e}
+	}
+	return nil
+}
+
+// Chdir changes the current working directory to the file,
+// which must be a directory.
+// If there is an error, it will be of type *PathError.
+func (f *File) Chdir() error {
+	if f == nil {
+		return ErrInvalid
+	}
+	if e := syscall.Fchdir(f.fd); e != nil {
+		return &PathError{"chdir", f.name, e}
+	}
+	return nil
+}
+
+// Open opens the named file for reading.  If successful, methods on
+// the returned file can be used for reading; the associated file
+// descriptor has mode O_RDONLY.
+// If there is an error, it will be of type *PathError.
+func Open(name string) (file *File, err error) {
+	return OpenFile(name, O_RDONLY, 0)
+}
+
+// Create creates the named file mode 0666 (before umask), truncating
+// it if it already exists.  If successful, methods on the returned
+// File can be used for I/O; the associated file descriptor has mode
+// O_RDWR.
+// If there is an error, it will be of type *PathError.
+func Create(name string) (file *File, err error) {
+	return OpenFile(name, O_RDWR|O_CREATE|O_TRUNC, 0666)
+}
+
+// lstat is overridden in tests.
+var lstat = Lstat
+
+// Rename renames (moves) a file. OS-specific restrictions might apply.
+func Rename(oldpath, newpath string) error {
+	return rename(oldpath, newpath)
+}
diff --git a/src/os/file_plan9.go b/src/os/file_plan9.go
new file mode 100644
index 000000000..a804b8197
--- /dev/null
+++ b/src/os/file_plan9.go
@@ -0,0 +1,468 @@
+// Copyright 2011 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"
+	"syscall"
+	"time"
+)
+
+// File represents an open file descriptor.
+type File struct {
+	*file
+}
+
+// file is the real representation of *File.
+// The extra level of indirection ensures that no clients of os
+// can overwrite this data, which could cause the finalizer
+// to close the wrong file descriptor.
+type file struct {
+	fd      int
+	name    string
+	dirinfo *dirInfo // nil unless directory being read
+}
+
+// Fd returns the integer Unix file descriptor referencing the open file.
+func (f *File) Fd() uintptr {
+	if f == nil {
+		return ^(uintptr(0))
+	}
+	return uintptr(f.fd)
+}
+
+// NewFile returns a new File with the given file descriptor and name.
+func NewFile(fd uintptr, name string) *File {
+	fdi := int(fd)
+	if fdi < 0 {
+		return nil
+	}
+	f := &File{&file{fd: fdi, name: name}}
+	runtime.SetFinalizer(f.file, (*file).close)
+	return f
+}
+
+// Auxiliary information if the File describes a directory
+type dirInfo struct {
+	buf  [syscall.STATMAX]byte // buffer for directory I/O
+	nbuf int                   // length of buf; return value from Read
+	bufp int                   // location of next record in buf.
+}
+
+func epipecheck(file *File, e error) {
+}
+
+// DevNull is the name of the operating system's ``null device.''
+// On Unix-like systems, it is "/dev/null"; on Windows, "NUL".
+const DevNull = "/dev/null"
+
+// syscallMode returns the syscall-specific mode bits from Go's portable mode bits.
+func syscallMode(i FileMode) (o uint32) {
+	o |= uint32(i.Perm())
+	if i&ModeAppend != 0 {
+		o |= syscall.DMAPPEND
+	}
+	if i&ModeExclusive != 0 {
+		o |= syscall.DMEXCL
+	}
+	if i&ModeTemporary != 0 {
+		o |= syscall.DMTMP
+	}
+	return
+}
+
+// OpenFile is the generalized open call; most users will use Open
+// or Create instead.  It opens the named file with specified flag
+// (O_RDONLY etc.) and perm, (0666 etc.) if applicable.  If successful,
+// methods on the returned File can be used for I/O.
+// If there is an error, it will be of type *PathError.
+func OpenFile(name string, flag int, perm FileMode) (file *File, err error) {
+	var (
+		fd     int
+		e      error
+		create bool
+		excl   bool
+		trunc  bool
+		append bool
+	)
+
+	if flag&O_CREATE == O_CREATE {
+		flag = flag & ^O_CREATE
+		create = true
+	}
+	if flag&O_EXCL == O_EXCL {
+		excl = true
+	}
+	if flag&O_TRUNC == O_TRUNC {
+		trunc = true
+	}
+	// O_APPEND is emulated on Plan 9
+	if flag&O_APPEND == O_APPEND {
+		flag = flag &^ O_APPEND
+		append = true
+	}
+
+	if (create && trunc) || excl {
+		fd, e = syscall.Create(name, flag, syscallMode(perm))
+	} else {
+		fd, e = syscall.Open(name, flag)
+		if e != nil && create {
+			var e1 error
+			fd, e1 = syscall.Create(name, flag, syscallMode(perm))
+			if e1 == nil {
+				e = nil
+			}
+		}
+	}
+
+	if e != nil {
+		return nil, &PathError{"open", name, e}
+	}
+
+	if append {
+		if _, e = syscall.Seek(fd, 0, SEEK_END); e != nil {
+			return nil, &PathError{"seek", name, e}
+		}
+	}
+
+	return NewFile(uintptr(fd), name), nil
+}
+
+// Close closes the File, rendering it unusable for I/O.
+// It returns an error, if any.
+func (f *File) Close() error {
+	if f == nil {
+		return ErrInvalid
+	}
+	return f.file.close()
+}
+
+func (file *file) close() error {
+	if file == nil || file.fd < 0 {
+		return ErrInvalid
+	}
+	var err error
+	syscall.ForkLock.RLock()
+	if e := syscall.Close(file.fd); e != nil {
+		err = &PathError{"close", file.name, e}
+	}
+	syscall.ForkLock.RUnlock()
+	file.fd = -1 // so it can't be closed again
+
+	// no need for a finalizer anymore
+	runtime.SetFinalizer(file, nil)
+	return err
+}
+
+// Stat returns the FileInfo structure describing file.
+// If there is an error, it will be of type *PathError.
+func (f *File) Stat() (fi FileInfo, err error) {
+	if f == nil {
+		return nil, ErrInvalid
+	}
+	d, err := dirstat(f)
+	if err != nil {
+		return nil, err
+	}
+	return fileInfoFromStat(d), nil
+}
+
+// Truncate changes the size of the file.
+// It does not change the I/O offset.
+// If there is an error, it will be of type *PathError.
+func (f *File) Truncate(size int64) error {
+	if f == nil {
+		return ErrInvalid
+	}
+
+	var d syscall.Dir
+	d.Null()
+	d.Length = size
+
+	var buf [syscall.STATFIXLEN]byte
+	n, err := d.Marshal(buf[:])
+	if err != nil {
+		return &PathError{"truncate", f.name, err}
+	}
+	if err = syscall.Fwstat(f.fd, buf[:n]); err != nil {
+		return &PathError{"truncate", f.name, err}
+	}
+	return nil
+}
+
+const chmodMask = uint32(syscall.DMAPPEND | syscall.DMEXCL | syscall.DMTMP | ModePerm)
+
+// Chmod changes the mode of the file to mode.
+// If there is an error, it will be of type *PathError.
+func (f *File) Chmod(mode FileMode) error {
+	if f == nil {
+		return ErrInvalid
+	}
+	var d syscall.Dir
+
+	odir, e := dirstat(f)
+	if e != nil {
+		return &PathError{"chmod", f.name, e}
+	}
+	d.Null()
+	d.Mode = odir.Mode&^chmodMask | syscallMode(mode)&chmodMask
+
+	var buf [syscall.STATFIXLEN]byte
+	n, err := d.Marshal(buf[:])
+	if err != nil {
+		return &PathError{"chmod", f.name, err}
+	}
+	if err = syscall.Fwstat(f.fd, buf[:n]); err != nil {
+		return &PathError{"chmod", f.name, err}
+	}
+	return nil
+}
+
+// Sync commits the current contents of the file to stable storage.
+// Typically, this means flushing the file system's in-memory copy
+// of recently written data to disk.
+func (f *File) Sync() (err error) {
+	if f == nil {
+		return ErrInvalid
+	}
+	var d syscall.Dir
+	d.Null()
+
+	var buf [syscall.STATFIXLEN]byte
+	n, err := d.Marshal(buf[:])
+	if err != nil {
+		return NewSyscallError("fsync", err)
+	}
+	if err = syscall.Fwstat(f.fd, buf[:n]); err != nil {
+		return NewSyscallError("fsync", err)
+	}
+	return nil
+}
+
+// read reads up to len(b) bytes from the File.
+// It returns the number of bytes read and an error, if any.
+func (f *File) read(b []byte) (n int, err error) {
+	return syscall.Read(f.fd, b)
+}
+
+// pread reads len(b) bytes from the File starting at byte offset off.
+// It returns the number of bytes read and the error, if any.
+// EOF is signaled by a zero count with err set to nil.
+func (f *File) pread(b []byte, off int64) (n int, err error) {
+	return syscall.Pread(f.fd, b, off)
+}
+
+// write writes len(b) bytes to the File.
+// It returns the number of bytes written and an error, if any.
+// Since Plan 9 preserves message boundaries, never allow
+// a zero-byte write.
+func (f *File) write(b []byte) (n int, err error) {
+	if len(b) == 0 {
+		return 0, nil
+	}
+	return syscall.Write(f.fd, b)
+}
+
+// pwrite writes len(b) bytes to the File starting at byte offset off.
+// It returns the number of bytes written and an error, if any.
+// Since Plan 9 preserves message boundaries, never allow
+// a zero-byte write.
+func (f *File) pwrite(b []byte, off int64) (n int, err error) {
+	if len(b) == 0 {
+		return 0, nil
+	}
+	return syscall.Pwrite(f.fd, b, off)
+}
+
+// seek sets the offset for the next Read or Write on file to offset, interpreted
+// according to whence: 0 means relative to the origin of the file, 1 means
+// relative to the current offset, and 2 means relative to the end.
+// It returns the new offset and an error, if any.
+func (f *File) seek(offset int64, whence int) (ret int64, err error) {
+	return syscall.Seek(f.fd, offset, whence)
+}
+
+// Truncate changes the size of the named file.
+// If the file is a symbolic link, it changes the size of the link's target.
+// If there is an error, it will be of type *PathError.
+func Truncate(name string, size int64) error {
+	var d syscall.Dir
+
+	d.Null()
+	d.Length = size
+
+	var buf [syscall.STATFIXLEN]byte
+	n, err := d.Marshal(buf[:])
+	if err != nil {
+		return &PathError{"truncate", name, err}
+	}
+	if err = syscall.Wstat(name, buf[:n]); err != nil {
+		return &PathError{"truncate", name, err}
+	}
+	return nil
+}
+
+// Remove removes the named file or directory.
+// If there is an error, it will be of type *PathError.
+func Remove(name string) error {
+	if e := syscall.Remove(name); e != nil {
+		return &PathError{"remove", name, e}
+	}
+	return nil
+}
+
+// HasPrefix from the strings package.
+func hasPrefix(s, prefix string) bool {
+	return len(s) >= len(prefix) && s[0:len(prefix)] == prefix
+}
+
+// Variant of LastIndex from the strings package.
+func lastIndex(s string, sep byte) int {
+	for i := len(s) - 1; i >= 0; i-- {
+		if s[i] == sep {
+			return i
+		}
+	}
+	return -1
+}
+
+func rename(oldname, newname string) error {
+	dirname := oldname[:lastIndex(oldname, '/')+1]
+	if hasPrefix(newname, dirname) {
+		newname = newname[len(dirname):]
+	} else {
+		return &LinkError{"rename", oldname, newname, ErrInvalid}
+	}
+
+	// If newname still contains slashes after removing the oldname
+	// prefix, the rename is cross-directory and must be rejected.
+	// This case is caught by d.Marshal below.
+
+	var d syscall.Dir
+
+	d.Null()
+	d.Name = newname
+
+	buf := make([]byte, syscall.STATFIXLEN+len(d.Name))
+	n, err := d.Marshal(buf[:])
+	if err != nil {
+		return &LinkError{"rename", oldname, newname, err}
+	}
+	if err = syscall.Wstat(oldname, buf[:n]); err != nil {
+		return &LinkError{"rename", oldname, newname, err}
+	}
+	return nil
+}
+
+// Chmod changes the mode of the named file to mode.
+// If the file is a symbolic link, it changes the mode of the link's target.
+// If there is an error, it will be of type *PathError.
+func Chmod(name string, mode FileMode) error {
+	var d syscall.Dir
+
+	odir, e := dirstat(name)
+	if e != nil {
+		return &PathError{"chmod", name, e}
+	}
+	d.Null()
+	d.Mode = odir.Mode&^chmodMask | syscallMode(mode)&chmodMask
+
+	var buf [syscall.STATFIXLEN]byte
+	n, err := d.Marshal(buf[:])
+	if err != nil {
+		return &PathError{"chmod", name, err}
+	}
+	if err = syscall.Wstat(name, buf[:n]); err != nil {
+		return &PathError{"chmod", name, err}
+	}
+	return nil
+}
+
+// Chtimes changes the access and modification times of the named
+// file, similar to the Unix utime() or utimes() functions.
+//
+// The underlying filesystem may truncate or round the values to a
+// less precise time unit.
+// If there is an error, it will be of type *PathError.
+func Chtimes(name string, atime time.Time, mtime time.Time) error {
+	var d syscall.Dir
+
+	d.Null()
+	d.Atime = uint32(atime.Unix())
+	d.Mtime = uint32(mtime.Unix())
+
+	var buf [syscall.STATFIXLEN]byte
+	n, err := d.Marshal(buf[:])
+	if err != nil {
+		return &PathError{"chtimes", name, err}
+	}
+	if err = syscall.Wstat(name, buf[:n]); err != nil {
+		return &PathError{"chtimes", name, err}
+	}
+	return nil
+}
+
+// Pipe returns a connected pair of Files; reads from r return bytes
+// written to w. It returns the files and an error, if any.
+func Pipe() (r *File, w *File, err error) {
+	var p [2]int
+
+	syscall.ForkLock.RLock()
+	if e := syscall.Pipe(p[0:]); e != nil {
+		syscall.ForkLock.RUnlock()
+		return nil, nil, NewSyscallError("pipe", e)
+	}
+	syscall.ForkLock.RUnlock()
+
+	return NewFile(uintptr(p[0]), "|0"), NewFile(uintptr(p[1]), "|1"), nil
+}
+
+// not supported on Plan 9
+
+// Link creates newname as a hard link to the oldname file.
+// If there is an error, it will be of type *LinkError.
+func Link(oldname, newname string) error {
+	return &LinkError{"link", oldname, newname, syscall.EPLAN9}
+}
+
+// Symlink creates newname as a symbolic link to oldname.
+// If there is an error, it will be of type *LinkError.
+func Symlink(oldname, newname string) error {
+	return &LinkError{"symlink", oldname, newname, syscall.EPLAN9}
+}
+
+// Readlink returns the destination of the named symbolic link.
+// If there is an error, it will be of type *PathError.
+func Readlink(name string) (string, error) {
+	return "", &PathError{"readlink", name, syscall.EPLAN9}
+}
+
+// Chown changes the numeric uid and gid of the named file.
+// If the file is a symbolic link, it changes the uid and gid of the link's target.
+// If there is an error, it will be of type *PathError.
+func Chown(name string, uid, gid int) error {
+	return &PathError{"chown", name, syscall.EPLAN9}
+}
+
+// Lchown changes the numeric uid and gid of the named file.
+// If the file is a symbolic link, it changes the uid and gid of the link itself.
+// If there is an error, it will be of type *PathError.
+func Lchown(name string, uid, gid int) error {
+	return &PathError{"lchown", name, syscall.EPLAN9}
+}
+
+// Chown changes the numeric uid and gid of the named file.
+// If there is an error, it will be of type *PathError.
+func (f *File) Chown(uid, gid int) error {
+	if f == nil {
+		return ErrInvalid
+	}
+	return &PathError{"chown", f.name, syscall.EPLAN9}
+}
+
+// TempDir returns the default directory to use for temporary files.
+func TempDir() string {
+	return "/tmp"
+}
diff --git a/src/os/file_posix.go b/src/os/file_posix.go
new file mode 100644
index 000000000..9cff7e5bc
--- /dev/null
+++ b/src/os/file_posix.go
@@ -0,0 +1,149 @@
+// 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.
+
+// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris windows
+
+package os
+
+import (
+	"syscall"
+	"time"
+)
+
+func sigpipe() // implemented in package runtime
+
+// Readlink returns the destination of the named symbolic link.
+// If there is an error, it will be of type *PathError.
+func Readlink(name string) (string, error) {
+	for len := 128; ; len *= 2 {
+		b := make([]byte, len)
+		n, e := syscall.Readlink(name, b)
+		if e != nil {
+			return "", &PathError{"readlink", name, e}
+		}
+		if n < len {
+			return string(b[0:n]), nil
+		}
+	}
+}
+
+func rename(oldname, newname string) error {
+	e := syscall.Rename(oldname, newname)
+	if e != nil {
+		return &LinkError{"rename", oldname, newname, e}
+	}
+	return nil
+}
+
+// syscallMode returns the syscall-specific mode bits from Go's portable mode bits.
+func syscallMode(i FileMode) (o uint32) {
+	o |= uint32(i.Perm())
+	if i&ModeSetuid != 0 {
+		o |= syscall.S_ISUID
+	}
+	if i&ModeSetgid != 0 {
+		o |= syscall.S_ISGID
+	}
+	if i&ModeSticky != 0 {
+		o |= syscall.S_ISVTX
+	}
+	// No mapping for Go's ModeTemporary (plan9 only).
+	return
+}
+
+// Chmod changes the mode of the named file to mode.
+// If the file is a symbolic link, it changes the mode of the link's target.
+// If there is an error, it will be of type *PathError.
+func Chmod(name string, mode FileMode) error {
+	if e := syscall.Chmod(name, syscallMode(mode)); e != nil {
+		return &PathError{"chmod", name, e}
+	}
+	return nil
+}
+
+// Chmod changes the mode of the file to mode.
+// If there is an error, it will be of type *PathError.
+func (f *File) Chmod(mode FileMode) error {
+	if f == nil {
+		return ErrInvalid
+	}
+	if e := syscall.Fchmod(f.fd, syscallMode(mode)); e != nil {
+		return &PathError{"chmod", f.name, e}
+	}
+	return nil
+}
+
+// Chown changes the numeric uid and gid of the named file.
+// If the file is a symbolic link, it changes the uid and gid of the link's target.
+// If there is an error, it will be of type *PathError.
+func Chown(name string, uid, gid int) error {
+	if e := syscall.Chown(name, uid, gid); e != nil {
+		return &PathError{"chown", name, e}
+	}
+	return nil
+}
+
+// Lchown changes the numeric uid and gid of the named file.
+// If the file is a symbolic link, it changes the uid and gid of the link itself.
+// If there is an error, it will be of type *PathError.
+func Lchown(name string, uid, gid int) error {
+	if e := syscall.Lchown(name, uid, gid); e != nil {
+		return &PathError{"lchown", name, e}
+	}
+	return nil
+}
+
+// Chown changes the numeric uid and gid of the named file.
+// If there is an error, it will be of type *PathError.
+func (f *File) Chown(uid, gid int) error {
+	if f == nil {
+		return ErrInvalid
+	}
+	if e := syscall.Fchown(f.fd, uid, gid); e != nil {
+		return &PathError{"chown", f.name, e}
+	}
+	return nil
+}
+
+// Truncate changes the size of the file.
+// It does not change the I/O offset.
+// If there is an error, it will be of type *PathError.
+func (f *File) Truncate(size int64) error {
+	if f == nil {
+		return ErrInvalid
+	}
+	if e := syscall.Ftruncate(f.fd, size); e != nil {
+		return &PathError{"truncate", f.name, e}
+	}
+	return nil
+}
+
+// Sync commits the current contents of the file to stable storage.
+// Typically, this means flushing the file system's in-memory copy
+// of recently written data to disk.
+func (f *File) Sync() (err error) {
+	if f == nil {
+		return ErrInvalid
+	}
+	if e := syscall.Fsync(f.fd); e != nil {
+		return NewSyscallError("fsync", e)
+	}
+	return nil
+}
+
+// Chtimes changes the access and modification times of the named
+// file, similar to the Unix utime() or utimes() functions.
+//
+// The underlying filesystem may truncate or round the values to a
+// less precise time unit.
+// If there is an error, it will be of type *PathError.
+func Chtimes(name string, atime time.Time, mtime time.Time) error {
+	var utimes [2]syscall.Timespec
+	utimes[0] = syscall.NsecToTimespec(atime.UnixNano())
+	utimes[1] = syscall.NsecToTimespec(mtime.UnixNano())
+	if e := syscall.UtimesNano(name, utimes[0:]); e != nil {
+		return &PathError{"chtimes", name, e}
+	}
+	return nil
+}
diff --git a/src/os/file_unix.go b/src/os/file_unix.go
new file mode 100644
index 000000000..bba0d9c0f
--- /dev/null
+++ b/src/os/file_unix.go
@@ -0,0 +1,338 @@
+// 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.
+
+// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
+
+package os
+
+import (
+	"runtime"
+	"sync/atomic"
+	"syscall"
+)
+
+// File represents an open file descriptor.
+type File struct {
+	*file
+}
+
+// file is the real representation of *File.
+// The extra level of indirection ensures that no clients of os
+// can overwrite this data, which could cause the finalizer
+// to close the wrong file descriptor.
+type file struct {
+	fd      int
+	name    string
+	dirinfo *dirInfo // nil unless directory being read
+	nepipe  int32    // number of consecutive EPIPE in Write
+}
+
+// Fd returns the integer Unix file descriptor referencing the open file.
+func (f *File) Fd() uintptr {
+	if f == nil {
+		return ^(uintptr(0))
+	}
+	return uintptr(f.fd)
+}
+
+// NewFile returns a new File with the given file descriptor and name.
+func NewFile(fd uintptr, name string) *File {
+	fdi := int(fd)
+	if fdi < 0 {
+		return nil
+	}
+	f := &File{&file{fd: fdi, name: name}}
+	runtime.SetFinalizer(f.file, (*file).close)
+	return f
+}
+
+// Auxiliary information if the File describes a directory
+type dirInfo struct {
+	buf  []byte // buffer for directory I/O
+	nbuf int    // length of buf; return value from Getdirentries
+	bufp int    // location of next record in buf.
+}
+
+func epipecheck(file *File, e error) {
+	if e == syscall.EPIPE {
+		if atomic.AddInt32(&file.nepipe, 1) >= 10 {
+			sigpipe()
+		}
+	} else {
+		atomic.StoreInt32(&file.nepipe, 0)
+	}
+}
+
+// DevNull is the name of the operating system's ``null device.''
+// On Unix-like systems, it is "/dev/null"; on Windows, "NUL".
+const DevNull = "/dev/null"
+
+// OpenFile is the generalized open call; most users will use Open
+// or Create instead.  It opens the named file with specified flag
+// (O_RDONLY etc.) and perm, (0666 etc.) if applicable.  If successful,
+// methods on the returned File can be used for I/O.
+// If there is an error, it will be of type *PathError.
+func OpenFile(name string, flag int, perm FileMode) (file *File, err error) {
+	r, e := syscall.Open(name, flag|syscall.O_CLOEXEC, syscallMode(perm))
+	if e != nil {
+		return nil, &PathError{"open", name, e}
+	}
+
+	// There's a race here with fork/exec, which we are
+	// content to live with.  See ../syscall/exec_unix.go.
+	if !supportsCloseOnExec {
+		syscall.CloseOnExec(r)
+	}
+
+	return NewFile(uintptr(r), name), nil
+}
+
+// Close closes the File, rendering it unusable for I/O.
+// It returns an error, if any.
+func (f *File) Close() error {
+	if f == nil {
+		return ErrInvalid
+	}
+	return f.file.close()
+}
+
+func (file *file) close() error {
+	if file == nil || file.fd < 0 {
+		return syscall.EINVAL
+	}
+	var err error
+	if e := syscall.Close(file.fd); e != nil {
+		err = &PathError{"close", file.name, e}
+	}
+	file.fd = -1 // so it can't be closed again
+
+	// no need for a finalizer anymore
+	runtime.SetFinalizer(file, nil)
+	return err
+}
+
+// Stat returns the FileInfo structure describing file.
+// If there is an error, it will be of type *PathError.
+func (f *File) Stat() (fi FileInfo, err error) {
+	if f == nil {
+		return nil, ErrInvalid
+	}
+	var stat syscall.Stat_t
+	err = syscall.Fstat(f.fd, &stat)
+	if err != nil {
+		return nil, &PathError{"stat", f.name, err}
+	}
+	return fileInfoFromStat(&stat, f.name), nil
+}
+
+// Stat returns a FileInfo describing the named file.
+// If there is an error, it will be of type *PathError.
+func Stat(name string) (fi FileInfo, err error) {
+	var stat syscall.Stat_t
+	err = syscall.Stat(name, &stat)
+	if err != nil {
+		return nil, &PathError{"stat", name, err}
+	}
+	return fileInfoFromStat(&stat, name), nil
+}
+
+// Lstat returns a FileInfo describing the named file.
+// If the file is a symbolic link, the returned FileInfo
+// describes the symbolic link.  Lstat makes no attempt to follow the link.
+// If there is an error, it will be of type *PathError.
+func Lstat(name string) (fi FileInfo, err error) {
+	var stat syscall.Stat_t
+	err = syscall.Lstat(name, &stat)
+	if err != nil {
+		return nil, &PathError{"lstat", name, err}
+	}
+	return fileInfoFromStat(&stat, name), nil
+}
+
+func (f *File) readdir(n int) (fi []FileInfo, err error) {
+	dirname := f.name
+	if dirname == "" {
+		dirname = "."
+	}
+	names, err := f.Readdirnames(n)
+	fi = make([]FileInfo, 0, len(names))
+	for _, filename := range names {
+		fip, lerr := lstat(dirname + "/" + filename)
+		if IsNotExist(lerr) {
+			// File disappeared between readdir + stat.
+			// Just treat it as if it didn't exist.
+			continue
+		}
+		if lerr != nil {
+			return fi, lerr
+		}
+		fi = append(fi, fip)
+	}
+	return fi, err
+}
+
+// Darwin and FreeBSD can't read or write 2GB+ at a time,
+// even on 64-bit systems. See golang.org/issue/7812.
+// Use 1GB instead of, say, 2GB-1, to keep subsequent
+// reads aligned.
+const (
+	needsMaxRW = runtime.GOOS == "darwin" || runtime.GOOS == "freebsd"
+	maxRW      = 1 << 30
+)
+
+// read reads up to len(b) bytes from the File.
+// It returns the number of bytes read and an error, if any.
+func (f *File) read(b []byte) (n int, err error) {
+	if needsMaxRW && len(b) > maxRW {
+		b = b[:maxRW]
+	}
+	return syscall.Read(f.fd, b)
+}
+
+// pread reads len(b) bytes from the File starting at byte offset off.
+// It returns the number of bytes read and the error, if any.
+// EOF is signaled by a zero count with err set to nil.
+func (f *File) pread(b []byte, off int64) (n int, err error) {
+	if needsMaxRW && len(b) > maxRW {
+		b = b[:maxRW]
+	}
+	return syscall.Pread(f.fd, b, off)
+}
+
+// write writes len(b) bytes to the File.
+// It returns the number of bytes written and an error, if any.
+func (f *File) write(b []byte) (n int, err error) {
+	for {
+		bcap := b
+		if needsMaxRW && len(bcap) > maxRW {
+			bcap = bcap[:maxRW]
+		}
+		m, err := syscall.Write(f.fd, bcap)
+		n += m
+
+		// If the syscall wrote some data but not all (short write)
+		// or it returned EINTR, then assume it stopped early for
+		// reasons that are uninteresting to the caller, and try again.
+		if 0 < m && m < len(bcap) || err == syscall.EINTR {
+			b = b[m:]
+			continue
+		}
+
+		if needsMaxRW && len(bcap) != len(b) && err == nil {
+			b = b[m:]
+			continue
+		}
+
+		return n, err
+	}
+}
+
+// pwrite writes len(b) bytes to the File starting at byte offset off.
+// It returns the number of bytes written and an error, if any.
+func (f *File) pwrite(b []byte, off int64) (n int, err error) {
+	if needsMaxRW && len(b) > maxRW {
+		b = b[:maxRW]
+	}
+	return syscall.Pwrite(f.fd, b, off)
+}
+
+// seek sets the offset for the next Read or Write on file to offset, interpreted
+// according to whence: 0 means relative to the origin of the file, 1 means
+// relative to the current offset, and 2 means relative to the end.
+// It returns the new offset and an error, if any.
+func (f *File) seek(offset int64, whence int) (ret int64, err error) {
+	return syscall.Seek(f.fd, offset, whence)
+}
+
+// Truncate changes the size of the named file.
+// If the file is a symbolic link, it changes the size of the link's target.
+// If there is an error, it will be of type *PathError.
+func Truncate(name string, size int64) error {
+	if e := syscall.Truncate(name, size); e != nil {
+		return &PathError{"truncate", name, e}
+	}
+	return nil
+}
+
+// Remove removes the named file or directory.
+// If there is an error, it will be of type *PathError.
+func Remove(name string) error {
+	// System call interface forces us to know
+	// whether name is a file or directory.
+	// Try both: it is cheaper on average than
+	// doing a Stat plus the right one.
+	e := syscall.Unlink(name)
+	if e == nil {
+		return nil
+	}
+	e1 := syscall.Rmdir(name)
+	if e1 == nil {
+		return nil
+	}
+
+	// Both failed: figure out which error to return.
+	// OS X and Linux differ on whether unlink(dir)
+	// returns EISDIR, so can't use that.  However,
+	// both agree that rmdir(file) returns ENOTDIR,
+	// so we can use that to decide which error is real.
+	// Rmdir might also return ENOTDIR if given a bad
+	// file path, like /etc/passwd/foo, but in that case,
+	// both errors will be ENOTDIR, so it's okay to
+	// use the error from unlink.
+	if e1 != syscall.ENOTDIR {
+		e = e1
+	}
+	return &PathError{"remove", name, e}
+}
+
+// basename removes trailing slashes and the leading directory name from path name
+func basename(name string) string {
+	i := len(name) - 1
+	// Remove trailing slashes
+	for ; i > 0 && name[i] == '/'; i-- {
+		name = name[:i]
+	}
+	// Remove leading directory name
+	for i--; i >= 0; i-- {
+		if name[i] == '/' {
+			name = name[i+1:]
+			break
+		}
+	}
+
+	return name
+}
+
+// TempDir returns the default directory to use for temporary files.
+func TempDir() string {
+	dir := Getenv("TMPDIR")
+	if dir == "" {
+		if runtime.GOOS == "android" {
+			dir = "/data/local/tmp"
+		} else {
+			dir = "/tmp"
+		}
+	}
+	return dir
+}
+
+// Link creates newname as a hard link to the oldname file.
+// If there is an error, it will be of type *LinkError.
+func Link(oldname, newname string) error {
+	e := syscall.Link(oldname, newname)
+	if e != nil {
+		return &LinkError{"link", oldname, newname, e}
+	}
+	return nil
+}
+
+// Symlink creates newname as a symbolic link to oldname.
+// If there is an error, it will be of type *LinkError.
+func Symlink(oldname, newname string) error {
+	e := syscall.Symlink(oldname, newname)
+	if e != nil {
+		return &LinkError{"symlink", oldname, newname, e}
+	}
+	return nil
+}
diff --git a/src/os/file_windows.go b/src/os/file_windows.go
new file mode 100644
index 000000000..e78d4abf6
--- /dev/null
+++ b/src/os/file_windows.go
@@ -0,0 +1,595 @@
+// 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 (
+	"io"
+	"runtime"
+	"sync"
+	"syscall"
+	"unicode/utf16"
+	"unicode/utf8"
+	"unsafe"
+)
+
+// File represents an open file descriptor.
+type File struct {
+	*file
+}
+
+// file is the real representation of *File.
+// The extra level of indirection ensures that no clients of os
+// can overwrite this data, which could cause the finalizer
+// to close the wrong file descriptor.
+type file struct {
+	fd      syscall.Handle
+	name    string
+	dirinfo *dirInfo   // nil unless directory being read
+	l       sync.Mutex // used to implement windows pread/pwrite
+
+	// only for console io
+	isConsole bool
+	lastbits  []byte // first few bytes of the last incomplete rune in last write
+	readbuf   []rune // input console buffer
+}
+
+// Fd returns the Windows handle referencing the open file.
+func (file *File) Fd() uintptr {
+	if file == nil {
+		return uintptr(syscall.InvalidHandle)
+	}
+	return uintptr(file.fd)
+}
+
+// newFile returns a new File with the given file handle and name.
+// Unlike NewFile, it does not check that h is syscall.InvalidHandle.
+func newFile(h syscall.Handle, name string) *File {
+	f := &File{&file{fd: h, name: name}}
+	var m uint32
+	if syscall.GetConsoleMode(f.fd, &m) == nil {
+		f.isConsole = true
+	}
+	runtime.SetFinalizer(f.file, (*file).close)
+	return f
+}
+
+// NewFile returns a new File with the given file descriptor and name.
+func NewFile(fd uintptr, name string) *File {
+	h := syscall.Handle(fd)
+	if h == syscall.InvalidHandle {
+		return nil
+	}
+	return newFile(h, name)
+}
+
+// Auxiliary information if the File describes a directory
+type dirInfo struct {
+	data     syscall.Win32finddata
+	needdata bool
+	path     string
+	isempty  bool // set if FindFirstFile returns ERROR_FILE_NOT_FOUND
+}
+
+func epipecheck(file *File, e error) {
+}
+
+const DevNull = "NUL"
+
+func (f *file) isdir() bool { return f != nil && f.dirinfo != nil }
+
+func openFile(name string, flag int, perm FileMode) (file *File, err error) {
+	r, e := syscall.Open(name, flag|syscall.O_CLOEXEC, syscallMode(perm))
+	if e != nil {
+		return nil, e
+	}
+	return NewFile(uintptr(r), name), nil
+}
+
+func openDir(name string) (file *File, err error) {
+	maskp, e := syscall.UTF16PtrFromString(name + `\*`)
+	if e != nil {
+		return nil, e
+	}
+	d := new(dirInfo)
+	r, e := syscall.FindFirstFile(maskp, &d.data)
+	if e != nil {
+		// FindFirstFile returns ERROR_FILE_NOT_FOUND when
+		// no matching files can be found. Then, if directory
+		// exists, we should proceed.
+		if e != syscall.ERROR_FILE_NOT_FOUND {
+			return nil, e
+		}
+		var fa syscall.Win32FileAttributeData
+		namep, e := syscall.UTF16PtrFromString(name)
+		if e != nil {
+			return nil, e
+		}
+		e = syscall.GetFileAttributesEx(namep, syscall.GetFileExInfoStandard, (*byte)(unsafe.Pointer(&fa)))
+		if e != nil {
+			return nil, e
+		}
+		if fa.FileAttributes&syscall.FILE_ATTRIBUTE_DIRECTORY == 0 {
+			return nil, e
+		}
+		d.isempty = true
+	}
+	d.path = name
+	if !isAbs(d.path) {
+		d.path, e = syscall.FullPath(d.path)
+		if e != nil {
+			return nil, e
+		}
+	}
+	f := newFile(r, name)
+	f.dirinfo = d
+	return f, nil
+}
+
+// OpenFile is the generalized open call; most users will use Open
+// or Create instead.  It opens the named file with specified flag
+// (O_RDONLY etc.) and perm, (0666 etc.) if applicable.  If successful,
+// methods on the returned File can be used for I/O.
+// If there is an error, it will be of type *PathError.
+func OpenFile(name string, flag int, perm FileMode) (file *File, err error) {
+	if name == "" {
+		return nil, &PathError{"open", name, syscall.ENOENT}
+	}
+	r, errf := openFile(name, flag, perm)
+	if errf == nil {
+		return r, nil
+	}
+	r, errd := openDir(name)
+	if errd == nil {
+		if flag&O_WRONLY != 0 || flag&O_RDWR != 0 {
+			r.Close()
+			return nil, &PathError{"open", name, syscall.EISDIR}
+		}
+		return r, nil
+	}
+	return nil, &PathError{"open", name, errf}
+}
+
+// Close closes the File, rendering it unusable for I/O.
+// It returns an error, if any.
+func (file *File) Close() error {
+	if file == nil {
+		return ErrInvalid
+	}
+	return file.file.close()
+}
+
+func (file *file) close() error {
+	if file == nil {
+		return syscall.EINVAL
+	}
+	if file.isdir() && file.dirinfo.isempty {
+		// "special" empty directories
+		return nil
+	}
+	if file.fd == syscall.InvalidHandle {
+		return syscall.EINVAL
+	}
+	var e error
+	if file.isdir() {
+		e = syscall.FindClose(syscall.Handle(file.fd))
+	} else {
+		e = syscall.CloseHandle(syscall.Handle(file.fd))
+	}
+	var err error
+	if e != nil {
+		err = &PathError{"close", file.name, e}
+	}
+	file.fd = syscall.InvalidHandle // so it can't be closed again
+
+	// no need for a finalizer anymore
+	runtime.SetFinalizer(file, nil)
+	return err
+}
+
+func (file *File) readdir(n int) (fi []FileInfo, err error) {
+	if file == nil {
+		return nil, syscall.EINVAL
+	}
+	if !file.isdir() {
+		return nil, &PathError{"Readdir", file.name, syscall.ENOTDIR}
+	}
+	if !file.dirinfo.isempty && file.fd == syscall.InvalidHandle {
+		return nil, syscall.EINVAL
+	}
+	wantAll := n <= 0
+	size := n
+	if wantAll {
+		n = -1
+		size = 100
+	}
+	fi = make([]FileInfo, 0, size) // Empty with room to grow.
+	d := &file.dirinfo.data
+	for n != 0 && !file.dirinfo.isempty {
+		if file.dirinfo.needdata {
+			e := syscall.FindNextFile(syscall.Handle(file.fd), d)
+			if e != nil {
+				if e == syscall.ERROR_NO_MORE_FILES {
+					break
+				} else {
+					err = &PathError{"FindNextFile", file.name, e}
+					if !wantAll {
+						fi = nil
+					}
+					return
+				}
+			}
+		}
+		file.dirinfo.needdata = true
+		name := string(syscall.UTF16ToString(d.FileName[0:]))
+		if name == "." || name == ".." { // Useless names
+			continue
+		}
+		f := &fileStat{
+			name: name,
+			sys: syscall.Win32FileAttributeData{
+				FileAttributes: d.FileAttributes,
+				CreationTime:   d.CreationTime,
+				LastAccessTime: d.LastAccessTime,
+				LastWriteTime:  d.LastWriteTime,
+				FileSizeHigh:   d.FileSizeHigh,
+				FileSizeLow:    d.FileSizeLow,
+			},
+			path: file.dirinfo.path + `\` + name,
+		}
+		n--
+		fi = append(fi, f)
+	}
+	if !wantAll && len(fi) == 0 {
+		return fi, io.EOF
+	}
+	return fi, nil
+}
+
+// readConsole reads utf16 characters from console File,
+// encodes them into utf8 and stores them in buffer b.
+// It returns the number of utf8 bytes read and an error, if any.
+func (f *File) readConsole(b []byte) (n int, err error) {
+	if len(b) == 0 {
+		return 0, nil
+	}
+	if len(f.readbuf) == 0 {
+		// syscall.ReadConsole seems to fail, if given large buffer.
+		// So limit the buffer to 16000 characters.
+		numBytes := len(b)
+		if numBytes > 16000 {
+			numBytes = 16000
+		}
+		// get more input data from os
+		wchars := make([]uint16, numBytes)
+		var p *uint16
+		if len(b) > 0 {
+			p = &wchars[0]
+		}
+		var nw uint32
+		err := syscall.ReadConsole(f.fd, p, uint32(len(wchars)), &nw, nil)
+		if err != nil {
+			return 0, err
+		}
+		f.readbuf = utf16.Decode(wchars[:nw])
+	}
+	for i, r := range f.readbuf {
+		if utf8.RuneLen(r) > len(b) {
+			f.readbuf = f.readbuf[i:]
+			return n, nil
+		}
+		nr := utf8.EncodeRune(b, r)
+		b = b[nr:]
+		n += nr
+	}
+	f.readbuf = nil
+	return n, nil
+}
+
+// read reads up to len(b) bytes from the File.
+// It returns the number of bytes read and an error, if any.
+func (f *File) read(b []byte) (n int, err error) {
+	f.l.Lock()
+	defer f.l.Unlock()
+	if f.isConsole {
+		return f.readConsole(b)
+	}
+	return syscall.Read(f.fd, b)
+}
+
+// pread reads len(b) bytes from the File starting at byte offset off.
+// It returns the number of bytes read and the error, if any.
+// EOF is signaled by a zero count with err set to 0.
+func (f *File) pread(b []byte, off int64) (n int, err error) {
+	f.l.Lock()
+	defer f.l.Unlock()
+	curoffset, e := syscall.Seek(f.fd, 0, 1)
+	if e != nil {
+		return 0, e
+	}
+	defer syscall.Seek(f.fd, curoffset, 0)
+	o := syscall.Overlapped{
+		OffsetHigh: uint32(off >> 32),
+		Offset:     uint32(off),
+	}
+	var done uint32
+	e = syscall.ReadFile(syscall.Handle(f.fd), b, &done, &o)
+	if e != nil {
+		if e == syscall.ERROR_HANDLE_EOF {
+			// end of file
+			return 0, nil
+		}
+		return 0, e
+	}
+	return int(done), nil
+}
+
+// writeConsole writes len(b) bytes to the console File.
+// It returns the number of bytes written and an error, if any.
+func (f *File) writeConsole(b []byte) (n int, err error) {
+	n = len(b)
+	runes := make([]rune, 0, 256)
+	if len(f.lastbits) > 0 {
+		b = append(f.lastbits, b...)
+		f.lastbits = nil
+
+	}
+	for len(b) >= utf8.UTFMax || utf8.FullRune(b) {
+		r, l := utf8.DecodeRune(b)
+		runes = append(runes, r)
+		b = b[l:]
+	}
+	if len(b) > 0 {
+		f.lastbits = make([]byte, len(b))
+		copy(f.lastbits, b)
+	}
+	// syscall.WriteConsole seems to fail, if given large buffer.
+	// So limit the buffer to 16000 characters. This number was
+	// discovered by experimenting with syscall.WriteConsole.
+	const maxWrite = 16000
+	for len(runes) > 0 {
+		m := len(runes)
+		if m > maxWrite {
+			m = maxWrite
+		}
+		chunk := runes[:m]
+		runes = runes[m:]
+		uint16s := utf16.Encode(chunk)
+		for len(uint16s) > 0 {
+			var written uint32
+			err = syscall.WriteConsole(f.fd, &uint16s[0], uint32(len(uint16s)), &written, nil)
+			if err != nil {
+				return 0, nil
+			}
+			uint16s = uint16s[written:]
+		}
+	}
+	return n, nil
+}
+
+// write writes len(b) bytes to the File.
+// It returns the number of bytes written and an error, if any.
+func (f *File) write(b []byte) (n int, err error) {
+	f.l.Lock()
+	defer f.l.Unlock()
+	if f.isConsole {
+		return f.writeConsole(b)
+	}
+	return syscall.Write(f.fd, b)
+}
+
+// pwrite writes len(b) bytes to the File starting at byte offset off.
+// It returns the number of bytes written and an error, if any.
+func (f *File) pwrite(b []byte, off int64) (n int, err error) {
+	f.l.Lock()
+	defer f.l.Unlock()
+	curoffset, e := syscall.Seek(f.fd, 0, 1)
+	if e != nil {
+		return 0, e
+	}
+	defer syscall.Seek(f.fd, curoffset, 0)
+	o := syscall.Overlapped{
+		OffsetHigh: uint32(off >> 32),
+		Offset:     uint32(off),
+	}
+	var done uint32
+	e = syscall.WriteFile(syscall.Handle(f.fd), b, &done, &o)
+	if e != nil {
+		return 0, e
+	}
+	return int(done), nil
+}
+
+// seek sets the offset for the next Read or Write on file to offset, interpreted
+// according to whence: 0 means relative to the origin of the file, 1 means
+// relative to the current offset, and 2 means relative to the end.
+// It returns the new offset and an error, if any.
+func (f *File) seek(offset int64, whence int) (ret int64, err error) {
+	f.l.Lock()
+	defer f.l.Unlock()
+	return syscall.Seek(f.fd, offset, whence)
+}
+
+// Truncate changes the size of the named file.
+// If the file is a symbolic link, it changes the size of the link's target.
+func Truncate(name string, size int64) error {
+	f, e := OpenFile(name, O_WRONLY|O_CREATE, 0666)
+	if e != nil {
+		return e
+	}
+	defer f.Close()
+	e1 := f.Truncate(size)
+	if e1 != nil {
+		return e1
+	}
+	return nil
+}
+
+// Remove removes the named file or directory.
+// If there is an error, it will be of type *PathError.
+func Remove(name string) error {
+	p, e := syscall.UTF16PtrFromString(name)
+	if e != nil {
+		return &PathError{"remove", name, e}
+	}
+
+	// Go file interface forces us to know whether
+	// name is a file or directory. Try both.
+	e = syscall.DeleteFile(p)
+	if e == nil {
+		return nil
+	}
+	e1 := syscall.RemoveDirectory(p)
+	if e1 == nil {
+		return nil
+	}
+
+	// Both failed: figure out which error to return.
+	if e1 != e {
+		a, e2 := syscall.GetFileAttributes(p)
+		if e2 != nil {
+			e = e2
+		} else {
+			if a&syscall.FILE_ATTRIBUTE_DIRECTORY != 0 {
+				e = e1
+			}
+		}
+	}
+	return &PathError{"remove", name, e}
+}
+
+// Pipe returns a connected pair of Files; reads from r return bytes written to w.
+// It returns the files and an error, if any.
+func Pipe() (r *File, w *File, err error) {
+	var p [2]syscall.Handle
+
+	// See ../syscall/exec.go for description of lock.
+	syscall.ForkLock.RLock()
+	e := syscall.Pipe(p[0:])
+	if e != nil {
+		syscall.ForkLock.RUnlock()
+		return nil, nil, NewSyscallError("pipe", e)
+	}
+	syscall.CloseOnExec(p[0])
+	syscall.CloseOnExec(p[1])
+	syscall.ForkLock.RUnlock()
+
+	return NewFile(uintptr(p[0]), "|0"), NewFile(uintptr(p[1]), "|1"), nil
+}
+
+// TempDir returns the default directory to use for temporary files.
+func TempDir() string {
+	const pathSep = '\\'
+	dirw := make([]uint16, syscall.MAX_PATH)
+	n, _ := syscall.GetTempPath(uint32(len(dirw)), &dirw[0])
+	if n > uint32(len(dirw)) {
+		dirw = make([]uint16, n)
+		n, _ = syscall.GetTempPath(uint32(len(dirw)), &dirw[0])
+		if n > uint32(len(dirw)) {
+			n = 0
+		}
+	}
+	if n > 0 && dirw[n-1] == pathSep {
+		n--
+	}
+	return string(utf16.Decode(dirw[0:n]))
+}
+
+// Link creates newname as a hard link to the oldname file.
+// If there is an error, it will be of type *LinkError.
+func Link(oldname, newname string) error {
+	n, err := syscall.UTF16PtrFromString(newname)
+	if err != nil {
+		return &LinkError{"link", oldname, newname, err}
+	}
+	o, err := syscall.UTF16PtrFromString(oldname)
+	if err != nil {
+		return &LinkError{"link", oldname, newname, err}
+	}
+
+	e := syscall.CreateHardLink(n, o, 0)
+	if e != nil {
+		return &LinkError{"link", oldname, newname, err}
+	}
+	return nil
+}
+
+// Symlink creates newname as a symbolic link to oldname.
+// If there is an error, it will be of type *LinkError.
+func Symlink(oldname, newname string) error {
+	// CreateSymbolicLink is not supported before Windows Vista
+	if syscall.LoadCreateSymbolicLink() != nil {
+		return &LinkError{"symlink", oldname, newname, syscall.EWINDOWS}
+	}
+
+	// '/' does not work in link's content
+	oldname = fromSlash(oldname)
+
+	// need the exact location of the oldname when its relative to determine if its a directory
+	destpath := oldname
+	if !isAbs(oldname) {
+		destpath = dirname(newname) + `\` + oldname
+	}
+
+	fi, err := Lstat(destpath)
+	isdir := err == nil && fi.IsDir()
+
+	n, err := syscall.UTF16PtrFromString(newname)
+	if err != nil {
+		return &LinkError{"symlink", oldname, newname, err}
+	}
+	o, err := syscall.UTF16PtrFromString(oldname)
+	if err != nil {
+		return &LinkError{"symlink", oldname, newname, err}
+	}
+
+	var flags uint32
+	if isdir {
+		flags |= syscall.SYMBOLIC_LINK_FLAG_DIRECTORY
+	}
+	err = syscall.CreateSymbolicLink(n, o, flags)
+	if err != nil {
+		return &LinkError{"symlink", oldname, newname, err}
+	}
+	return nil
+}
+
+func fromSlash(path string) string {
+	// Replace each '/' with '\\' if present
+	var pathbuf []byte
+	var lastSlash int
+	for i, b := range path {
+		if b == '/' {
+			if pathbuf == nil {
+				pathbuf = make([]byte, len(path))
+			}
+			copy(pathbuf[lastSlash:], path[lastSlash:i])
+			pathbuf[i] = '\\'
+			lastSlash = i + 1
+		}
+	}
+	if pathbuf == nil {
+		return path
+	}
+
+	copy(pathbuf[lastSlash:], path[lastSlash:])
+	return string(pathbuf)
+}
+
+func dirname(path string) string {
+	vol := volumeName(path)
+	i := len(path) - 1
+	for i >= len(vol) && !IsPathSeparator(path[i]) {
+		i--
+	}
+	dir := path[len(vol) : i+1]
+	last := len(dir) - 1
+	if last > 0 && IsPathSeparator(dir[last]) {
+		dir = dir[:last]
+	}
+	if dir == "" {
+		dir = "."
+	}
+	return vol + dir
+}
diff --git a/src/os/getwd.go b/src/os/getwd.go
new file mode 100644
index 000000000..d5da53b34
--- /dev/null
+++ b/src/os/getwd.go
@@ -0,0 +1,123 @@
+// 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
+}
+
+// useSyscallwd determines whether to use the return value of
+// syscall.Getwd based on its error.
+var useSyscallwd = func(error) bool { return true }
+
+// 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" {
+		return syscall.Getwd()
+	}
+
+	// Clumsy but widespread kludge:
+	// if $PWD is set and matches ".", use it.
+	dot, err := Stat(".")
+	if err != nil {
+		return "", err
+	}
+	dir = Getenv("PWD")
+	if len(dir) > 0 && dir[0] == '/' {
+		d, err := Stat(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 {
+		s, e := syscall.Getwd()
+		if useSyscallwd(e) {
+			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 := Stat(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 := Stat("/")
+	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 := Open(parent)
+		if err != nil {
+			return "", err
+		}
+
+		for {
+			names, err := fd.Readdirnames(100)
+			if err != nil {
+				fd.Close()
+				return "", err
+			}
+			for _, name := range names {
+				d, _ := Lstat(parent + "/" + name)
+				if SameFile(d, dot) {
+					dir = "/" + name + dir
+					goto Found
+				}
+			}
+		}
+
+	Found:
+		pd, err := fd.Stat()
+		if err != nil {
+			return "", err
+		}
+		fd.Close()
+		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
+}
diff --git a/src/os/getwd_darwin.go b/src/os/getwd_darwin.go
new file mode 100644
index 000000000..e51ffcd5e
--- /dev/null
+++ b/src/os/getwd_darwin.go
@@ -0,0 +1,15 @@
+// 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 "syscall"
+
+func init() {
+	useSyscallwd = useSyscallwdDarwin
+}
+
+func useSyscallwdDarwin(err error) bool {
+	return err != syscall.ENOTSUP
+}
diff --git a/src/os/os_test.go b/src/os/os_test.go
new file mode 100644
index 000000000..0224c9b01
--- /dev/null
+++ b/src/os/os_test.go
@@ -0,0 +1,1405 @@
+// 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_test
+
+import (
+	"bytes"
+	"errors"
+	"flag"
+	"fmt"
+	"io"
+	"io/ioutil"
+	. "os"
+	osexec "os/exec"
+	"path/filepath"
+	"reflect"
+	"runtime"
+	"sort"
+	"strings"
+	"syscall"
+	"testing"
+	"text/template"
+	"time"
+)
+
+var supportsSymlinks = true
+
+var dot = []string{
+	"dir_unix.go",
+	"env.go",
+	"error.go",
+	"file.go",
+	"os_test.go",
+	"types.go",
+	"stat_darwin.go",
+	"stat_linux.go",
+}
+
+type sysDir struct {
+	name  string
+	files []string
+}
+
+var sysdir = func() (sd *sysDir) {
+	switch runtime.GOOS {
+	case "android":
+		sd = &sysDir{
+			"/system/etc",
+			[]string{
+				"audio_policy.conf",
+				"system_fonts.xml",
+			},
+		}
+	case "windows":
+		sd = &sysDir{
+			Getenv("SystemRoot") + "\\system32\\drivers\\etc",
+			[]string{
+				"networks",
+				"protocol",
+				"services",
+			},
+		}
+	case "plan9":
+		sd = &sysDir{
+			"/lib/ndb",
+			[]string{
+				"common",
+				"local",
+			},
+		}
+	default:
+		sd = &sysDir{
+			"/etc",
+			[]string{
+				"group",
+				"hosts",
+				"passwd",
+			},
+		}
+	}
+	return
+}()
+
+func size(name string, t *testing.T) int64 {
+	file, err := Open(name)
+	if err != nil {
+		t.Fatal("open failed:", err)
+	}
+	defer file.Close()
+	var buf [100]byte
+	len := 0
+	for {
+		n, e := file.Read(buf[0:])
+		len += n
+		if e == io.EOF {
+			break
+		}
+		if e != nil {
+			t.Fatal("read failed:", err)
+		}
+	}
+	return int64(len)
+}
+
+func equal(name1, name2 string) (r bool) {
+	switch runtime.GOOS {
+	case "windows":
+		r = strings.ToLower(name1) == strings.ToLower(name2)
+	default:
+		r = name1 == name2
+	}
+	return
+}
+
+func newFile(testName string, t *testing.T) (f *File) {
+	// Use a local file system, not NFS.
+	// On Unix, override $TMPDIR in case the user
+	// has it set to an NFS-mounted directory.
+	dir := ""
+	if runtime.GOOS != "android" && runtime.GOOS != "windows" {
+		dir = "/tmp"
+	}
+	f, err := ioutil.TempFile(dir, "_Go_"+testName)
+	if err != nil {
+		t.Fatalf("open %s: %s", testName, err)
+	}
+	return
+}
+
+var sfdir = sysdir.name
+var sfname = sysdir.files[0]
+
+func TestStat(t *testing.T) {
+	path := sfdir + "/" + sfname
+	dir, err := Stat(path)
+	if err != nil {
+		t.Fatal("stat failed:", err)
+	}
+	if !equal(sfname, dir.Name()) {
+		t.Error("name should be ", sfname, "; is", dir.Name())
+	}
+	filesize := size(path, t)
+	if dir.Size() != filesize {
+		t.Error("size should be", filesize, "; is", dir.Size())
+	}
+}
+
+func TestFstat(t *testing.T) {
+	path := sfdir + "/" + sfname
+	file, err1 := Open(path)
+	if err1 != nil {
+		t.Fatal("open failed:", err1)
+	}
+	defer file.Close()
+	dir, err2 := file.Stat()
+	if err2 != nil {
+		t.Fatal("fstat failed:", err2)
+	}
+	if !equal(sfname, dir.Name()) {
+		t.Error("name should be ", sfname, "; is", dir.Name())
+	}
+	filesize := size(path, t)
+	if dir.Size() != filesize {
+		t.Error("size should be", filesize, "; is", dir.Size())
+	}
+}
+
+func TestLstat(t *testing.T) {
+	path := sfdir + "/" + sfname
+	dir, err := Lstat(path)
+	if err != nil {
+		t.Fatal("lstat failed:", err)
+	}
+	if !equal(sfname, dir.Name()) {
+		t.Error("name should be ", sfname, "; is", dir.Name())
+	}
+	filesize := size(path, t)
+	if dir.Size() != filesize {
+		t.Error("size should be", filesize, "; is", dir.Size())
+	}
+}
+
+// Read with length 0 should not return EOF.
+func TestRead0(t *testing.T) {
+	path := sfdir + "/" + sfname
+	f, err := Open(path)
+	if err != nil {
+		t.Fatal("open failed:", err)
+	}
+	defer f.Close()
+
+	b := make([]byte, 0)
+	n, err := f.Read(b)
+	if n != 0 || err != nil {
+		t.Errorf("Read(0) = %d, %v, want 0, nil", n, err)
+	}
+	b = make([]byte, 100)
+	n, err = f.Read(b)
+	if n <= 0 || err != nil {
+		t.Errorf("Read(100) = %d, %v, want >0, nil", n, err)
+	}
+}
+
+func testReaddirnames(dir string, contents []string, t *testing.T) {
+	file, err := Open(dir)
+	if err != nil {
+		t.Fatalf("open %q failed: %v", dir, err)
+	}
+	defer file.Close()
+	s, err2 := file.Readdirnames(-1)
+	if err2 != nil {
+		t.Fatalf("readdirnames %q failed: %v", dir, err2)
+	}
+	for _, m := range contents {
+		found := false
+		for _, n := range s {
+			if n == "." || n == ".." {
+				t.Errorf("got %s in directory", n)
+			}
+			if equal(m, n) {
+				if found {
+					t.Error("present twice:", m)
+				}
+				found = true
+			}
+		}
+		if !found {
+			t.Error("could not find", m)
+		}
+	}
+}
+
+func testReaddir(dir string, contents []string, t *testing.T) {
+	file, err := Open(dir)
+	if err != nil {
+		t.Fatalf("open %q failed: %v", dir, err)
+	}
+	defer file.Close()
+	s, err2 := file.Readdir(-1)
+	if err2 != nil {
+		t.Fatalf("readdir %q failed: %v", dir, err2)
+	}
+	for _, m := range contents {
+		found := false
+		for _, n := range s {
+			if equal(m, n.Name()) {
+				if found {
+					t.Error("present twice:", m)
+				}
+				found = true
+			}
+		}
+		if !found {
+			t.Error("could not find", m)
+		}
+	}
+}
+
+func TestReaddirnames(t *testing.T) {
+	testReaddirnames(".", dot, t)
+	testReaddirnames(sysdir.name, sysdir.files, t)
+}
+
+func TestReaddir(t *testing.T) {
+	testReaddir(".", dot, t)
+	testReaddir(sysdir.name, sysdir.files, t)
+}
+
+// Read the directory one entry at a time.
+func smallReaddirnames(file *File, length int, t *testing.T) []string {
+	names := make([]string, length)
+	count := 0
+	for {
+		d, err := file.Readdirnames(1)
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			t.Fatalf("readdirnames %q failed: %v", file.Name(), err)
+		}
+		if len(d) == 0 {
+			t.Fatalf("readdirnames %q returned empty slice and no error", file.Name())
+		}
+		names[count] = d[0]
+		count++
+	}
+	return names[0:count]
+}
+
+// Check that reading a directory one entry at a time gives the same result
+// as reading it all at once.
+func TestReaddirnamesOneAtATime(t *testing.T) {
+	// big directory that doesn't change often.
+	dir := "/usr/bin"
+	switch runtime.GOOS {
+	case "android":
+		dir = "/system/bin"
+	case "plan9":
+		dir = "/bin"
+	case "windows":
+		dir = Getenv("SystemRoot") + "\\system32"
+	}
+	file, err := Open(dir)
+	if err != nil {
+		t.Fatalf("open %q failed: %v", dir, err)
+	}
+	defer file.Close()
+	all, err1 := file.Readdirnames(-1)
+	if err1 != nil {
+		t.Fatalf("readdirnames %q failed: %v", dir, err1)
+	}
+	file1, err2 := Open(dir)
+	if err2 != nil {
+		t.Fatalf("open %q failed: %v", dir, err2)
+	}
+	defer file1.Close()
+	small := smallReaddirnames(file1, len(all)+100, t) // +100 in case we screw up
+	if len(small) < len(all) {
+		t.Fatalf("len(small) is %d, less than %d", len(small), len(all))
+	}
+	for i, n := range all {
+		if small[i] != n {
+			t.Errorf("small read %q mismatch: %v", small[i], n)
+		}
+	}
+}
+
+func TestReaddirNValues(t *testing.T) {
+	if testing.Short() {
+		t.Skip("test.short; skipping")
+	}
+	dir, err := ioutil.TempDir("", "")
+	if err != nil {
+		t.Fatalf("TempDir: %v", err)
+	}
+	defer RemoveAll(dir)
+	for i := 1; i <= 105; i++ {
+		f, err := Create(filepath.Join(dir, fmt.Sprintf("%d", i)))
+		if err != nil {
+			t.Fatalf("Create: %v", err)
+		}
+		f.Write([]byte(strings.Repeat("X", i)))
+		f.Close()
+	}
+
+	var d *File
+	openDir := func() {
+		var err error
+		d, err = Open(dir)
+		if err != nil {
+			t.Fatalf("Open directory: %v", err)
+		}
+	}
+
+	readDirExpect := func(n, want int, wantErr error) {
+		fi, err := d.Readdir(n)
+		if err != wantErr {
+			t.Fatalf("Readdir of %d got error %v, want %v", n, err, wantErr)
+		}
+		if g, e := len(fi), want; g != e {
+			t.Errorf("Readdir of %d got %d files, want %d", n, g, e)
+		}
+	}
+
+	readDirNamesExpect := func(n, want int, wantErr error) {
+		fi, err := d.Readdirnames(n)
+		if err != wantErr {
+			t.Fatalf("Readdirnames of %d got error %v, want %v", n, err, wantErr)
+		}
+		if g, e := len(fi), want; g != e {
+			t.Errorf("Readdirnames of %d got %d files, want %d", n, g, e)
+		}
+	}
+
+	for _, fn := range []func(int, int, error){readDirExpect, readDirNamesExpect} {
+		// Test the slurp case
+		openDir()
+		fn(0, 105, nil)
+		fn(0, 0, nil)
+		d.Close()
+
+		// Slurp with -1 instead
+		openDir()
+		fn(-1, 105, nil)
+		fn(-2, 0, nil)
+		fn(0, 0, nil)
+		d.Close()
+
+		// Test the bounded case
+		openDir()
+		fn(1, 1, nil)
+		fn(2, 2, nil)
+		fn(105, 102, nil) // and tests buffer >100 case
+		fn(3, 0, io.EOF)
+		d.Close()
+	}
+}
+
+func touch(t *testing.T, name string) {
+	f, err := Create(name)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := f.Close(); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestReaddirStatFailures(t *testing.T) {
+	switch runtime.GOOS {
+	case "windows", "plan9":
+		// Windows and Plan 9 already do this correctly,
+		// but are structured with different syscalls such
+		// that they don't use Lstat, so the hook below for
+		// testing it wouldn't work.
+		t.Skipf("skipping test on %v", runtime.GOOS)
+	}
+	dir, err := ioutil.TempDir("", "")
+	if err != nil {
+		t.Fatalf("TempDir: %v", err)
+	}
+	defer RemoveAll(dir)
+	touch(t, filepath.Join(dir, "good1"))
+	touch(t, filepath.Join(dir, "x")) // will disappear or have an error
+	touch(t, filepath.Join(dir, "good2"))
+	defer func() {
+		*LstatP = Lstat
+	}()
+	var xerr error // error to return for x
+	*LstatP = func(path string) (FileInfo, error) {
+		if xerr != nil && strings.HasSuffix(path, "x") {
+			return nil, xerr
+		}
+		return Lstat(path)
+	}
+	readDir := func() ([]FileInfo, error) {
+		d, err := Open(dir)
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer d.Close()
+		return d.Readdir(-1)
+	}
+	mustReadDir := func(testName string) []FileInfo {
+		fis, err := readDir()
+		if err != nil {
+			t.Fatalf("%s: Readdir: %v", testName, err)
+		}
+		return fis
+	}
+	names := func(fis []FileInfo) []string {
+		s := make([]string, len(fis))
+		for i, fi := range fis {
+			s[i] = fi.Name()
+		}
+		sort.Strings(s)
+		return s
+	}
+
+	if got, want := names(mustReadDir("inital readdir")),
+		[]string{"good1", "good2", "x"}; !reflect.DeepEqual(got, want) {
+		t.Errorf("initial readdir got %q; want %q", got, want)
+	}
+
+	xerr = ErrNotExist
+	if got, want := names(mustReadDir("with x disappearing")),
+		[]string{"good1", "good2"}; !reflect.DeepEqual(got, want) {
+		t.Errorf("with x disappearing, got %q; want %q", got, want)
+	}
+
+	xerr = errors.New("some real error")
+	if _, err := readDir(); err != xerr {
+		t.Errorf("with a non-ErrNotExist error, got error %v; want %v", err, xerr)
+	}
+}
+
+func TestHardLink(t *testing.T) {
+	// Hardlinks are not supported under windows or Plan 9.
+	if runtime.GOOS == "plan9" {
+		return
+	}
+	from, to := "hardlinktestfrom", "hardlinktestto"
+	Remove(from) // Just in case.
+	file, err := Create(to)
+	if err != nil {
+		t.Fatalf("open %q failed: %v", to, err)
+	}
+	defer Remove(to)
+	if err = file.Close(); err != nil {
+		t.Errorf("close %q failed: %v", to, err)
+	}
+	err = Link(to, from)
+	if err != nil {
+		t.Fatalf("link %q, %q failed: %v", to, from, err)
+	}
+	defer Remove(from)
+	tostat, err := Stat(to)
+	if err != nil {
+		t.Fatalf("stat %q failed: %v", to, err)
+	}
+	fromstat, err := Stat(from)
+	if err != nil {
+		t.Fatalf("stat %q failed: %v", from, err)
+	}
+	if !SameFile(tostat, fromstat) {
+		t.Errorf("link %q, %q did not create hard link", to, from)
+	}
+}
+
+func TestSymlink(t *testing.T) {
+	switch runtime.GOOS {
+	case "android", "nacl", "plan9":
+		t.Skipf("skipping on %s", runtime.GOOS)
+	case "windows":
+		if !supportsSymlinks {
+			t.Skipf("skipping on %s", runtime.GOOS)
+		}
+	}
+	from, to := "symlinktestfrom", "symlinktestto"
+	Remove(from) // Just in case.
+	file, err := Create(to)
+	if err != nil {
+		t.Fatalf("open %q failed: %v", to, err)
+	}
+	defer Remove(to)
+	if err = file.Close(); err != nil {
+		t.Errorf("close %q failed: %v", to, err)
+	}
+	err = Symlink(to, from)
+	if err != nil {
+		t.Fatalf("symlink %q, %q failed: %v", to, from, err)
+	}
+	defer Remove(from)
+	tostat, err := Lstat(to)
+	if err != nil {
+		t.Fatalf("stat %q failed: %v", to, err)
+	}
+	if tostat.Mode()&ModeSymlink != 0 {
+		t.Fatalf("stat %q claims to have found a symlink", to)
+	}
+	fromstat, err := Stat(from)
+	if err != nil {
+		t.Fatalf("stat %q failed: %v", from, err)
+	}
+	if !SameFile(tostat, fromstat) {
+		t.Errorf("symlink %q, %q did not create symlink", to, from)
+	}
+	fromstat, err = Lstat(from)
+	if err != nil {
+		t.Fatalf("lstat %q failed: %v", from, err)
+	}
+	if fromstat.Mode()&ModeSymlink == 0 {
+		t.Fatalf("symlink %q, %q did not create symlink", to, from)
+	}
+	fromstat, err = Stat(from)
+	if err != nil {
+		t.Fatalf("stat %q failed: %v", from, err)
+	}
+	if fromstat.Mode()&ModeSymlink != 0 {
+		t.Fatalf("stat %q did not follow symlink", from)
+	}
+	s, err := Readlink(from)
+	if err != nil {
+		t.Fatalf("readlink %q failed: %v", from, err)
+	}
+	if s != to {
+		t.Fatalf("after symlink %q != %q", s, to)
+	}
+	file, err = Open(from)
+	if err != nil {
+		t.Fatalf("open %q failed: %v", from, err)
+	}
+	file.Close()
+}
+
+func TestLongSymlink(t *testing.T) {
+	switch runtime.GOOS {
+	case "plan9", "nacl":
+		t.Skipf("skipping on %s", runtime.GOOS)
+	case "windows":
+		if !supportsSymlinks {
+			t.Skipf("skipping on %s", runtime.GOOS)
+		}
+	}
+	s := "0123456789abcdef"
+	// Long, but not too long: a common limit is 255.
+	s = s + s + s + s + s + s + s + s + s + s + s + s + s + s + s
+	from := "longsymlinktestfrom"
+	Remove(from) // Just in case.
+	err := Symlink(s, from)
+	if err != nil {
+		t.Fatalf("symlink %q, %q failed: %v", s, from, err)
+	}
+	defer Remove(from)
+	r, err := Readlink(from)
+	if err != nil {
+		t.Fatalf("readlink %q failed: %v", from, err)
+	}
+	if r != s {
+		t.Fatalf("after symlink %q != %q", r, s)
+	}
+}
+
+func TestRename(t *testing.T) {
+	from, to := "renamefrom", "renameto"
+	Remove(to) // Just in case.
+	file, err := Create(from)
+	if err != nil {
+		t.Fatalf("open %q failed: %v", to, err)
+	}
+	if err = file.Close(); err != nil {
+		t.Errorf("close %q failed: %v", to, err)
+	}
+	err = Rename(from, to)
+	if err != nil {
+		t.Fatalf("rename %q, %q failed: %v", to, from, err)
+	}
+	defer Remove(to)
+	_, err = Stat(to)
+	if err != nil {
+		t.Errorf("stat %q failed: %v", to, err)
+	}
+}
+
+func exec(t *testing.T, dir, cmd string, args []string, expect string) {
+	r, w, err := Pipe()
+	if err != nil {
+		t.Fatalf("Pipe: %v", err)
+	}
+	defer r.Close()
+	attr := &ProcAttr{Dir: dir, Files: []*File{nil, w, Stderr}}
+	p, err := StartProcess(cmd, args, attr)
+	if err != nil {
+		t.Fatalf("StartProcess: %v", err)
+	}
+	w.Close()
+
+	var b bytes.Buffer
+	io.Copy(&b, r)
+	output := b.String()
+
+	fi1, _ := Stat(strings.TrimSpace(output))
+	fi2, _ := Stat(expect)
+	if !SameFile(fi1, fi2) {
+		t.Errorf("exec %q returned %q wanted %q",
+			strings.Join(append([]string{cmd}, args...), " "), output, expect)
+	}
+	p.Wait()
+}
+
+func TestStartProcess(t *testing.T) {
+	switch runtime.GOOS {
+	case "android", "nacl":
+		t.Skipf("skipping on %s", runtime.GOOS)
+	}
+
+	var dir, cmd string
+	var args []string
+	if runtime.GOOS == "windows" {
+		cmd = Getenv("COMSPEC")
+		dir = Getenv("SystemRoot")
+		args = []string{"/c", "cd"}
+	} else {
+		cmd = "/bin/pwd"
+		dir = "/"
+		args = []string{}
+	}
+	cmddir, cmdbase := filepath.Split(cmd)
+	args = append([]string{cmdbase}, args...)
+	// Test absolute executable path.
+	exec(t, dir, cmd, args, dir)
+	// Test relative executable path.
+	exec(t, cmddir, cmdbase, args, cmddir)
+}
+
+func checkMode(t *testing.T, path string, mode FileMode) {
+	dir, err := Stat(path)
+	if err != nil {
+		t.Fatalf("Stat %q (looking for mode %#o): %s", path, mode, err)
+	}
+	if dir.Mode()&0777 != mode {
+		t.Errorf("Stat %q: mode %#o want %#o", path, dir.Mode(), mode)
+	}
+}
+
+func TestChmod(t *testing.T) {
+	// Chmod is not supported under windows.
+	if runtime.GOOS == "windows" {
+		return
+	}
+	f := newFile("TestChmod", t)
+	defer Remove(f.Name())
+	defer f.Close()
+
+	if err := Chmod(f.Name(), 0456); err != nil {
+		t.Fatalf("chmod %s 0456: %s", f.Name(), err)
+	}
+	checkMode(t, f.Name(), 0456)
+
+	if err := f.Chmod(0123); err != nil {
+		t.Fatalf("chmod %s 0123: %s", f.Name(), err)
+	}
+	checkMode(t, f.Name(), 0123)
+}
+
+func checkSize(t *testing.T, f *File, size int64) {
+	dir, err := f.Stat()
+	if err != nil {
+		t.Fatalf("Stat %q (looking for size %d): %s", f.Name(), size, err)
+	}
+	if dir.Size() != size {
+		t.Errorf("Stat %q: size %d want %d", f.Name(), dir.Size(), size)
+	}
+}
+
+func TestFTruncate(t *testing.T) {
+	f := newFile("TestFTruncate", t)
+	defer Remove(f.Name())
+	defer f.Close()
+
+	checkSize(t, f, 0)
+	f.Write([]byte("hello, world\n"))
+	checkSize(t, f, 13)
+	f.Truncate(10)
+	checkSize(t, f, 10)
+	f.Truncate(1024)
+	checkSize(t, f, 1024)
+	f.Truncate(0)
+	checkSize(t, f, 0)
+	_, err := f.Write([]byte("surprise!"))
+	if err == nil {
+		checkSize(t, f, 13+9) // wrote at offset past where hello, world was.
+	}
+}
+
+func TestTruncate(t *testing.T) {
+	f := newFile("TestTruncate", t)
+	defer Remove(f.Name())
+	defer f.Close()
+
+	checkSize(t, f, 0)
+	f.Write([]byte("hello, world\n"))
+	checkSize(t, f, 13)
+	Truncate(f.Name(), 10)
+	checkSize(t, f, 10)
+	Truncate(f.Name(), 1024)
+	checkSize(t, f, 1024)
+	Truncate(f.Name(), 0)
+	checkSize(t, f, 0)
+	_, err := f.Write([]byte("surprise!"))
+	if err == nil {
+		checkSize(t, f, 13+9) // wrote at offset past where hello, world was.
+	}
+}
+
+// Use TempDir() to make sure we're on a local file system,
+// so that timings are not distorted by latency and caching.
+// On NFS, timings can be off due to caching of meta-data on
+// NFS servers (Issue 848).
+func TestChtimes(t *testing.T) {
+	f := newFile("TestChtimes", t)
+	defer Remove(f.Name())
+	defer f.Close()
+
+	f.Write([]byte("hello, world\n"))
+	f.Close()
+
+	st, err := Stat(f.Name())
+	if err != nil {
+		t.Fatalf("Stat %s: %s", f.Name(), err)
+	}
+	preStat := st
+
+	// Move access and modification time back a second
+	at := Atime(preStat)
+	mt := preStat.ModTime()
+	err = Chtimes(f.Name(), at.Add(-time.Second), mt.Add(-time.Second))
+	if err != nil {
+		t.Fatalf("Chtimes %s: %s", f.Name(), err)
+	}
+
+	st, err = Stat(f.Name())
+	if err != nil {
+		t.Fatalf("second Stat %s: %s", f.Name(), err)
+	}
+	postStat := st
+
+	/* Plan 9, NaCl:
+		Mtime is the time of the last change of content.  Similarly, atime is set whenever the
+	    contents are accessed; also, it is set whenever mtime is set.
+	*/
+	pat := Atime(postStat)
+	pmt := postStat.ModTime()
+	if !pat.Before(at) && runtime.GOOS != "plan9" && runtime.GOOS != "nacl" {
+		t.Errorf("AccessTime didn't go backwards; was=%d, after=%d", at, pat)
+	}
+
+	if !pmt.Before(mt) {
+		t.Errorf("ModTime didn't go backwards; was=%d, after=%d", mt, pmt)
+	}
+}
+
+func TestChdirAndGetwd(t *testing.T) {
+	// TODO(brainman): file.Chdir() is not implemented on windows.
+	if runtime.GOOS == "windows" {
+		return
+	}
+	fd, err := Open(".")
+	if err != nil {
+		t.Fatalf("Open .: %s", err)
+	}
+	// These are chosen carefully not to be symlinks on a Mac
+	// (unlike, say, /var, /etc), except /tmp, which we handle below.
+	dirs := []string{"/", "/usr/bin", "/tmp"}
+	// /usr/bin does not usually exist on Plan 9 or Android.
+	switch runtime.GOOS {
+	case "android":
+		dirs = []string{"/", "/system/bin"}
+	case "plan9":
+		dirs = []string{"/", "/usr"}
+	}
+	oldwd := Getenv("PWD")
+	for mode := 0; mode < 2; mode++ {
+		for _, d := range dirs {
+			if mode == 0 {
+				err = Chdir(d)
+			} else {
+				fd1, err := Open(d)
+				if err != nil {
+					t.Errorf("Open %s: %s", d, err)
+					continue
+				}
+				err = fd1.Chdir()
+				fd1.Close()
+			}
+			if d == "/tmp" {
+				Setenv("PWD", "/tmp")
+			}
+			pwd, err1 := Getwd()
+			Setenv("PWD", oldwd)
+			err2 := fd.Chdir()
+			if err2 != nil {
+				// We changed the current directory and cannot go back.
+				// Don't let the tests continue; they'll scribble
+				// all over some other directory.
+				fmt.Fprintf(Stderr, "fchdir back to dot failed: %s\n", err2)
+				Exit(1)
+			}
+			if err != nil {
+				fd.Close()
+				t.Fatalf("Chdir %s: %s", d, err)
+			}
+			if err1 != nil {
+				fd.Close()
+				t.Fatalf("Getwd in %s: %s", d, err1)
+			}
+			if pwd != d {
+				fd.Close()
+				t.Fatalf("Getwd returned %q want %q", pwd, d)
+			}
+		}
+	}
+	fd.Close()
+}
+
+func TestSeek(t *testing.T) {
+	f := newFile("TestSeek", t)
+	defer Remove(f.Name())
+	defer f.Close()
+
+	const data = "hello, world\n"
+	io.WriteString(f, data)
+
+	type test struct {
+		in     int64
+		whence int
+		out    int64
+	}
+	var tests = []test{
+		{0, 1, int64(len(data))},
+		{0, 0, 0},
+		{5, 0, 5},
+		{0, 2, int64(len(data))},
+		{0, 0, 0},
+		{-1, 2, int64(len(data)) - 1},
+		{1 << 33, 0, 1 << 33},
+		{1 << 33, 2, 1<<33 + int64(len(data))},
+	}
+	for i, tt := range tests {
+		off, err := f.Seek(tt.in, tt.whence)
+		if off != tt.out || err != nil {
+			if e, ok := err.(*PathError); ok && e.Err == syscall.EINVAL && tt.out > 1<<32 {
+				// Reiserfs rejects the big seeks.
+				// http://code.google.com/p/go/issues/detail?id=91
+				break
+			}
+			t.Errorf("#%d: Seek(%v, %v) = %v, %v want %v, nil", i, tt.in, tt.whence, off, err, tt.out)
+		}
+	}
+}
+
+type openErrorTest struct {
+	path  string
+	mode  int
+	error error
+}
+
+var openErrorTests = []openErrorTest{
+	{
+		sfdir + "/no-such-file",
+		O_RDONLY,
+		syscall.ENOENT,
+	},
+	{
+		sfdir,
+		O_WRONLY,
+		syscall.EISDIR,
+	},
+	{
+		sfdir + "/" + sfname + "/no-such-file",
+		O_WRONLY,
+		syscall.ENOTDIR,
+	},
+}
+
+func TestOpenError(t *testing.T) {
+	for _, tt := range openErrorTests {
+		f, err := OpenFile(tt.path, tt.mode, 0)
+		if err == nil {
+			t.Errorf("Open(%q, %d) succeeded", tt.path, tt.mode)
+			f.Close()
+			continue
+		}
+		perr, ok := err.(*PathError)
+		if !ok {
+			t.Errorf("Open(%q, %d) returns error of %T type; want *PathError", tt.path, tt.mode, err)
+		}
+		if perr.Err != tt.error {
+			if runtime.GOOS == "plan9" {
+				syscallErrStr := perr.Err.Error()
+				expectedErrStr := strings.Replace(tt.error.Error(), "file ", "", 1)
+				if !strings.HasSuffix(syscallErrStr, expectedErrStr) {
+					// Some Plan 9 file servers incorrectly return
+					// EACCES rather than EISDIR when a directory is
+					// opened for write.
+					if tt.error == syscall.EISDIR && strings.HasSuffix(syscallErrStr, syscall.EACCES.Error()) {
+						continue
+					}
+					t.Errorf("Open(%q, %d) = _, %q; want suffix %q", tt.path, tt.mode, syscallErrStr, expectedErrStr)
+				}
+				continue
+			}
+			if runtime.GOOS == "dragonfly" {
+				// DragonFly incorrectly returns EACCES rather
+				// EISDIR when a directory is opened for write.
+				if tt.error == syscall.EISDIR && perr.Err == syscall.EACCES {
+					continue
+				}
+			}
+			t.Errorf("Open(%q, %d) = _, %q; want %q", tt.path, tt.mode, perr.Err.Error(), tt.error.Error())
+		}
+	}
+}
+
+func TestOpenNoName(t *testing.T) {
+	f, err := Open("")
+	if err == nil {
+		t.Fatal(`Open("") succeeded`)
+		f.Close()
+	}
+}
+
+func run(t *testing.T, cmd []string) string {
+	// Run /bin/hostname and collect output.
+	r, w, err := Pipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer r.Close()
+	p, err := StartProcess("/bin/hostname", []string{"hostname"}, &ProcAttr{Files: []*File{nil, w, Stderr}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	w.Close()
+
+	var b bytes.Buffer
+	io.Copy(&b, r)
+	_, err = p.Wait()
+	if err != nil {
+		t.Fatalf("run hostname Wait: %v", err)
+	}
+	err = p.Kill()
+	if err == nil {
+		t.Errorf("expected an error from Kill running 'hostname'")
+	}
+	output := b.String()
+	if n := len(output); n > 0 && output[n-1] == '\n' {
+		output = output[0 : n-1]
+	}
+	if output == "" {
+		t.Fatalf("%v produced no output", cmd)
+	}
+
+	return output
+}
+
+func TestHostname(t *testing.T) {
+	// There is no other way to fetch hostname on windows, but via winapi.
+	// On Plan 9 it can be taken from #c/sysname as Hostname() does.
+	switch runtime.GOOS {
+	case "android", "nacl", "plan9", "windows":
+		t.Skipf("skipping on %s", runtime.GOOS)
+	}
+
+	// Check internal Hostname() against the output of /bin/hostname.
+	// Allow that the internal Hostname returns a Fully Qualified Domain Name
+	// and the /bin/hostname only returns the first component
+	hostname, err := Hostname()
+	if err != nil {
+		t.Fatalf("%v", err)
+	}
+	want := run(t, []string{"/bin/hostname"})
+	if hostname != want {
+		i := strings.Index(hostname, ".")
+		if i < 0 || hostname[0:i] != want {
+			t.Errorf("Hostname() = %q, want %q", hostname, want)
+		}
+	}
+}
+
+func TestReadAt(t *testing.T) {
+	f := newFile("TestReadAt", t)
+	defer Remove(f.Name())
+	defer f.Close()
+
+	const data = "hello, world\n"
+	io.WriteString(f, data)
+
+	b := make([]byte, 5)
+	n, err := f.ReadAt(b, 7)
+	if err != nil || n != len(b) {
+		t.Fatalf("ReadAt 7: %d, %v", n, err)
+	}
+	if string(b) != "world" {
+		t.Fatalf("ReadAt 7: have %q want %q", string(b), "world")
+	}
+}
+
+func TestWriteAt(t *testing.T) {
+	f := newFile("TestWriteAt", t)
+	defer Remove(f.Name())
+	defer f.Close()
+
+	const data = "hello, world\n"
+	io.WriteString(f, data)
+
+	n, err := f.WriteAt([]byte("WORLD"), 7)
+	if err != nil || n != 5 {
+		t.Fatalf("WriteAt 7: %d, %v", n, err)
+	}
+
+	b, err := ioutil.ReadFile(f.Name())
+	if err != nil {
+		t.Fatalf("ReadFile %s: %v", f.Name(), err)
+	}
+	if string(b) != "hello, WORLD\n" {
+		t.Fatalf("after write: have %q want %q", string(b), "hello, WORLD\n")
+	}
+}
+
+func writeFile(t *testing.T, fname string, flag int, text string) string {
+	f, err := OpenFile(fname, flag, 0666)
+	if err != nil {
+		t.Fatalf("Open: %v", err)
+	}
+	n, err := io.WriteString(f, text)
+	if err != nil {
+		t.Fatalf("WriteString: %d, %v", n, err)
+	}
+	f.Close()
+	data, err := ioutil.ReadFile(fname)
+	if err != nil {
+		t.Fatalf("ReadFile: %v", err)
+	}
+	return string(data)
+}
+
+func TestAppend(t *testing.T) {
+	const f = "append.txt"
+	defer Remove(f)
+	s := writeFile(t, f, O_CREATE|O_TRUNC|O_RDWR, "new")
+	if s != "new" {
+		t.Fatalf("writeFile: have %q want %q", s, "new")
+	}
+	s = writeFile(t, f, O_APPEND|O_RDWR, "|append")
+	if s != "new|append" {
+		t.Fatalf("writeFile: have %q want %q", s, "new|append")
+	}
+	s = writeFile(t, f, O_CREATE|O_APPEND|O_RDWR, "|append")
+	if s != "new|append|append" {
+		t.Fatalf("writeFile: have %q want %q", s, "new|append|append")
+	}
+	err := Remove(f)
+	if err != nil {
+		t.Fatalf("Remove: %v", err)
+	}
+	s = writeFile(t, f, O_CREATE|O_APPEND|O_RDWR, "new&append")
+	if s != "new&append" {
+		t.Fatalf("writeFile: after append have %q want %q", s, "new&append")
+	}
+	s = writeFile(t, f, O_CREATE|O_RDWR, "old")
+	if s != "old&append" {
+		t.Fatalf("writeFile: after create have %q want %q", s, "old&append")
+	}
+	s = writeFile(t, f, O_CREATE|O_TRUNC|O_RDWR, "new")
+	if s != "new" {
+		t.Fatalf("writeFile: after truncate have %q want %q", s, "new")
+	}
+}
+
+func TestStatDirWithTrailingSlash(t *testing.T) {
+	// Create new temporary directory and arrange to clean it up.
+	path, err := ioutil.TempDir("", "/_TestStatDirWithSlash_")
+	if err != nil {
+		t.Fatalf("TempDir: %s", err)
+	}
+	defer RemoveAll(path)
+
+	// Stat of path should succeed.
+	_, err = Stat(path)
+	if err != nil {
+		t.Fatalf("stat %s failed: %s", path, err)
+	}
+
+	// Stat of path+"/" should succeed too.
+	path += "/"
+	_, err = Stat(path)
+	if err != nil {
+		t.Fatalf("stat %s failed: %s", path, err)
+	}
+}
+
+func TestNilProcessStateString(t *testing.T) {
+	var ps *ProcessState
+	s := ps.String()
+	if s != "<nil>" {
+		t.Errorf("(*ProcessState)(nil).String() = %q, want %q", s, "<nil>")
+	}
+}
+
+func TestSameFile(t *testing.T) {
+	fa, err := Create("a")
+	if err != nil {
+		t.Fatalf("Create(a): %v", err)
+	}
+	defer Remove(fa.Name())
+	fa.Close()
+	fb, err := Create("b")
+	if err != nil {
+		t.Fatalf("Create(b): %v", err)
+	}
+	defer Remove(fb.Name())
+	fb.Close()
+
+	ia1, err := Stat("a")
+	if err != nil {
+		t.Fatalf("Stat(a): %v", err)
+	}
+	ia2, err := Stat("a")
+	if err != nil {
+		t.Fatalf("Stat(a): %v", err)
+	}
+	if !SameFile(ia1, ia2) {
+		t.Errorf("files should be same")
+	}
+
+	ib, err := Stat("b")
+	if err != nil {
+		t.Fatalf("Stat(b): %v", err)
+	}
+	if SameFile(ia1, ib) {
+		t.Errorf("files should be different")
+	}
+}
+
+func TestDevNullFile(t *testing.T) {
+	f, err := Open(DevNull)
+	if err != nil {
+		t.Fatalf("Open(%s): %v", DevNull, err)
+	}
+	defer f.Close()
+	fi, err := f.Stat()
+	if err != nil {
+		t.Fatalf("Stat(%s): %v", DevNull, err)
+	}
+	name := filepath.Base(DevNull)
+	if fi.Name() != name {
+		t.Fatalf("wrong file name have %v want %v", fi.Name(), name)
+	}
+	if fi.Size() != 0 {
+		t.Fatalf("wrong file size have %d want 0", fi.Size())
+	}
+}
+
+var testLargeWrite = flag.Bool("large_write", false, "run TestLargeWriteToConsole test that floods console with output")
+
+func TestLargeWriteToConsole(t *testing.T) {
+	if !*testLargeWrite {
+		t.Skip("skipping console-flooding test; enable with -large_write")
+	}
+	b := make([]byte, 32000)
+	for i := range b {
+		b[i] = '.'
+	}
+	b[len(b)-1] = '\n'
+	n, err := Stdout.Write(b)
+	if err != nil {
+		t.Fatalf("Write to os.Stdout failed: %v", err)
+	}
+	if n != len(b) {
+		t.Errorf("Write to os.Stdout should return %d; got %d", len(b), n)
+	}
+	n, err = Stderr.Write(b)
+	if err != nil {
+		t.Fatalf("Write to os.Stderr failed: %v", err)
+	}
+	if n != len(b) {
+		t.Errorf("Write to os.Stderr should return %d; got %d", len(b), n)
+	}
+}
+
+func TestStatDirModeExec(t *testing.T) {
+	const mode = 0111
+
+	path, err := ioutil.TempDir("", "go-build")
+	if err != nil {
+		t.Fatalf("Failed to create temp directory: %v", err)
+	}
+	defer RemoveAll(path)
+
+	if err := Chmod(path, 0777); err != nil {
+		t.Fatalf("Chmod %q 0777: %v", path, err)
+	}
+
+	dir, err := Stat(path)
+	if err != nil {
+		t.Fatalf("Stat %q (looking for mode %#o): %s", path, mode, err)
+	}
+	if dir.Mode()&mode != mode {
+		t.Errorf("Stat %q: mode %#o want %#o", path, dir.Mode()&mode, mode)
+	}
+}
+
+func TestReadAtEOF(t *testing.T) {
+	f := newFile("TestReadAtEOF", t)
+	defer Remove(f.Name())
+	defer f.Close()
+
+	_, err := f.ReadAt(make([]byte, 10), 0)
+	switch err {
+	case io.EOF:
+		// all good
+	case nil:
+		t.Fatalf("ReadAt succeeded")
+	default:
+		t.Fatalf("ReadAt failed: %s", err)
+	}
+}
+
+func testKillProcess(t *testing.T, processKiller func(p *Process)) {
+	switch runtime.GOOS {
+	case "android", "nacl":
+		t.Skipf("skipping on %s", runtime.GOOS)
+	}
+
+	dir, err := ioutil.TempDir("", "go-build")
+	if err != nil {
+		t.Fatalf("Failed to create temp directory: %v", err)
+	}
+	defer RemoveAll(dir)
+
+	src := filepath.Join(dir, "main.go")
+	f, err := Create(src)
+	if err != nil {
+		t.Fatalf("Failed to create %v: %v", src, err)
+	}
+	st := template.Must(template.New("source").Parse(`
+package main
+import "time"
+func main() {
+	time.Sleep(time.Second)
+}
+`))
+	err = st.Execute(f, nil)
+	if err != nil {
+		f.Close()
+		t.Fatalf("Failed to execute template: %v", err)
+	}
+	f.Close()
+
+	exe := filepath.Join(dir, "main.exe")
+	output, err := osexec.Command("go", "build", "-o", exe, src).CombinedOutput()
+	if err != nil {
+		t.Fatalf("Failed to build exe %v: %v %v", exe, err, string(output))
+	}
+
+	cmd := osexec.Command(exe)
+	err = cmd.Start()
+	if err != nil {
+		t.Fatalf("Failed to start test process: %v", err)
+	}
+	go func() {
+		time.Sleep(100 * time.Millisecond)
+		processKiller(cmd.Process)
+	}()
+	err = cmd.Wait()
+	if err == nil {
+		t.Errorf("Test process succeeded, but expected to fail")
+	}
+}
+
+func TestKillStartProcess(t *testing.T) {
+	testKillProcess(t, func(p *Process) {
+		err := p.Kill()
+		if err != nil {
+			t.Fatalf("Failed to kill test process: %v", err)
+		}
+	})
+}
+
+func TestGetppid(t *testing.T) {
+	switch runtime.GOOS {
+	case "nacl":
+		t.Skip("skipping on nacl")
+	case "plan9":
+		// TODO: golang.org/issue/8206
+		t.Skipf("skipping test on plan9; see issue 8206")
+	}
+
+	if Getenv("GO_WANT_HELPER_PROCESS") == "1" {
+		fmt.Print(Getppid())
+		Exit(0)
+	}
+
+	cmd := osexec.Command(Args[0], "-test.run=TestGetppid")
+	cmd.Env = append(Environ(), "GO_WANT_HELPER_PROCESS=1")
+
+	// verify that Getppid() from the forked process reports our process id
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("Failed to spawn child process: %v %q", err, string(output))
+	}
+
+	childPpid := string(output)
+	ourPid := fmt.Sprintf("%d", Getpid())
+	if childPpid != ourPid {
+		t.Fatalf("Child process reports parent process id '%v', expected '%v'", childPpid, ourPid)
+	}
+}
+
+func TestKillFindProcess(t *testing.T) {
+	testKillProcess(t, func(p *Process) {
+		p2, err := FindProcess(p.Pid)
+		if err != nil {
+			t.Fatalf("Failed to find test process: %v", err)
+		}
+		err = p2.Kill()
+		if err != nil {
+			t.Fatalf("Failed to kill test process: %v", err)
+		}
+	})
+}
+
+var nilFileMethodTests = []struct {
+	name string
+	f    func(*File) error
+}{
+	{"Chdir", func(f *File) error { return f.Chdir() }},
+	{"Close", func(f *File) error { return f.Close() }},
+	{"Chmod", func(f *File) error { return f.Chmod(0) }},
+	{"Chown", func(f *File) error { return f.Chown(0, 0) }},
+	{"Read", func(f *File) error { _, err := f.Read(make([]byte, 0)); return err }},
+	{"ReadAt", func(f *File) error { _, err := f.ReadAt(make([]byte, 0), 0); return err }},
+	{"Readdir", func(f *File) error { _, err := f.Readdir(1); return err }},
+	{"Readdirnames", func(f *File) error { _, err := f.Readdirnames(1); return err }},
+	{"Seek", func(f *File) error { _, err := f.Seek(0, 0); return err }},
+	{"Stat", func(f *File) error { _, err := f.Stat(); return err }},
+	{"Sync", func(f *File) error { return f.Sync() }},
+	{"Truncate", func(f *File) error { return f.Truncate(0) }},
+	{"Write", func(f *File) error { _, err := f.Write(make([]byte, 0)); return err }},
+	{"WriteAt", func(f *File) error { _, err := f.WriteAt(make([]byte, 0), 0); return err }},
+	{"WriteString", func(f *File) error { _, err := f.WriteString(""); return err }},
+}
+
+// Test that all File methods give ErrInvalid if the receiver is nil.
+func TestNilFileMethods(t *testing.T) {
+	for _, tt := range nilFileMethodTests {
+		var file *File
+		got := tt.f(file)
+		if got != ErrInvalid {
+			t.Errorf("%v should fail when f is nil; got %v", tt.name, got)
+		}
+	}
+}
diff --git a/src/os/os_unix_test.go b/src/os/os_unix_test.go
new file mode 100644
index 000000000..21d40ccaf
--- /dev/null
+++ b/src/os/os_unix_test.go
@@ -0,0 +1,76 @@
+// 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.
+
+// +build darwin dragonfly freebsd linux netbsd openbsd solaris
+
+package os_test
+
+import (
+	. "os"
+	"runtime"
+	"syscall"
+	"testing"
+)
+
+func checkUidGid(t *testing.T, path string, uid, gid int) {
+	dir, err := Stat(path)
+	if err != nil {
+		t.Fatalf("Stat %q (looking for uid/gid %d/%d): %s", path, uid, gid, err)
+	}
+	sys := dir.Sys().(*syscall.Stat_t)
+	if int(sys.Uid) != uid {
+		t.Errorf("Stat %q: uid %d want %d", path, sys.Uid, uid)
+	}
+	if int(sys.Gid) != gid {
+		t.Errorf("Stat %q: gid %d want %d", path, sys.Gid, gid)
+	}
+}
+
+func TestChown(t *testing.T) {
+	// Chown is not supported under windows os Plan 9.
+	// Plan9 provides a native ChownPlan9 version instead.
+	if runtime.GOOS == "windows" || runtime.GOOS == "plan9" {
+		return
+	}
+	// Use TempDir() to make sure we're on a local file system,
+	// so that the group ids returned by Getgroups will be allowed
+	// on the file.  On NFS, the Getgroups groups are
+	// basically useless.
+	f := newFile("TestChown", t)
+	defer Remove(f.Name())
+	defer f.Close()
+	dir, err := f.Stat()
+	if err != nil {
+		t.Fatalf("stat %s: %s", f.Name(), err)
+	}
+
+	// Can't change uid unless root, but can try
+	// changing the group id.  First try our current group.
+	gid := Getgid()
+	t.Log("gid:", gid)
+	if err = Chown(f.Name(), -1, gid); err != nil {
+		t.Fatalf("chown %s -1 %d: %s", f.Name(), gid, err)
+	}
+	sys := dir.Sys().(*syscall.Stat_t)
+	checkUidGid(t, f.Name(), int(sys.Uid), gid)
+
+	// Then try all the auxiliary groups.
+	groups, err := Getgroups()
+	if err != nil {
+		t.Fatalf("getgroups: %s", err)
+	}
+	t.Log("groups: ", groups)
+	for _, g := range groups {
+		if err = Chown(f.Name(), -1, g); err != nil {
+			t.Fatalf("chown %s -1 %d: %s", f.Name(), g, err)
+		}
+		checkUidGid(t, f.Name(), int(sys.Uid), g)
+
+		// change back to gid to test fd.Chown
+		if err = f.Chown(-1, gid); err != nil {
+			t.Fatalf("fchown %s -1 %d: %s", f.Name(), gid, err)
+		}
+		checkUidGid(t, f.Name(), int(sys.Uid), gid)
+	}
+}
diff --git a/src/os/os_windows_test.go b/src/os/os_windows_test.go
new file mode 100644
index 000000000..fd96713ea
--- /dev/null
+++ b/src/os/os_windows_test.go
@@ -0,0 +1,81 @@
+package os_test
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"syscall"
+	"testing"
+)
+
+func init() {
+	tmpdir, err := ioutil.TempDir("", "symtest")
+	if err != nil {
+		panic("failed to create temp directory: " + err.Error())
+	}
+	defer os.RemoveAll(tmpdir)
+
+	err = os.Symlink("target", filepath.Join(tmpdir, "symlink"))
+	if err == nil {
+		return
+	}
+
+	err = err.(*os.LinkError).Err
+	switch err {
+	case syscall.EWINDOWS, syscall.ERROR_PRIVILEGE_NOT_HELD:
+		supportsSymlinks = false
+	}
+}
+
+func TestSameWindowsFile(t *testing.T) {
+	temp, err := ioutil.TempDir("", "TestSameWindowsFile")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(temp)
+
+	wd, err := os.Getwd()
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = os.Chdir(temp)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.Chdir(wd)
+
+	f, err := os.Create("a")
+	if err != nil {
+		t.Fatal(err)
+	}
+	f.Close()
+
+	ia1, err := os.Stat("a")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	path, err := filepath.Abs("a")
+	if err != nil {
+		t.Fatal(err)
+	}
+	ia2, err := os.Stat(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !os.SameFile(ia1, ia2) {
+		t.Errorf("files should be same")
+	}
+
+	p := filepath.VolumeName(path) + filepath.Base(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	ia3, err := os.Stat(p)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !os.SameFile(ia1, ia3) {
+		t.Errorf("files should be same")
+	}
+}
diff --git a/src/os/path.go b/src/os/path.go
new file mode 100644
index 000000000..02a77ec80
--- /dev/null
+++ b/src/os/path.go
@@ -0,0 +1,123 @@
+// 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 (
+	"io"
+	"syscall"
+)
+
+// MkdirAll creates a directory named path,
+// along with any necessary parents, and returns nil,
+// or else returns an error.
+// The permission bits perm are used for all
+// directories that MkdirAll creates.
+// If path is already a directory, MkdirAll does nothing
+// and returns nil.
+func MkdirAll(path string, perm FileMode) error {
+	// If path exists, stop with success or error.
+	dir, err := Stat(path)
+	if err == nil {
+		if dir.IsDir() {
+			return nil
+		}
+		return &PathError{"mkdir", path, syscall.ENOTDIR}
+	}
+
+	// Doesn't already exist; make sure parent does.
+	i := len(path)
+	for i > 0 && IsPathSeparator(path[i-1]) { // Skip trailing path separator.
+		i--
+	}
+
+	j := i
+	for j > 0 && !IsPathSeparator(path[j-1]) { // Scan backward over element.
+		j--
+	}
+
+	if j > 1 {
+		// Create parent
+		err = MkdirAll(path[0:j-1], perm)
+		if err != nil {
+			return err
+		}
+	}
+
+	// Now parent exists, try to create.
+	err = Mkdir(path, perm)
+	if err != nil {
+		// Handle arguments like "foo/." by
+		// double-checking that directory doesn't exist.
+		dir, err1 := Lstat(path)
+		if err1 == nil && dir.IsDir() {
+			return nil
+		}
+		return err
+	}
+	return nil
+}
+
+// RemoveAll removes path and any children it contains.
+// It removes everything it can but returns the first error
+// it encounters.  If the path does not exist, RemoveAll
+// returns nil (no error).
+func RemoveAll(path string) error {
+	// Simple case: if Remove works, we're done.
+	err := Remove(path)
+	if err == nil {
+		return nil
+	}
+
+	// Otherwise, is this a directory we need to recurse into?
+	dir, serr := Lstat(path)
+	if serr != nil {
+		if serr, ok := serr.(*PathError); ok && (IsNotExist(serr.Err) || serr.Err == syscall.ENOTDIR) {
+			return nil
+		}
+		return serr
+	}
+	if !dir.IsDir() {
+		// Not a directory; return the error from Remove.
+		return err
+	}
+
+	// Directory.
+	fd, err := Open(path)
+	if err != nil {
+		return err
+	}
+
+	// Remove contents & return first error.
+	err = nil
+	for {
+		names, err1 := fd.Readdirnames(100)
+		for _, name := range names {
+			err1 := RemoveAll(path + string(PathSeparator) + name)
+			if err == nil {
+				err = err1
+			}
+		}
+		if err1 == io.EOF {
+			break
+		}
+		// If Readdirnames returned an error, use it.
+		if err == nil {
+			err = err1
+		}
+		if len(names) == 0 {
+			break
+		}
+	}
+
+	// Close directory, because windows won't remove opened directory.
+	fd.Close()
+
+	// Remove directory.
+	err1 := Remove(path)
+	if err == nil {
+		err = err1
+	}
+	return err
+}
diff --git a/src/os/path_plan9.go b/src/os/path_plan9.go
new file mode 100644
index 000000000..64bad500a
--- /dev/null
+++ b/src/os/path_plan9.go
@@ -0,0 +1,15 @@
+// Copyright 2011 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
+
+const (
+	PathSeparator     = '/'    // OS-specific path separator
+	PathListSeparator = '\000' // OS-specific path list separator
+)
+
+// IsPathSeparator returns true if c is a directory separator character.
+func IsPathSeparator(c uint8) bool {
+	return PathSeparator == c
+}
diff --git a/src/os/path_test.go b/src/os/path_test.go
new file mode 100644
index 000000000..6f24a4313
--- /dev/null
+++ b/src/os/path_test.go
@@ -0,0 +1,220 @@
+// 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_test
+
+import (
+	"io/ioutil"
+	. "os"
+	"path/filepath"
+	"runtime"
+	"syscall"
+	"testing"
+)
+
+func TestMkdirAll(t *testing.T) {
+	tmpDir := TempDir()
+	path := tmpDir + "/_TestMkdirAll_/dir/./dir2"
+	err := MkdirAll(path, 0777)
+	if err != nil {
+		t.Fatalf("MkdirAll %q: %s", path, err)
+	}
+	defer RemoveAll(tmpDir + "/_TestMkdirAll_")
+
+	// Already exists, should succeed.
+	err = MkdirAll(path, 0777)
+	if err != nil {
+		t.Fatalf("MkdirAll %q (second time): %s", path, err)
+	}
+
+	// Make file.
+	fpath := path + "/file"
+	f, err := Create(fpath)
+	if err != nil {
+		t.Fatalf("create %q: %s", fpath, err)
+	}
+	defer f.Close()
+
+	// Can't make directory named after file.
+	err = MkdirAll(fpath, 0777)
+	if err == nil {
+		t.Fatalf("MkdirAll %q: no error", fpath)
+	}
+	perr, ok := err.(*PathError)
+	if !ok {
+		t.Fatalf("MkdirAll %q returned %T, not *PathError", fpath, err)
+	}
+	if filepath.Clean(perr.Path) != filepath.Clean(fpath) {
+		t.Fatalf("MkdirAll %q returned wrong error path: %q not %q", fpath, filepath.Clean(perr.Path), filepath.Clean(fpath))
+	}
+
+	// Can't make subdirectory of file.
+	ffpath := fpath + "/subdir"
+	err = MkdirAll(ffpath, 0777)
+	if err == nil {
+		t.Fatalf("MkdirAll %q: no error", ffpath)
+	}
+	perr, ok = err.(*PathError)
+	if !ok {
+		t.Fatalf("MkdirAll %q returned %T, not *PathError", ffpath, err)
+	}
+	if filepath.Clean(perr.Path) != filepath.Clean(fpath) {
+		t.Fatalf("MkdirAll %q returned wrong error path: %q not %q", ffpath, filepath.Clean(perr.Path), filepath.Clean(fpath))
+	}
+
+	if runtime.GOOS == "windows" {
+		path := tmpDir + `\_TestMkdirAll_\dir\.\dir2\`
+		err := MkdirAll(path, 0777)
+		if err != nil {
+			t.Fatalf("MkdirAll %q: %s", path, err)
+		}
+	}
+}
+
+func TestRemoveAll(t *testing.T) {
+	tmpDir := TempDir()
+	// Work directory.
+	path := tmpDir + "/_TestRemoveAll_"
+	fpath := path + "/file"
+	dpath := path + "/dir"
+
+	// Make directory with 1 file and remove.
+	if err := MkdirAll(path, 0777); err != nil {
+		t.Fatalf("MkdirAll %q: %s", path, err)
+	}
+	fd, err := Create(fpath)
+	if err != nil {
+		t.Fatalf("create %q: %s", fpath, err)
+	}
+	fd.Close()
+	if err = RemoveAll(path); err != nil {
+		t.Fatalf("RemoveAll %q (first): %s", path, err)
+	}
+	if _, err = Lstat(path); err == nil {
+		t.Fatalf("Lstat %q succeeded after RemoveAll (first)", path)
+	}
+
+	// Make directory with file and subdirectory and remove.
+	if err = MkdirAll(dpath, 0777); err != nil {
+		t.Fatalf("MkdirAll %q: %s", dpath, err)
+	}
+	fd, err = Create(fpath)
+	if err != nil {
+		t.Fatalf("create %q: %s", fpath, err)
+	}
+	fd.Close()
+	fd, err = Create(dpath + "/file")
+	if err != nil {
+		t.Fatalf("create %q: %s", fpath, err)
+	}
+	fd.Close()
+	if err = RemoveAll(path); err != nil {
+		t.Fatalf("RemoveAll %q (second): %s", path, err)
+	}
+	if _, err := Lstat(path); err == nil {
+		t.Fatalf("Lstat %q succeeded after RemoveAll (second)", path)
+	}
+
+	// Determine if we should run the following test.
+	testit := true
+	if runtime.GOOS == "windows" {
+		// Chmod is not supported under windows.
+		testit = false
+	} else {
+		// Test fails as root.
+		testit = Getuid() != 0
+	}
+	if testit {
+		// Make directory with file and subdirectory and trigger error.
+		if err = MkdirAll(dpath, 0777); err != nil {
+			t.Fatalf("MkdirAll %q: %s", dpath, err)
+		}
+
+		for _, s := range []string{fpath, dpath + "/file1", path + "/zzz"} {
+			fd, err = Create(s)
+			if err != nil {
+				t.Fatalf("create %q: %s", s, err)
+			}
+			fd.Close()
+		}
+		if err = Chmod(dpath, 0); err != nil {
+			t.Fatalf("Chmod %q 0: %s", dpath, err)
+		}
+
+		// No error checking here: either RemoveAll
+		// will or won't be able to remove dpath;
+		// either way we want to see if it removes fpath
+		// and path/zzz.  Reasons why RemoveAll might
+		// succeed in removing dpath as well include:
+		//	* running as root
+		//	* running on a file system without permissions (FAT)
+		RemoveAll(path)
+		Chmod(dpath, 0777)
+
+		for _, s := range []string{fpath, path + "/zzz"} {
+			if _, err = Lstat(s); err == nil {
+				t.Fatalf("Lstat %q succeeded after partial RemoveAll", s)
+			}
+		}
+	}
+	if err = RemoveAll(path); err != nil {
+		t.Fatalf("RemoveAll %q after partial RemoveAll: %s", path, err)
+	}
+	if _, err = Lstat(path); err == nil {
+		t.Fatalf("Lstat %q succeeded after RemoveAll (final)", path)
+	}
+}
+
+func TestMkdirAllWithSymlink(t *testing.T) {
+	switch runtime.GOOS {
+	case "nacl", "plan9":
+		t.Skipf("skipping on %s", runtime.GOOS)
+	case "windows":
+		if !supportsSymlinks {
+			t.Skipf("skipping on %s", runtime.GOOS)
+		}
+	}
+
+	tmpDir, err := ioutil.TempDir("", "TestMkdirAllWithSymlink-")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer RemoveAll(tmpDir)
+
+	dir := tmpDir + "/dir"
+	err = Mkdir(dir, 0755)
+	if err != nil {
+		t.Fatalf("Mkdir %s: %s", dir, err)
+	}
+
+	link := tmpDir + "/link"
+	err = Symlink("dir", link)
+	if err != nil {
+		t.Fatalf("Symlink %s: %s", link, err)
+	}
+
+	path := link + "/foo"
+	err = MkdirAll(path, 0755)
+	if err != nil {
+		t.Errorf("MkdirAll %q: %s", path, err)
+	}
+}
+
+func TestMkdirAllAtSlash(t *testing.T) {
+	switch runtime.GOOS {
+	case "android", "plan9", "windows":
+		t.Skipf("skipping on %s", runtime.GOOS)
+	}
+	RemoveAll("/_go_os_test")
+	err := MkdirAll("/_go_os_test/dir", 0777)
+	if err != nil {
+		pathErr, ok := err.(*PathError)
+		// common for users not to be able to write to /
+		if ok && pathErr.Err == syscall.EACCES {
+			return
+		}
+		t.Fatalf(`MkdirAll "/_go_os_test/dir": %v`, err)
+	}
+	RemoveAll("/_go_os_test")
+}
diff --git a/src/os/path_unix.go b/src/os/path_unix.go
new file mode 100644
index 000000000..0211107dd
--- /dev/null
+++ b/src/os/path_unix.go
@@ -0,0 +1,17 @@
+// Copyright 2011 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.
+
+// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
+
+package os
+
+const (
+	PathSeparator     = '/' // OS-specific path separator
+	PathListSeparator = ':' // OS-specific path list separator
+)
+
+// IsPathSeparator returns true if c is a directory separator character.
+func IsPathSeparator(c uint8) bool {
+	return PathSeparator == c
+}
diff --git a/src/os/path_windows.go b/src/os/path_windows.go
new file mode 100644
index 000000000..61f2ca59f
--- /dev/null
+++ b/src/os/path_windows.go
@@ -0,0 +1,16 @@
+// Copyright 2011 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
+
+const (
+	PathSeparator     = '\\' // OS-specific path separator
+	PathListSeparator = ';'  // OS-specific path list separator
+)
+
+// IsPathSeparator returns true if c is a directory separator character.
+func IsPathSeparator(c uint8) bool {
+	// NOTE: Windows accept / as path separator.
+	return c == '\\' || c == '/'
+}
diff --git a/src/os/pipe_bsd.go b/src/os/pipe_bsd.go
new file mode 100644
index 000000000..3b81ed20f
--- /dev/null
+++ b/src/os/pipe_bsd.go
@@ -0,0 +1,28 @@
+// 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.
+
+// +build darwin dragonfly freebsd nacl netbsd openbsd solaris
+
+package os
+
+import "syscall"
+
+// Pipe returns a connected pair of Files; reads from r return bytes written to w.
+// It returns the files and an error, if any.
+func Pipe() (r *File, w *File, err error) {
+	var p [2]int
+
+	// See ../syscall/exec.go for description of lock.
+	syscall.ForkLock.RLock()
+	e := syscall.Pipe(p[0:])
+	if e != nil {
+		syscall.ForkLock.RUnlock()
+		return nil, nil, NewSyscallError("pipe", e)
+	}
+	syscall.CloseOnExec(p[0])
+	syscall.CloseOnExec(p[1])
+	syscall.ForkLock.RUnlock()
+
+	return NewFile(uintptr(p[0]), "|0"), NewFile(uintptr(p[1]), "|1"), nil
+}
diff --git a/src/os/pipe_linux.go b/src/os/pipe_linux.go
new file mode 100644
index 000000000..9bafad84f
--- /dev/null
+++ b/src/os/pipe_linux.go
@@ -0,0 +1,33 @@
+// Copyright 2013 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 "syscall"
+
+// Pipe returns a connected pair of Files; reads from r return bytes written to w.
+// It returns the files and an error, if any.
+func Pipe() (r *File, w *File, err error) {
+	var p [2]int
+
+	e := syscall.Pipe2(p[0:], syscall.O_CLOEXEC)
+	// pipe2 was added in 2.6.27 and our minimum requirement is 2.6.23, so it
+	// might not be implemented.
+	if e == syscall.ENOSYS {
+		// See ../syscall/exec.go for description of lock.
+		syscall.ForkLock.RLock()
+		e = syscall.Pipe(p[0:])
+		if e != nil {
+			syscall.ForkLock.RUnlock()
+			return nil, nil, NewSyscallError("pipe", e)
+		}
+		syscall.CloseOnExec(p[0])
+		syscall.CloseOnExec(p[1])
+		syscall.ForkLock.RUnlock()
+	} else if e != nil {
+		return nil, nil, NewSyscallError("pipe2", e)
+	}
+
+	return NewFile(uintptr(p[0]), "|0"), NewFile(uintptr(p[1]), "|1"), nil
+}
diff --git a/src/os/proc.go b/src/os/proc.go
new file mode 100644
index 000000000..38c436ec5
--- /dev/null
+++ b/src/os/proc.go
@@ -0,0 +1,36 @@
+// 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.
+
+// Process etc.
+
+package os
+
+import "syscall"
+
+// Args hold the command-line arguments, starting with the program name.
+var Args []string
+
+// Getuid returns the numeric user id of the caller.
+func Getuid() int { return syscall.Getuid() }
+
+// Geteuid returns the numeric effective user id of the caller.
+func Geteuid() int { return syscall.Geteuid() }
+
+// Getgid returns the numeric group id of the caller.
+func Getgid() int { return syscall.Getgid() }
+
+// Getegid returns the numeric effective group id of the caller.
+func Getegid() int { return syscall.Getegid() }
+
+// Getgroups returns a list of the numeric ids of groups that the caller belongs to.
+func Getgroups() ([]int, error) {
+	gids, e := syscall.Getgroups()
+	return gids, NewSyscallError("getgroups", e)
+}
+
+// Exit causes the current program to exit with the given status code.
+// Conventionally, code zero indicates success, non-zero an error.
+// The program terminates immediately; deferred functions are
+// not run.
+func Exit(code int) { syscall.Exit(code) }
diff --git a/src/os/signal/example_test.go b/src/os/signal/example_test.go
new file mode 100644
index 000000000..079ee5070
--- /dev/null
+++ b/src/os/signal/example_test.go
@@ -0,0 +1,23 @@
+// Copyright 2013 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 signal_test
+
+import (
+	"fmt"
+	"os"
+	"os/signal"
+)
+
+func ExampleNotify() {
+	// Set up channel on which to send signal notifications.
+	// We must use a buffered channel or risk missing the signal
+	// if we're not ready to receive when the signal is sent.
+	c := make(chan os.Signal, 1)
+	signal.Notify(c, os.Interrupt, os.Kill)
+
+	// Block until a signal is received.
+	s := <-c
+	fmt.Println("Got signal:", s)
+}
diff --git a/src/os/signal/sig.s b/src/os/signal/sig.s
new file mode 100644
index 000000000..d54c284b5
--- /dev/null
+++ b/src/os/signal/sig.s
@@ -0,0 +1,23 @@
+// Copyright 2012 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.
+
+// Assembly to get into package runtime without using exported symbols.
+
+// +build amd64 amd64p32 arm 386
+
+#include "textflag.h"
+
+#ifdef GOARCH_arm
+#define JMP B
+#endif
+
+TEXT ·signal_disable(SB),NOSPLIT,$0
+	JMP runtime·signal_disable(SB)
+
+TEXT ·signal_enable(SB),NOSPLIT,$0
+	JMP runtime·signal_enable(SB)
+
+TEXT ·signal_recv(SB),NOSPLIT,$0
+	JMP runtime·signal_recv(SB)
+
diff --git a/src/os/signal/signal.go b/src/os/signal/signal.go
new file mode 100644
index 000000000..300427549
--- /dev/null
+++ b/src/os/signal/signal.go
@@ -0,0 +1,131 @@
+// Copyright 2012 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 signal implements access to incoming signals.
+package signal
+
+// BUG(rsc): This package is not yet implemented on Plan 9.
+
+import (
+	"os"
+	"sync"
+)
+
+var handlers struct {
+	sync.Mutex
+	m   map[chan<- os.Signal]*handler
+	ref [numSig]int64
+}
+
+type handler struct {
+	mask [(numSig + 31) / 32]uint32
+}
+
+func (h *handler) want(sig int) bool {
+	return (h.mask[sig/32]>>uint(sig&31))&1 != 0
+}
+
+func (h *handler) set(sig int) {
+	h.mask[sig/32] |= 1 << uint(sig&31)
+}
+
+// Notify causes package signal to relay incoming signals to c.
+// If no signals are listed, all incoming signals will be relayed to c.
+// Otherwise, just the listed signals will.
+//
+// Package signal will not block sending to c: the caller must ensure
+// that c has sufficient buffer space to keep up with the expected
+// signal rate.  For a channel used for notification of just one signal value,
+// a buffer of size 1 is sufficient.
+//
+// It is allowed to call Notify multiple times with the same channel:
+// each call expands the set of signals sent to that channel.
+// The only way to remove signals from the set is to call Stop.
+//
+// It is allowed to call Notify multiple times with different channels
+// and the same signals: each channel receives copies of incoming
+// signals independently.
+func Notify(c chan<- os.Signal, sig ...os.Signal) {
+	if c == nil {
+		panic("os/signal: Notify using nil channel")
+	}
+
+	handlers.Lock()
+	defer handlers.Unlock()
+
+	h := handlers.m[c]
+	if h == nil {
+		if handlers.m == nil {
+			handlers.m = make(map[chan<- os.Signal]*handler)
+		}
+		h = new(handler)
+		handlers.m[c] = h
+	}
+
+	add := func(n int) {
+		if n < 0 {
+			return
+		}
+		if !h.want(n) {
+			h.set(n)
+			if handlers.ref[n] == 0 {
+				enableSignal(n)
+			}
+			handlers.ref[n]++
+		}
+	}
+
+	if len(sig) == 0 {
+		for n := 0; n < numSig; n++ {
+			add(n)
+		}
+	} else {
+		for _, s := range sig {
+			add(signum(s))
+		}
+	}
+}
+
+// Stop causes package signal to stop relaying incoming signals to c.
+// It undoes the effect of all prior calls to Notify using c.
+// When Stop returns, it is guaranteed that c will receive no more signals.
+func Stop(c chan<- os.Signal) {
+	handlers.Lock()
+	defer handlers.Unlock()
+
+	h := handlers.m[c]
+	if h == nil {
+		return
+	}
+	delete(handlers.m, c)
+
+	for n := 0; n < numSig; n++ {
+		if h.want(n) {
+			handlers.ref[n]--
+			if handlers.ref[n] == 0 {
+				disableSignal(n)
+			}
+		}
+	}
+}
+
+func process(sig os.Signal) {
+	n := signum(sig)
+	if n < 0 {
+		return
+	}
+
+	handlers.Lock()
+	defer handlers.Unlock()
+
+	for c, h := range handlers.m {
+		if h.want(n) {
+			// send but do not block for it
+			select {
+			case c <- sig:
+			default:
+			}
+		}
+	}
+}
diff --git a/src/os/signal/signal_stub.go b/src/os/signal/signal_stub.go
new file mode 100644
index 000000000..d0a6935ff
--- /dev/null
+++ b/src/os/signal/signal_stub.go
@@ -0,0 +1,17 @@
+// Copyright 2012 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.
+
+// +build plan9
+
+package signal
+
+import "os"
+
+const numSig = 0
+
+func signum(sig os.Signal) int { return -1 }
+
+func disableSignal(int) {}
+
+func enableSignal(int) {}
diff --git a/src/os/signal/signal_test.go b/src/os/signal/signal_test.go
new file mode 100644
index 000000000..076fe3f93
--- /dev/null
+++ b/src/os/signal/signal_test.go
@@ -0,0 +1,208 @@
+// 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.
+
+// +build darwin dragonfly freebsd linux netbsd openbsd solaris
+
+package signal
+
+import (
+	"flag"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"runtime"
+	"strconv"
+	"syscall"
+	"testing"
+	"time"
+)
+
+func waitSig(t *testing.T, c <-chan os.Signal, sig os.Signal) {
+	select {
+	case s := <-c:
+		if s != sig {
+			t.Fatalf("signal was %v, want %v", s, sig)
+		}
+	case <-time.After(1 * time.Second):
+		t.Fatalf("timeout waiting for %v", sig)
+	}
+}
+
+// Test that basic signal handling works.
+func TestSignal(t *testing.T) {
+	// Ask for SIGHUP
+	c := make(chan os.Signal, 1)
+	Notify(c, syscall.SIGHUP)
+	defer Stop(c)
+
+	// Send this process a SIGHUP
+	t.Logf("sighup...")
+	syscall.Kill(syscall.Getpid(), syscall.SIGHUP)
+	waitSig(t, c, syscall.SIGHUP)
+
+	// Ask for everything we can get.
+	c1 := make(chan os.Signal, 1)
+	Notify(c1)
+
+	// Send this process a SIGWINCH
+	t.Logf("sigwinch...")
+	syscall.Kill(syscall.Getpid(), syscall.SIGWINCH)
+	waitSig(t, c1, syscall.SIGWINCH)
+
+	// Send two more SIGHUPs, to make sure that
+	// they get delivered on c1 and that not reading
+	// from c does not block everything.
+	t.Logf("sighup...")
+	syscall.Kill(syscall.Getpid(), syscall.SIGHUP)
+	waitSig(t, c1, syscall.SIGHUP)
+	t.Logf("sighup...")
+	syscall.Kill(syscall.Getpid(), syscall.SIGHUP)
+	waitSig(t, c1, syscall.SIGHUP)
+
+	// The first SIGHUP should be waiting for us on c.
+	waitSig(t, c, syscall.SIGHUP)
+}
+
+func TestStress(t *testing.T) {
+	dur := 3 * time.Second
+	if testing.Short() {
+		dur = 100 * time.Millisecond
+	}
+	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(4))
+	done := make(chan bool)
+	finished := make(chan bool)
+	go func() {
+		sig := make(chan os.Signal, 1)
+		Notify(sig, syscall.SIGUSR1)
+		defer Stop(sig)
+	Loop:
+		for {
+			select {
+			case <-sig:
+			case <-done:
+				break Loop
+			}
+		}
+		finished <- true
+	}()
+	go func() {
+	Loop:
+		for {
+			select {
+			case <-done:
+				break Loop
+			default:
+				syscall.Kill(syscall.Getpid(), syscall.SIGUSR1)
+				runtime.Gosched()
+			}
+		}
+		finished <- true
+	}()
+	time.Sleep(dur)
+	close(done)
+	<-finished
+	<-finished
+	// When run with 'go test -cpu=1,2,4' SIGUSR1 from this test can slip
+	// into subsequent TestSignal() causing failure.
+	// Sleep for a while to reduce the possibility of the failure.
+	time.Sleep(10 * time.Millisecond)
+}
+
+var sendUncaughtSighup = flag.Int("send_uncaught_sighup", 0, "send uncaught SIGHUP during TestStop")
+
+// Test that Stop cancels the channel's registrations.
+func TestStop(t *testing.T) {
+	sigs := []syscall.Signal{
+		syscall.SIGWINCH,
+		syscall.SIGHUP,
+	}
+
+	for _, sig := range sigs {
+		// Send the signal.
+		// If it's SIGWINCH, we should not see it.
+		// If it's SIGHUP, maybe we'll die. Let the flag tell us what to do.
+		if sig != syscall.SIGHUP || *sendUncaughtSighup == 1 {
+			syscall.Kill(syscall.Getpid(), sig)
+		}
+		time.Sleep(10 * time.Millisecond)
+
+		// Ask for signal
+		c := make(chan os.Signal, 1)
+		Notify(c, sig)
+		defer Stop(c)
+
+		// Send this process that signal
+		syscall.Kill(syscall.Getpid(), sig)
+		waitSig(t, c, sig)
+
+		Stop(c)
+		select {
+		case s := <-c:
+			t.Fatalf("unexpected signal %v", s)
+		case <-time.After(10 * time.Millisecond):
+			// nothing to read - good
+		}
+
+		// Send the signal.
+		// If it's SIGWINCH, we should not see it.
+		// If it's SIGHUP, maybe we'll die. Let the flag tell us what to do.
+		if sig != syscall.SIGHUP || *sendUncaughtSighup == 2 {
+			syscall.Kill(syscall.Getpid(), sig)
+		}
+
+		select {
+		case s := <-c:
+			t.Fatalf("unexpected signal %v", s)
+		case <-time.After(10 * time.Millisecond):
+			// nothing to read - good
+		}
+	}
+}
+
+// Test that when run under nohup, an uncaught SIGHUP does not kill the program,
+// but a
+func TestNohup(t *testing.T) {
+	// Ugly: ask for SIGHUP so that child will not have no-hup set
+	// even if test is running under nohup environment.
+	// We have no intention of reading from c.
+	c := make(chan os.Signal, 1)
+	Notify(c, syscall.SIGHUP)
+
+	// When run without nohup, the test should crash on an uncaught SIGHUP.
+	// When run under nohup, the test should ignore uncaught SIGHUPs,
+	// because the runtime is not supposed to be listening for them.
+	// Either way, TestStop should still be able to catch them when it wants them
+	// and then when it stops wanting them, the original behavior should resume.
+	//
+	// send_uncaught_sighup=1 sends the SIGHUP before starting to listen for SIGHUPs.
+	// send_uncaught_sighup=2 sends the SIGHUP after no longer listening for SIGHUPs.
+	//
+	// Both should fail without nohup and succeed with nohup.
+
+	for i := 1; i <= 2; i++ {
+		out, err := exec.Command(os.Args[0], "-test.run=TestStop", "-send_uncaught_sighup="+strconv.Itoa(i)).CombinedOutput()
+		if err == nil {
+			t.Fatalf("ran test with -send_uncaught_sighup=%d and it succeeded: expected failure.\nOutput:\n%s", i, out)
+		}
+	}
+
+	Stop(c)
+
+	// Again, this time with nohup, assuming we can find it.
+	_, err := os.Stat("/usr/bin/nohup")
+	if err != nil {
+		t.Skip("cannot find nohup; skipping second half of test")
+	}
+
+	for i := 1; i <= 2; i++ {
+		os.Remove("nohup.out")
+		out, err := exec.Command("/usr/bin/nohup", os.Args[0], "-test.run=TestStop", "-send_uncaught_sighup="+strconv.Itoa(i)).CombinedOutput()
+
+		data, _ := ioutil.ReadFile("nohup.out")
+		os.Remove("nohup.out")
+		if err != nil {
+			t.Fatalf("ran test with -send_uncaught_sighup=%d under nohup and it failed: expected success.\nError: %v\nOutput:\n%s%s", i, err, out, data)
+		}
+	}
+}
diff --git a/src/os/signal/signal_unix.go b/src/os/signal/signal_unix.go
new file mode 100644
index 000000000..94b8ab3dd
--- /dev/null
+++ b/src/os/signal/signal_unix.go
@@ -0,0 +1,53 @@
+// Copyright 2012 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.
+
+// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris windows
+
+package signal
+
+import (
+	"os"
+	"syscall"
+)
+
+// In assembly.
+func signal_disable(uint32)
+func signal_enable(uint32)
+func signal_recv() uint32
+
+func loop() {
+	for {
+		process(syscall.Signal(signal_recv()))
+	}
+}
+
+func init() {
+	signal_enable(0) // first call - initialize
+	go loop()
+}
+
+const (
+	numSig = 65 // max across all systems
+)
+
+func signum(sig os.Signal) int {
+	switch sig := sig.(type) {
+	case syscall.Signal:
+		i := int(sig)
+		if i < 0 || i >= numSig {
+			return -1
+		}
+		return i
+	default:
+		return -1
+	}
+}
+
+func enableSignal(sig int) {
+	signal_enable(uint32(sig))
+}
+
+func disableSignal(sig int) {
+	signal_disable(uint32(sig))
+}
diff --git a/src/os/signal/signal_windows_test.go b/src/os/signal/signal_windows_test.go
new file mode 100644
index 000000000..f3e6706b7
--- /dev/null
+++ b/src/os/signal/signal_windows_test.go
@@ -0,0 +1,103 @@
+// Copyright 2012 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 signal
+
+import (
+	"bytes"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"syscall"
+	"testing"
+	"time"
+)
+
+func sendCtrlBreak(t *testing.T, pid int) {
+	d, e := syscall.LoadDLL("kernel32.dll")
+	if e != nil {
+		t.Fatalf("LoadDLL: %v\n", e)
+	}
+	p, e := d.FindProc("GenerateConsoleCtrlEvent")
+	if e != nil {
+		t.Fatalf("FindProc: %v\n", e)
+	}
+	r, _, e := p.Call(syscall.CTRL_BREAK_EVENT, uintptr(pid))
+	if r == 0 {
+		t.Fatalf("GenerateConsoleCtrlEvent: %v\n", e)
+	}
+}
+
+func TestCtrlBreak(t *testing.T) {
+	// create source file
+	const source = `
+package main
+
+import (
+	"log"
+	"os"
+	"os/signal"
+	"time"
+)
+
+
+func main() {
+	c := make(chan os.Signal, 10)
+	signal.Notify(c)
+	select {
+	case s := <-c:
+		if s != os.Interrupt {
+			log.Fatalf("Wrong signal received: got %q, want %q\n", s, os.Interrupt)
+		}
+	case <-time.After(3 * time.Second):
+		log.Fatalf("Timeout waiting for Ctrl+Break\n")
+	}
+}
+`
+	tmp, err := ioutil.TempDir("", "TestCtrlBreak")
+	if err != nil {
+		t.Fatal("TempDir failed: ", err)
+	}
+	defer os.RemoveAll(tmp)
+
+	// write ctrlbreak.go
+	name := filepath.Join(tmp, "ctlbreak")
+	src := name + ".go"
+	f, err := os.Create(src)
+	if err != nil {
+		t.Fatalf("Failed to create %v: %v", src, err)
+	}
+	defer f.Close()
+	f.Write([]byte(source))
+
+	// compile it
+	exe := name + ".exe"
+	defer os.Remove(exe)
+	o, err := exec.Command("go", "build", "-o", exe, src).CombinedOutput()
+	if err != nil {
+		t.Fatalf("Failed to compile: %v\n%v", err, string(o))
+	}
+
+	// run it
+	cmd := exec.Command(exe)
+	var b bytes.Buffer
+	cmd.Stdout = &b
+	cmd.Stderr = &b
+	cmd.SysProcAttr = &syscall.SysProcAttr{
+		CreationFlags: syscall.CREATE_NEW_PROCESS_GROUP,
+	}
+	err = cmd.Start()
+	if err != nil {
+		t.Fatalf("Start failed: %v", err)
+	}
+	go func() {
+		time.Sleep(1 * time.Second)
+		sendCtrlBreak(t, cmd.Process.Pid)
+	}()
+	err = cmd.Wait()
+	if err != nil {
+		t.Fatalf("Program exited with error: %v\n%v", err, string(b.Bytes()))
+	}
+}
diff --git a/src/os/stat_darwin.go b/src/os/stat_darwin.go
new file mode 100644
index 000000000..0eea52201
--- /dev/null
+++ b/src/os/stat_darwin.go
@@ -0,0 +1,61 @@
+// 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 (
+	"syscall"
+	"time"
+)
+
+func sameFile(fs1, fs2 *fileStat) bool {
+	stat1 := fs1.sys.(*syscall.Stat_t)
+	stat2 := fs2.sys.(*syscall.Stat_t)
+	return stat1.Dev == stat2.Dev && stat1.Ino == stat2.Ino
+}
+
+func fileInfoFromStat(st *syscall.Stat_t, name string) FileInfo {
+	fs := &fileStat{
+		name:    basename(name),
+		size:    int64(st.Size),
+		modTime: timespecToTime(st.Mtimespec),
+		sys:     st,
+	}
+	fs.mode = FileMode(st.Mode & 0777)
+	switch st.Mode & syscall.S_IFMT {
+	case syscall.S_IFBLK, syscall.S_IFWHT:
+		fs.mode |= ModeDevice
+	case syscall.S_IFCHR:
+		fs.mode |= ModeDevice | ModeCharDevice
+	case syscall.S_IFDIR:
+		fs.mode |= ModeDir
+	case syscall.S_IFIFO:
+		fs.mode |= ModeNamedPipe
+	case syscall.S_IFLNK:
+		fs.mode |= ModeSymlink
+	case syscall.S_IFREG:
+		// nothing to do
+	case syscall.S_IFSOCK:
+		fs.mode |= ModeSocket
+	}
+	if st.Mode&syscall.S_ISGID != 0 {
+		fs.mode |= ModeSetgid
+	}
+	if st.Mode&syscall.S_ISUID != 0 {
+		fs.mode |= ModeSetuid
+	}
+	if st.Mode&syscall.S_ISVTX != 0 {
+		fs.mode |= ModeSticky
+	}
+	return fs
+}
+
+func timespecToTime(ts syscall.Timespec) time.Time {
+	return time.Unix(int64(ts.Sec), int64(ts.Nsec))
+}
+
+// For testing.
+func atime(fi FileInfo) time.Time {
+	return timespecToTime(fi.Sys().(*syscall.Stat_t).Atimespec)
+}
diff --git a/src/os/stat_dragonfly.go b/src/os/stat_dragonfly.go
new file mode 100644
index 000000000..605c1d9b6
--- /dev/null
+++ b/src/os/stat_dragonfly.go
@@ -0,0 +1,61 @@
+// 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 (
+	"syscall"
+	"time"
+)
+
+func sameFile(fs1, fs2 *fileStat) bool {
+	stat1 := fs1.sys.(*syscall.Stat_t)
+	stat2 := fs2.sys.(*syscall.Stat_t)
+	return stat1.Dev == stat2.Dev && stat1.Ino == stat2.Ino
+}
+
+func fileInfoFromStat(st *syscall.Stat_t, name string) FileInfo {
+	fs := &fileStat{
+		name:    basename(name),
+		size:    int64(st.Size),
+		modTime: timespecToTime(st.Mtim),
+		sys:     st,
+	}
+	fs.mode = FileMode(st.Mode & 0777)
+	switch st.Mode & syscall.S_IFMT {
+	case syscall.S_IFBLK:
+		fs.mode |= ModeDevice
+	case syscall.S_IFCHR:
+		fs.mode |= ModeDevice | ModeCharDevice
+	case syscall.S_IFDIR:
+		fs.mode |= ModeDir
+	case syscall.S_IFIFO:
+		fs.mode |= ModeNamedPipe
+	case syscall.S_IFLNK:
+		fs.mode |= ModeSymlink
+	case syscall.S_IFREG:
+		// nothing to do
+	case syscall.S_IFSOCK:
+		fs.mode |= ModeSocket
+	}
+	if st.Mode&syscall.S_ISGID != 0 {
+		fs.mode |= ModeSetgid
+	}
+	if st.Mode&syscall.S_ISUID != 0 {
+		fs.mode |= ModeSetuid
+	}
+	if st.Mode&syscall.S_ISVTX != 0 {
+		fs.mode |= ModeSticky
+	}
+	return fs
+}
+
+func timespecToTime(ts syscall.Timespec) time.Time {
+	return time.Unix(int64(ts.Sec), int64(ts.Nsec))
+}
+
+// For testing.
+func atime(fi FileInfo) time.Time {
+	return timespecToTime(fi.Sys().(*syscall.Stat_t).Atim)
+}
diff --git a/src/os/stat_freebsd.go b/src/os/stat_freebsd.go
new file mode 100644
index 000000000..2ffb60fe2
--- /dev/null
+++ b/src/os/stat_freebsd.go
@@ -0,0 +1,61 @@
+// 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 (
+	"syscall"
+	"time"
+)
+
+func sameFile(fs1, fs2 *fileStat) bool {
+	stat1 := fs1.sys.(*syscall.Stat_t)
+	stat2 := fs2.sys.(*syscall.Stat_t)
+	return stat1.Dev == stat2.Dev && stat1.Ino == stat2.Ino
+}
+
+func fileInfoFromStat(st *syscall.Stat_t, name string) FileInfo {
+	fs := &fileStat{
+		name:    basename(name),
+		size:    int64(st.Size),
+		modTime: timespecToTime(st.Mtimespec),
+		sys:     st,
+	}
+	fs.mode = FileMode(st.Mode & 0777)
+	switch st.Mode & syscall.S_IFMT {
+	case syscall.S_IFBLK:
+		fs.mode |= ModeDevice
+	case syscall.S_IFCHR:
+		fs.mode |= ModeDevice | ModeCharDevice
+	case syscall.S_IFDIR:
+		fs.mode |= ModeDir
+	case syscall.S_IFIFO:
+		fs.mode |= ModeNamedPipe
+	case syscall.S_IFLNK:
+		fs.mode |= ModeSymlink
+	case syscall.S_IFREG:
+		// nothing to do
+	case syscall.S_IFSOCK:
+		fs.mode |= ModeSocket
+	}
+	if st.Mode&syscall.S_ISGID != 0 {
+		fs.mode |= ModeSetgid
+	}
+	if st.Mode&syscall.S_ISUID != 0 {
+		fs.mode |= ModeSetuid
+	}
+	if st.Mode&syscall.S_ISVTX != 0 {
+		fs.mode |= ModeSticky
+	}
+	return fs
+}
+
+func timespecToTime(ts syscall.Timespec) time.Time {
+	return time.Unix(int64(ts.Sec), int64(ts.Nsec))
+}
+
+// For testing.
+func atime(fi FileInfo) time.Time {
+	return timespecToTime(fi.Sys().(*syscall.Stat_t).Atimespec)
+}
diff --git a/src/os/stat_linux.go b/src/os/stat_linux.go
new file mode 100644
index 000000000..605c1d9b6
--- /dev/null
+++ b/src/os/stat_linux.go
@@ -0,0 +1,61 @@
+// 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 (
+	"syscall"
+	"time"
+)
+
+func sameFile(fs1, fs2 *fileStat) bool {
+	stat1 := fs1.sys.(*syscall.Stat_t)
+	stat2 := fs2.sys.(*syscall.Stat_t)
+	return stat1.Dev == stat2.Dev && stat1.Ino == stat2.Ino
+}
+
+func fileInfoFromStat(st *syscall.Stat_t, name string) FileInfo {
+	fs := &fileStat{
+		name:    basename(name),
+		size:    int64(st.Size),
+		modTime: timespecToTime(st.Mtim),
+		sys:     st,
+	}
+	fs.mode = FileMode(st.Mode & 0777)
+	switch st.Mode & syscall.S_IFMT {
+	case syscall.S_IFBLK:
+		fs.mode |= ModeDevice
+	case syscall.S_IFCHR:
+		fs.mode |= ModeDevice | ModeCharDevice
+	case syscall.S_IFDIR:
+		fs.mode |= ModeDir
+	case syscall.S_IFIFO:
+		fs.mode |= ModeNamedPipe
+	case syscall.S_IFLNK:
+		fs.mode |= ModeSymlink
+	case syscall.S_IFREG:
+		// nothing to do
+	case syscall.S_IFSOCK:
+		fs.mode |= ModeSocket
+	}
+	if st.Mode&syscall.S_ISGID != 0 {
+		fs.mode |= ModeSetgid
+	}
+	if st.Mode&syscall.S_ISUID != 0 {
+		fs.mode |= ModeSetuid
+	}
+	if st.Mode&syscall.S_ISVTX != 0 {
+		fs.mode |= ModeSticky
+	}
+	return fs
+}
+
+func timespecToTime(ts syscall.Timespec) time.Time {
+	return time.Unix(int64(ts.Sec), int64(ts.Nsec))
+}
+
+// For testing.
+func atime(fi FileInfo) time.Time {
+	return timespecToTime(fi.Sys().(*syscall.Stat_t).Atim)
+}
diff --git a/src/os/stat_nacl.go b/src/os/stat_nacl.go
new file mode 100644
index 000000000..a503b59fa
--- /dev/null
+++ b/src/os/stat_nacl.go
@@ -0,0 +1,62 @@
+// 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 (
+	"syscall"
+	"time"
+)
+
+func sameFile(fs1, fs2 *fileStat) bool {
+	stat1 := fs1.sys.(*syscall.Stat_t)
+	stat2 := fs2.sys.(*syscall.Stat_t)
+	return stat1.Dev == stat2.Dev && stat1.Ino == stat2.Ino
+}
+
+func fileInfoFromStat(st *syscall.Stat_t, name string) FileInfo {
+	fs := &fileStat{
+		name:    basename(name),
+		size:    int64(st.Size),
+		modTime: timespecToTime(st.Mtime, st.MtimeNsec),
+		sys:     st,
+	}
+	fs.mode = FileMode(st.Mode & 0777)
+	switch st.Mode & syscall.S_IFMT {
+	case syscall.S_IFBLK:
+		fs.mode |= ModeDevice
+	case syscall.S_IFCHR:
+		fs.mode |= ModeDevice | ModeCharDevice
+	case syscall.S_IFDIR:
+		fs.mode |= ModeDir
+	case syscall.S_IFIFO:
+		fs.mode |= ModeNamedPipe
+	case syscall.S_IFLNK:
+		fs.mode |= ModeSymlink
+	case syscall.S_IFREG:
+		// nothing to do
+	case syscall.S_IFSOCK:
+		fs.mode |= ModeSocket
+	}
+	if st.Mode&syscall.S_ISGID != 0 {
+		fs.mode |= ModeSetgid
+	}
+	if st.Mode&syscall.S_ISUID != 0 {
+		fs.mode |= ModeSetuid
+	}
+	if st.Mode&syscall.S_ISVTX != 0 {
+		fs.mode |= ModeSticky
+	}
+	return fs
+}
+
+func timespecToTime(sec, nsec int64) time.Time {
+	return time.Unix(sec, nsec)
+}
+
+// For testing.
+func atime(fi FileInfo) time.Time {
+	st := fi.Sys().(*syscall.Stat_t)
+	return timespecToTime(st.Atime, st.AtimeNsec)
+}
diff --git a/src/os/stat_netbsd.go b/src/os/stat_netbsd.go
new file mode 100644
index 000000000..2ffb60fe2
--- /dev/null
+++ b/src/os/stat_netbsd.go
@@ -0,0 +1,61 @@
+// 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 (
+	"syscall"
+	"time"
+)
+
+func sameFile(fs1, fs2 *fileStat) bool {
+	stat1 := fs1.sys.(*syscall.Stat_t)
+	stat2 := fs2.sys.(*syscall.Stat_t)
+	return stat1.Dev == stat2.Dev && stat1.Ino == stat2.Ino
+}
+
+func fileInfoFromStat(st *syscall.Stat_t, name string) FileInfo {
+	fs := &fileStat{
+		name:    basename(name),
+		size:    int64(st.Size),
+		modTime: timespecToTime(st.Mtimespec),
+		sys:     st,
+	}
+	fs.mode = FileMode(st.Mode & 0777)
+	switch st.Mode & syscall.S_IFMT {
+	case syscall.S_IFBLK:
+		fs.mode |= ModeDevice
+	case syscall.S_IFCHR:
+		fs.mode |= ModeDevice | ModeCharDevice
+	case syscall.S_IFDIR:
+		fs.mode |= ModeDir
+	case syscall.S_IFIFO:
+		fs.mode |= ModeNamedPipe
+	case syscall.S_IFLNK:
+		fs.mode |= ModeSymlink
+	case syscall.S_IFREG:
+		// nothing to do
+	case syscall.S_IFSOCK:
+		fs.mode |= ModeSocket
+	}
+	if st.Mode&syscall.S_ISGID != 0 {
+		fs.mode |= ModeSetgid
+	}
+	if st.Mode&syscall.S_ISUID != 0 {
+		fs.mode |= ModeSetuid
+	}
+	if st.Mode&syscall.S_ISVTX != 0 {
+		fs.mode |= ModeSticky
+	}
+	return fs
+}
+
+func timespecToTime(ts syscall.Timespec) time.Time {
+	return time.Unix(int64(ts.Sec), int64(ts.Nsec))
+}
+
+// For testing.
+func atime(fi FileInfo) time.Time {
+	return timespecToTime(fi.Sys().(*syscall.Stat_t).Atimespec)
+}
diff --git a/src/os/stat_openbsd.go b/src/os/stat_openbsd.go
new file mode 100644
index 000000000..605c1d9b6
--- /dev/null
+++ b/src/os/stat_openbsd.go
@@ -0,0 +1,61 @@
+// 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 (
+	"syscall"
+	"time"
+)
+
+func sameFile(fs1, fs2 *fileStat) bool {
+	stat1 := fs1.sys.(*syscall.Stat_t)
+	stat2 := fs2.sys.(*syscall.Stat_t)
+	return stat1.Dev == stat2.Dev && stat1.Ino == stat2.Ino
+}
+
+func fileInfoFromStat(st *syscall.Stat_t, name string) FileInfo {
+	fs := &fileStat{
+		name:    basename(name),
+		size:    int64(st.Size),
+		modTime: timespecToTime(st.Mtim),
+		sys:     st,
+	}
+	fs.mode = FileMode(st.Mode & 0777)
+	switch st.Mode & syscall.S_IFMT {
+	case syscall.S_IFBLK:
+		fs.mode |= ModeDevice
+	case syscall.S_IFCHR:
+		fs.mode |= ModeDevice | ModeCharDevice
+	case syscall.S_IFDIR:
+		fs.mode |= ModeDir
+	case syscall.S_IFIFO:
+		fs.mode |= ModeNamedPipe
+	case syscall.S_IFLNK:
+		fs.mode |= ModeSymlink
+	case syscall.S_IFREG:
+		// nothing to do
+	case syscall.S_IFSOCK:
+		fs.mode |= ModeSocket
+	}
+	if st.Mode&syscall.S_ISGID != 0 {
+		fs.mode |= ModeSetgid
+	}
+	if st.Mode&syscall.S_ISUID != 0 {
+		fs.mode |= ModeSetuid
+	}
+	if st.Mode&syscall.S_ISVTX != 0 {
+		fs.mode |= ModeSticky
+	}
+	return fs
+}
+
+func timespecToTime(ts syscall.Timespec) time.Time {
+	return time.Unix(int64(ts.Sec), int64(ts.Nsec))
+}
+
+// For testing.
+func atime(fi FileInfo) time.Time {
+	return timespecToTime(fi.Sys().(*syscall.Stat_t).Atim)
+}
diff --git a/src/os/stat_plan9.go b/src/os/stat_plan9.go
new file mode 100644
index 000000000..25c9a8c14
--- /dev/null
+++ b/src/os/stat_plan9.go
@@ -0,0 +1,110 @@
+// Copyright 2011 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 (
+	"syscall"
+	"time"
+)
+
+func sameFile(fs1, fs2 *fileStat) bool {
+	a := fs1.sys.(*syscall.Dir)
+	b := fs2.sys.(*syscall.Dir)
+	return a.Qid.Path == b.Qid.Path && a.Type == b.Type && a.Dev == b.Dev
+}
+
+func fileInfoFromStat(d *syscall.Dir) FileInfo {
+	fs := &fileStat{
+		name:    d.Name,
+		size:    int64(d.Length),
+		modTime: time.Unix(int64(d.Mtime), 0),
+		sys:     d,
+	}
+	fs.mode = FileMode(d.Mode & 0777)
+	if d.Mode&syscall.DMDIR != 0 {
+		fs.mode |= ModeDir
+	}
+	if d.Mode&syscall.DMAPPEND != 0 {
+		fs.mode |= ModeAppend
+	}
+	if d.Mode&syscall.DMEXCL != 0 {
+		fs.mode |= ModeExclusive
+	}
+	if d.Mode&syscall.DMTMP != 0 {
+		fs.mode |= ModeTemporary
+	}
+	return fs
+}
+
+// arg is an open *File or a path string.
+func dirstat(arg interface{}) (*syscall.Dir, error) {
+	var name string
+
+	// This is big enough for most stat messages
+	// and rounded to a multiple of 128 bytes.
+	size := (syscall.STATFIXLEN + 16*4 + 128) &^ 128
+
+	for i := 0; i < 2; i++ {
+		buf := make([]byte, size)
+
+		var n int
+		var err error
+		switch a := arg.(type) {
+		case *File:
+			name = a.name
+			n, err = syscall.Fstat(a.fd, buf)
+		case string:
+			name = a
+			n, err = syscall.Stat(a, buf)
+		default:
+			panic("phase error in dirstat")
+		}
+		if err != nil {
+			return nil, &PathError{"stat", name, err}
+		}
+		if n < syscall.STATFIXLEN {
+			return nil, &PathError{"stat", name, syscall.ErrShortStat}
+		}
+
+		// Pull the real size out of the stat message.
+		size = int(uint16(buf[0]) | uint16(buf[1])<<8)
+
+		// If the stat message is larger than our buffer we will
+		// go around the loop and allocate one that is big enough.
+		if size > n {
+			continue
+		}
+
+		d, err := syscall.UnmarshalDir(buf[:n])
+		if err != nil {
+			return nil, &PathError{"stat", name, err}
+		}
+		return d, nil
+	}
+	return nil, &PathError{"stat", name, syscall.ErrBadStat}
+}
+
+// Stat returns a FileInfo describing the named file.
+// If there is an error, it will be of type *PathError.
+func Stat(name string) (fi FileInfo, err error) {
+	d, err := dirstat(name)
+	if err != nil {
+		return nil, err
+	}
+	return fileInfoFromStat(d), nil
+}
+
+// Lstat returns a FileInfo describing the named file.
+// If the file is a symbolic link, the returned FileInfo
+// describes the symbolic link.  Lstat makes no attempt to follow the link.
+// If there is an error, it will be of type *PathError.
+func Lstat(name string) (fi FileInfo, err error) {
+	return Stat(name)
+}
+
+// For testing.
+func atime(fi FileInfo) time.Time {
+	return time.Unix(int64(fi.Sys().(*syscall.Dir).Atime), 0)
+}
diff --git a/src/os/stat_solaris.go b/src/os/stat_solaris.go
new file mode 100644
index 000000000..605c1d9b6
--- /dev/null
+++ b/src/os/stat_solaris.go
@@ -0,0 +1,61 @@
+// 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 (
+	"syscall"
+	"time"
+)
+
+func sameFile(fs1, fs2 *fileStat) bool {
+	stat1 := fs1.sys.(*syscall.Stat_t)
+	stat2 := fs2.sys.(*syscall.Stat_t)
+	return stat1.Dev == stat2.Dev && stat1.Ino == stat2.Ino
+}
+
+func fileInfoFromStat(st *syscall.Stat_t, name string) FileInfo {
+	fs := &fileStat{
+		name:    basename(name),
+		size:    int64(st.Size),
+		modTime: timespecToTime(st.Mtim),
+		sys:     st,
+	}
+	fs.mode = FileMode(st.Mode & 0777)
+	switch st.Mode & syscall.S_IFMT {
+	case syscall.S_IFBLK:
+		fs.mode |= ModeDevice
+	case syscall.S_IFCHR:
+		fs.mode |= ModeDevice | ModeCharDevice
+	case syscall.S_IFDIR:
+		fs.mode |= ModeDir
+	case syscall.S_IFIFO:
+		fs.mode |= ModeNamedPipe
+	case syscall.S_IFLNK:
+		fs.mode |= ModeSymlink
+	case syscall.S_IFREG:
+		// nothing to do
+	case syscall.S_IFSOCK:
+		fs.mode |= ModeSocket
+	}
+	if st.Mode&syscall.S_ISGID != 0 {
+		fs.mode |= ModeSetgid
+	}
+	if st.Mode&syscall.S_ISUID != 0 {
+		fs.mode |= ModeSetuid
+	}
+	if st.Mode&syscall.S_ISVTX != 0 {
+		fs.mode |= ModeSticky
+	}
+	return fs
+}
+
+func timespecToTime(ts syscall.Timespec) time.Time {
+	return time.Unix(int64(ts.Sec), int64(ts.Nsec))
+}
+
+// For testing.
+func atime(fi FileInfo) time.Time {
+	return timespecToTime(fi.Sys().(*syscall.Stat_t).Atim)
+}
diff --git a/src/os/stat_windows.go b/src/os/stat_windows.go
new file mode 100644
index 000000000..f396c1db3
--- /dev/null
+++ b/src/os/stat_windows.go
@@ -0,0 +1,170 @@
+// 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 (
+	"syscall"
+	"unsafe"
+)
+
+// Stat returns the FileInfo structure describing file.
+// If there is an error, it will be of type *PathError.
+func (file *File) Stat() (fi FileInfo, err error) {
+	if file == nil {
+		return nil, ErrInvalid
+	}
+	if file == nil || file.fd < 0 {
+		return nil, syscall.EINVAL
+	}
+	if file.isdir() {
+		// I don't know any better way to do that for directory
+		return Stat(file.name)
+	}
+	if file.name == DevNull {
+		return &devNullStat, nil
+	}
+	var d syscall.ByHandleFileInformation
+	e := syscall.GetFileInformationByHandle(syscall.Handle(file.fd), &d)
+	if e != nil {
+		return nil, &PathError{"GetFileInformationByHandle", file.name, e}
+	}
+	return &fileStat{
+		name: basename(file.name),
+		sys: syscall.Win32FileAttributeData{
+			FileAttributes: d.FileAttributes,
+			CreationTime:   d.CreationTime,
+			LastAccessTime: d.LastAccessTime,
+			LastWriteTime:  d.LastWriteTime,
+			FileSizeHigh:   d.FileSizeHigh,
+			FileSizeLow:    d.FileSizeLow,
+		},
+		vol:   d.VolumeSerialNumber,
+		idxhi: d.FileIndexHigh,
+		idxlo: d.FileIndexLow,
+	}, nil
+}
+
+// Stat returns a FileInfo structure describing the named file.
+// If there is an error, it will be of type *PathError.
+func Stat(name string) (fi FileInfo, err error) {
+	for {
+		fi, err = Lstat(name)
+		if err != nil {
+			return
+		}
+		if fi.Mode()&ModeSymlink == 0 {
+			return
+		}
+		name, err = Readlink(name)
+		if err != nil {
+			return
+		}
+	}
+	return fi, err
+}
+
+// Lstat returns the FileInfo structure describing the named file.
+// If the file is a symbolic link, the returned FileInfo
+// describes the symbolic link.  Lstat makes no attempt to follow the link.
+// If there is an error, it will be of type *PathError.
+func Lstat(name string) (fi FileInfo, err error) {
+	if len(name) == 0 {
+		return nil, &PathError{"Lstat", name, syscall.Errno(syscall.ERROR_PATH_NOT_FOUND)}
+	}
+	if name == DevNull {
+		return &devNullStat, nil
+	}
+	fs := &fileStat{name: basename(name)}
+	namep, e := syscall.UTF16PtrFromString(name)
+	if e != nil {
+		return nil, &PathError{"Lstat", name, e}
+	}
+	e = syscall.GetFileAttributesEx(namep, syscall.GetFileExInfoStandard, (*byte)(unsafe.Pointer(&fs.sys)))
+	if e != nil {
+		return nil, &PathError{"GetFileAttributesEx", name, e}
+	}
+	fs.path = name
+	if !isAbs(fs.path) {
+		fs.path, e = syscall.FullPath(fs.path)
+		if e != nil {
+			return nil, e
+		}
+	}
+	return fs, nil
+}
+
+// basename removes trailing slashes and the leading
+// directory name and drive letter from path name.
+func basename(name string) string {
+	// Remove drive letter
+	if len(name) == 2 && name[1] == ':' {
+		name = "."
+	} else if len(name) > 2 && name[1] == ':' {
+		name = name[2:]
+	}
+	i := len(name) - 1
+	// Remove trailing slashes
+	for ; i > 0 && (name[i] == '/' || name[i] == '\\'); i-- {
+		name = name[:i]
+	}
+	// Remove leading directory name
+	for i--; i >= 0; i-- {
+		if name[i] == '/' || name[i] == '\\' {
+			name = name[i+1:]
+			break
+		}
+	}
+	return name
+}
+
+func isAbs(path string) (b bool) {
+	v := volumeName(path)
+	if v == "" {
+		return false
+	}
+	path = path[len(v):]
+	if path == "" {
+		return false
+	}
+	return IsPathSeparator(path[0])
+}
+
+func volumeName(path string) (v string) {
+	if len(path) < 2 {
+		return ""
+	}
+	// with drive letter
+	c := path[0]
+	if path[1] == ':' &&
+		('0' <= c && c <= '9' || 'a' <= c && c <= 'z' ||
+			'A' <= c && c <= 'Z') {
+		return path[:2]
+	}
+	// is it UNC
+	if l := len(path); l >= 5 && IsPathSeparator(path[0]) && IsPathSeparator(path[1]) &&
+		!IsPathSeparator(path[2]) && path[2] != '.' {
+		// first, leading `\\` and next shouldn't be `\`. its server name.
+		for n := 3; n < l-1; n++ {
+			// second, next '\' shouldn't be repeated.
+			if IsPathSeparator(path[n]) {
+				n++
+				// third, following something characters. its share name.
+				if !IsPathSeparator(path[n]) {
+					if path[n] == '.' {
+						break
+					}
+					for ; n < l; n++ {
+						if IsPathSeparator(path[n]) {
+							break
+						}
+					}
+					return path[:n]
+				}
+				break
+			}
+		}
+	}
+	return ""
+}
diff --git a/src/os/str.go b/src/os/str.go
new file mode 100644
index 000000000..e3606b61e
--- /dev/null
+++ b/src/os/str.go
@@ -0,0 +1,22 @@
+// 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.
+
+// +build plan9
+
+package os
+
+func itoa(val int) string { // do it here rather than with fmt to avoid dependency
+	if val < 0 {
+		return "-" + itoa(-val)
+	}
+	var buf [32]byte // big enough for int64
+	i := len(buf) - 1
+	for val >= 10 {
+		buf[i] = byte(val%10 + '0')
+		i--
+		val /= 10
+	}
+	buf[i] = byte(val + '0')
+	return string(buf[i:])
+}
diff --git a/src/os/sys_bsd.go b/src/os/sys_bsd.go
new file mode 100644
index 000000000..8ad5e2183
--- /dev/null
+++ b/src/os/sys_bsd.go
@@ -0,0 +1,20 @@
+// 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.
+
+// +build darwin dragonfly freebsd nacl netbsd openbsd
+
+// os code shared between *BSD systems including OS X (Darwin)
+// and FreeBSD.
+
+package os
+
+import "syscall"
+
+func hostname() (name string, err error) {
+	name, err = syscall.Sysctl("kern.hostname")
+	if err != nil {
+		return "", NewSyscallError("sysctl kern.hostname", err)
+	}
+	return name, nil
+}
diff --git a/src/os/sys_darwin.go b/src/os/sys_darwin.go
new file mode 100644
index 000000000..7a8330abb
--- /dev/null
+++ b/src/os/sys_darwin.go
@@ -0,0 +1,31 @@
+// Copyright 2014 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 "syscall"
+
+// supportsCloseOnExec reports whether the platform supports the
+// O_CLOEXEC flag.
+var supportsCloseOnExec bool
+
+func init() {
+	// Seems like kern.osreldate is veiled on latest OS X. We use
+	// kern.osrelease instead.
+	osver, err := syscall.Sysctl("kern.osrelease")
+	if err != nil {
+		return
+	}
+	var i int
+	for i = range osver {
+		if osver[i] != '.' {
+			continue
+		}
+	}
+	// The O_CLOEXEC flag was introduced in OS X 10.7 (Darwin
+	// 11.0.0). See http://support.apple.com/kb/HT1633.
+	if i > 2 || i == 2 && osver[0] >= '1' && osver[1] >= '1' {
+		supportsCloseOnExec = true
+	}
+}
diff --git a/src/os/sys_freebsd.go b/src/os/sys_freebsd.go
new file mode 100644
index 000000000..273c2df1c
--- /dev/null
+++ b/src/os/sys_freebsd.go
@@ -0,0 +1,23 @@
+// Copyright 2014 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 "syscall"
+
+// supportsCloseOnExec reports whether the platform supports the
+// O_CLOEXEC flag.
+var supportsCloseOnExec bool
+
+func init() {
+	osrel, err := syscall.SysctlUint32("kern.osreldate")
+	if err != nil {
+		return
+	}
+	// The O_CLOEXEC flag was introduced in FreeBSD 8.3.
+	// See http://www.freebsd.org/doc/en/books/porters-handbook/freebsd-versions.html.
+	if osrel >= 803000 {
+		supportsCloseOnExec = true
+	}
+}
diff --git a/src/os/sys_linux.go b/src/os/sys_linux.go
new file mode 100644
index 000000000..76cdf5043
--- /dev/null
+++ b/src/os/sys_linux.go
@@ -0,0 +1,26 @@
+// 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.
+
+// Linux-specific
+
+package os
+
+func hostname() (name string, err error) {
+	f, err := Open("/proc/sys/kernel/hostname")
+	if err != nil {
+		return "", err
+	}
+	defer f.Close()
+
+	var buf [512]byte // Enough for a DNS name.
+	n, err := f.Read(buf[0:])
+	if err != nil {
+		return "", err
+	}
+
+	if n > 0 && buf[n-1] == '\n' {
+		n--
+	}
+	return string(buf[0:n]), nil
+}
diff --git a/src/os/sys_nacl.go b/src/os/sys_nacl.go
new file mode 100644
index 000000000..07907c847
--- /dev/null
+++ b/src/os/sys_nacl.go
@@ -0,0 +1,9 @@
+// Copyright 2014 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
+
+// supportsCloseOnExec reports whether the platform supports the
+// O_CLOEXEC flag.
+const supportsCloseOnExec = false
diff --git a/src/os/sys_plan9.go b/src/os/sys_plan9.go
new file mode 100644
index 000000000..07a7905f4
--- /dev/null
+++ b/src/os/sys_plan9.go
@@ -0,0 +1,26 @@
+// Copyright 2011 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.
+
+// Plan 9-specific
+
+package os
+
+func hostname() (name string, err error) {
+	f, err := Open("#c/sysname")
+	if err != nil {
+		return "", err
+	}
+	defer f.Close()
+
+	var buf [128]byte
+	n, err := f.Read(buf[:len(buf)-1])
+
+	if err != nil {
+		return "", err
+	}
+	if n > 0 {
+		buf[n] = 0
+	}
+	return string(buf[0:n]), nil
+}
diff --git a/src/os/sys_solaris.go b/src/os/sys_solaris.go
new file mode 100644
index 000000000..917e8f2b0
--- /dev/null
+++ b/src/os/sys_solaris.go
@@ -0,0 +1,11 @@
+// Copyright 2013 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 "syscall"
+
+func hostname() (name string, err error) {
+	return syscall.Gethostname()
+}
diff --git a/src/os/sys_unix.go b/src/os/sys_unix.go
new file mode 100644
index 000000000..39c20dc73
--- /dev/null
+++ b/src/os/sys_unix.go
@@ -0,0 +1,11 @@
+// Copyright 2014 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.
+
+// +build dragonfly linux netbsd openbsd solaris
+
+package os
+
+// supportsCloseOnExec reports whether the platform supports the
+// O_CLOEXEC flag.
+const supportsCloseOnExec = true
diff --git a/src/os/sys_windows.go b/src/os/sys_windows.go
new file mode 100644
index 000000000..92617de5e
--- /dev/null
+++ b/src/os/sys_windows.go
@@ -0,0 +1,15 @@
+// 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 "syscall"
+
+func hostname() (name string, err error) {
+	s, e := syscall.ComputerName()
+	if e != nil {
+		return "", NewSyscallError("ComputerName", e)
+	}
+	return s, nil
+}
diff --git a/src/os/types.go b/src/os/types.go
new file mode 100644
index 000000000..473d431d4
--- /dev/null
+++ b/src/os/types.go
@@ -0,0 +1,118 @@
+// 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 (
+	"syscall"
+	"time"
+)
+
+// Getpagesize returns the underlying system's memory page size.
+func Getpagesize() int { return syscall.Getpagesize() }
+
+// A FileInfo describes a file and is returned by Stat and Lstat.
+type FileInfo interface {
+	Name() string       // base name of the file
+	Size() int64        // length in bytes for regular files; system-dependent for others
+	Mode() FileMode     // file mode bits
+	ModTime() time.Time // modification time
+	IsDir() bool        // abbreviation for Mode().IsDir()
+	Sys() interface{}   // underlying data source (can return nil)
+}
+
+// A FileMode represents a file's mode and permission bits.
+// The bits have the same definition on all systems, so that
+// information about files can be moved from one system
+// to another portably.  Not all bits apply to all systems.
+// The only required bit is ModeDir for directories.
+type FileMode uint32
+
+// The defined file mode bits are the most significant bits of the FileMode.
+// The nine least-significant bits are the standard Unix rwxrwxrwx permissions.
+// The values of these bits should be considered part of the public API and
+// may be used in wire protocols or disk representations: they must not be
+// changed, although new bits might be added.
+const (
+	// The single letters are the abbreviations
+	// used by the String method's formatting.
+	ModeDir        FileMode = 1 << (32 - 1 - iota) // d: is a directory
+	ModeAppend                                     // a: append-only
+	ModeExclusive                                  // l: exclusive use
+	ModeTemporary                                  // T: temporary file (not backed up)
+	ModeSymlink                                    // L: symbolic link
+	ModeDevice                                     // D: device file
+	ModeNamedPipe                                  // p: named pipe (FIFO)
+	ModeSocket                                     // S: Unix domain socket
+	ModeSetuid                                     // u: setuid
+	ModeSetgid                                     // g: setgid
+	ModeCharDevice                                 // c: Unix character device, when ModeDevice is set
+	ModeSticky                                     // t: sticky
+
+	// Mask for the type bits. For regular files, none will be set.
+	ModeType = ModeDir | ModeSymlink | ModeNamedPipe | ModeSocket | ModeDevice
+
+	ModePerm FileMode = 0777 // permission bits
+)
+
+func (m FileMode) String() string {
+	const str = "dalTLDpSugct"
+	var buf [32]byte // Mode is uint32.
+	w := 0
+	for i, c := range str {
+		if m&(1<<uint(32-1-i)) != 0 {
+			buf[w] = byte(c)
+			w++
+		}
+	}
+	if w == 0 {
+		buf[w] = '-'
+		w++
+	}
+	const rwx = "rwxrwxrwx"
+	for i, c := range rwx {
+		if m&(1<<uint(9-1-i)) != 0 {
+			buf[w] = byte(c)
+		} else {
+			buf[w] = '-'
+		}
+		w++
+	}
+	return string(buf[:w])
+}
+
+// IsDir reports whether m describes a directory.
+// That is, it tests for the ModeDir bit being set in m.
+func (m FileMode) IsDir() bool {
+	return m&ModeDir != 0
+}
+
+// IsRegular reports whether m describes a regular file.
+// That is, it tests that no mode type bits are set.
+func (m FileMode) IsRegular() bool {
+	return m&ModeType == 0
+}
+
+// Perm returns the Unix permission bits in m.
+func (m FileMode) Perm() FileMode {
+	return m & ModePerm
+}
+
+func (fs *fileStat) Name() string { return fs.name }
+func (fs *fileStat) IsDir() bool  { return fs.Mode().IsDir() }
+
+// SameFile reports whether fi1 and fi2 describe the same file.
+// For example, on Unix this means that the device and inode fields
+// of the two underlying structures are identical; on other systems
+// the decision may be based on the path names.
+// SameFile only applies to results returned by this package's Stat.
+// It returns false in other cases.
+func SameFile(fi1, fi2 FileInfo) bool {
+	fs1, ok1 := fi1.(*fileStat)
+	fs2, ok2 := fi2.(*fileStat)
+	if !ok1 || !ok2 {
+		return false
+	}
+	return sameFile(fs1, fs2)
+}
diff --git a/src/os/types_notwin.go b/src/os/types_notwin.go
new file mode 100644
index 000000000..ea1a07393
--- /dev/null
+++ b/src/os/types_notwin.go
@@ -0,0 +1,25 @@
+// 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.
+
+// +build !windows
+
+package os
+
+import (
+	"time"
+)
+
+// A fileStat is the implementation of FileInfo returned by Stat and Lstat.
+type fileStat struct {
+	name    string
+	size    int64
+	mode    FileMode
+	modTime time.Time
+	sys     interface{}
+}
+
+func (fs *fileStat) Size() int64        { return fs.size }
+func (fs *fileStat) Mode() FileMode     { return fs.mode }
+func (fs *fileStat) ModTime() time.Time { return fs.modTime }
+func (fs *fileStat) Sys() interface{}   { return fs.sys }
diff --git a/src/os/types_windows.go b/src/os/types_windows.go
new file mode 100644
index 000000000..7b2e54698
--- /dev/null
+++ b/src/os/types_windows.go
@@ -0,0 +1,107 @@
+// 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 (
+	"sync"
+	"syscall"
+	"time"
+)
+
+// A fileStat is the implementation of FileInfo returned by Stat and Lstat.
+type fileStat struct {
+	name string
+	sys  syscall.Win32FileAttributeData
+
+	// used to implement SameFile
+	sync.Mutex
+	path  string
+	vol   uint32
+	idxhi uint32
+	idxlo uint32
+}
+
+func (fs *fileStat) Size() int64 {
+	return int64(fs.sys.FileSizeHigh)<<32 + int64(fs.sys.FileSizeLow)
+}
+
+func (fs *fileStat) Mode() (m FileMode) {
+	if fs == &devNullStat {
+		return ModeDevice | ModeCharDevice | 0666
+	}
+	if fs.sys.FileAttributes&syscall.FILE_ATTRIBUTE_DIRECTORY != 0 {
+		m |= ModeDir | 0111
+	}
+	if fs.sys.FileAttributes&syscall.FILE_ATTRIBUTE_READONLY != 0 {
+		m |= 0444
+	} else {
+		m |= 0666
+	}
+	if fs.sys.FileAttributes&syscall.FILE_ATTRIBUTE_REPARSE_POINT != 0 {
+		m |= ModeSymlink
+	}
+	return m
+}
+
+func (fs *fileStat) ModTime() time.Time {
+	return time.Unix(0, fs.sys.LastWriteTime.Nanoseconds())
+}
+
+// Sys returns syscall.Win32FileAttributeData for file fs.
+func (fs *fileStat) Sys() interface{} { return &fs.sys }
+
+func (fs *fileStat) loadFileId() error {
+	fs.Lock()
+	defer fs.Unlock()
+	if fs.path == "" {
+		// already done
+		return nil
+	}
+	pathp, err := syscall.UTF16PtrFromString(fs.path)
+	if err != nil {
+		return err
+	}
+	h, err := syscall.CreateFile(pathp, 0, 0, nil, syscall.OPEN_EXISTING, syscall.FILE_FLAG_BACKUP_SEMANTICS, 0)
+	if err != nil {
+		return err
+	}
+	defer syscall.CloseHandle(h)
+	var i syscall.ByHandleFileInformation
+	err = syscall.GetFileInformationByHandle(syscall.Handle(h), &i)
+	if err != nil {
+		return err
+	}
+	fs.path = ""
+	fs.vol = i.VolumeSerialNumber
+	fs.idxhi = i.FileIndexHigh
+	fs.idxlo = i.FileIndexLow
+	return nil
+}
+
+// devNullStat is fileStat structure describing DevNull file ("NUL").
+var devNullStat = fileStat{
+	name: DevNull,
+	// hopefully this will work for SameFile
+	vol:   0,
+	idxhi: 0,
+	idxlo: 0,
+}
+
+func sameFile(fs1, fs2 *fileStat) bool {
+	e := fs1.loadFileId()
+	if e != nil {
+		return false
+	}
+	e = fs2.loadFileId()
+	if e != nil {
+		return false
+	}
+	return fs1.vol == fs2.vol && fs1.idxhi == fs2.idxhi && fs1.idxlo == fs2.idxlo
+}
+
+// For testing.
+func atime(fi FileInfo) time.Time {
+	return time.Unix(0, fi.Sys().(*syscall.Win32FileAttributeData).LastAccessTime.Nanoseconds())
+}
diff --git a/src/os/user/lookup.go b/src/os/user/lookup.go
new file mode 100644
index 000000000..09f00c7bd
--- /dev/null
+++ b/src/os/user/lookup.go
@@ -0,0 +1,22 @@
+// Copyright 2011 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 user
+
+// Current returns the current user.
+func Current() (*User, error) {
+	return current()
+}
+
+// Lookup looks up a user by username. If the user cannot be found, the
+// returned error is of type UnknownUserError.
+func Lookup(username string) (*User, error) {
+	return lookup(username)
+}
+
+// LookupId looks up a user by userid. If the user cannot be found, the
+// returned error is of type UnknownUserIdError.
+func LookupId(uid string) (*User, error) {
+	return lookupId(uid)
+}
diff --git a/src/os/user/lookup_plan9.go b/src/os/user/lookup_plan9.go
new file mode 100644
index 000000000..f7ef3482b
--- /dev/null
+++ b/src/os/user/lookup_plan9.go
@@ -0,0 +1,46 @@
+// Copyright 2013 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 user
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"syscall"
+)
+
+// Partial os/user support on Plan 9.
+// Supports Current(), but not Lookup()/LookupId().
+// The latter two would require parsing /adm/users.
+const (
+	userFile = "/dev/user"
+)
+
+func current() (*User, error) {
+	ubytes, err := ioutil.ReadFile(userFile)
+	if err != nil {
+		return nil, fmt.Errorf("user: %s", err)
+	}
+
+	uname := string(ubytes)
+
+	u := &User{
+		Uid:      uname,
+		Gid:      uname,
+		Username: uname,
+		Name:     uname,
+		HomeDir:  os.Getenv("home"),
+	}
+
+	return u, nil
+}
+
+func lookup(username string) (*User, error) {
+	return nil, syscall.EPLAN9
+}
+
+func lookupId(uid string) (*User, error) {
+	return nil, syscall.EPLAN9
+}
diff --git a/src/os/user/lookup_stubs.go b/src/os/user/lookup_stubs.go
new file mode 100644
index 000000000..4fb0e3c6e
--- /dev/null
+++ b/src/os/user/lookup_stubs.go
@@ -0,0 +1,28 @@
+// Copyright 2011 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.
+
+// +build !cgo,!windows,!plan9 android
+
+package user
+
+import (
+	"fmt"
+	"runtime"
+)
+
+func init() {
+	implemented = false
+}
+
+func current() (*User, error) {
+	return nil, fmt.Errorf("user: Current not implemented on %s/%s", runtime.GOOS, runtime.GOARCH)
+}
+
+func lookup(username string) (*User, error) {
+	return nil, fmt.Errorf("user: Lookup not implemented on %s/%s", runtime.GOOS, runtime.GOARCH)
+}
+
+func lookupId(uid string) (*User, error) {
+	return nil, fmt.Errorf("user: LookupId not implemented on %s/%s", runtime.GOOS, runtime.GOARCH)
+}
diff --git a/src/os/user/lookup_unix.go b/src/os/user/lookup_unix.go
new file mode 100644
index 000000000..0871473df
--- /dev/null
+++ b/src/os/user/lookup_unix.go
@@ -0,0 +1,112 @@
+// Copyright 2011 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.
+
+// +build darwin dragonfly freebsd !android,linux netbsd openbsd solaris
+// +build cgo
+
+package user
+
+import (
+	"fmt"
+	"runtime"
+	"strconv"
+	"strings"
+	"syscall"
+	"unsafe"
+)
+
+/*
+#include <unistd.h>
+#include <sys/types.h>
+#include <pwd.h>
+#include <stdlib.h>
+
+static int mygetpwuid_r(int uid, struct passwd *pwd,
+	char *buf, size_t buflen, struct passwd **result) {
+ return getpwuid_r(uid, pwd, buf, buflen, result);
+}
+*/
+import "C"
+
+func current() (*User, error) {
+	return lookupUnix(syscall.Getuid(), "", false)
+}
+
+func lookup(username string) (*User, error) {
+	return lookupUnix(-1, username, true)
+}
+
+func lookupId(uid string) (*User, error) {
+	i, e := strconv.Atoi(uid)
+	if e != nil {
+		return nil, e
+	}
+	return lookupUnix(i, "", false)
+}
+
+func lookupUnix(uid int, username string, lookupByName bool) (*User, error) {
+	var pwd C.struct_passwd
+	var result *C.struct_passwd
+
+	var bufSize C.long
+	if runtime.GOOS == "dragonfly" || runtime.GOOS == "freebsd" {
+		// DragonFly and FreeBSD do not have _SC_GETPW_R_SIZE_MAX
+		// and just return -1.  So just use the same
+		// size that Linux returns.
+		bufSize = 1024
+	} else {
+		bufSize = C.sysconf(C._SC_GETPW_R_SIZE_MAX)
+		if bufSize <= 0 || bufSize > 1<<20 {
+			return nil, fmt.Errorf("user: unreasonable _SC_GETPW_R_SIZE_MAX of %d", bufSize)
+		}
+	}
+	buf := C.malloc(C.size_t(bufSize))
+	defer C.free(buf)
+	var rv C.int
+	if lookupByName {
+		nameC := C.CString(username)
+		defer C.free(unsafe.Pointer(nameC))
+		rv = C.getpwnam_r(nameC,
+			&pwd,
+			(*C.char)(buf),
+			C.size_t(bufSize),
+			&result)
+		if rv != 0 {
+			return nil, fmt.Errorf("user: lookup username %s: %s", username, syscall.Errno(rv))
+		}
+		if result == nil {
+			return nil, UnknownUserError(username)
+		}
+	} else {
+		// mygetpwuid_r is a wrapper around getpwuid_r to
+		// to avoid using uid_t because C.uid_t(uid) for
+		// unknown reasons doesn't work on linux.
+		rv = C.mygetpwuid_r(C.int(uid),
+			&pwd,
+			(*C.char)(buf),
+			C.size_t(bufSize),
+			&result)
+		if rv != 0 {
+			return nil, fmt.Errorf("user: lookup userid %d: %s", uid, syscall.Errno(rv))
+		}
+		if result == nil {
+			return nil, UnknownUserIdError(uid)
+		}
+	}
+	u := &User{
+		Uid:      strconv.Itoa(int(pwd.pw_uid)),
+		Gid:      strconv.Itoa(int(pwd.pw_gid)),
+		Username: C.GoString(pwd.pw_name),
+		Name:     C.GoString(pwd.pw_gecos),
+		HomeDir:  C.GoString(pwd.pw_dir),
+	}
+	// The pw_gecos field isn't quite standardized.  Some docs
+	// say: "It is expected to be a comma separated list of
+	// personal data where the first item is the full name of the
+	// user."
+	if i := strings.Index(u.Name, ","); i >= 0 {
+		u.Name = u.Name[:i]
+	}
+	return u, nil
+}
diff --git a/src/os/user/lookup_windows.go b/src/os/user/lookup_windows.go
new file mode 100644
index 000000000..99c325ff0
--- /dev/null
+++ b/src/os/user/lookup_windows.go
@@ -0,0 +1,149 @@
+// Copyright 2012 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 user
+
+import (
+	"fmt"
+	"syscall"
+	"unsafe"
+)
+
+func isDomainJoined() (bool, error) {
+	var domain *uint16
+	var status uint32
+	err := syscall.NetGetJoinInformation(nil, &domain, &status)
+	if err != nil {
+		return false, err
+	}
+	syscall.NetApiBufferFree((*byte)(unsafe.Pointer(domain)))
+	return status == syscall.NetSetupDomainName, nil
+}
+
+func lookupFullNameDomain(domainAndUser string) (string, error) {
+	return syscall.TranslateAccountName(domainAndUser,
+		syscall.NameSamCompatible, syscall.NameDisplay, 50)
+}
+
+func lookupFullNameServer(servername, username string) (string, error) {
+	s, e := syscall.UTF16PtrFromString(servername)
+	if e != nil {
+		return "", e
+	}
+	u, e := syscall.UTF16PtrFromString(username)
+	if e != nil {
+		return "", e
+	}
+	var p *byte
+	e = syscall.NetUserGetInfo(s, u, 10, &p)
+	if e != nil {
+		return "", e
+	}
+	defer syscall.NetApiBufferFree(p)
+	i := (*syscall.UserInfo10)(unsafe.Pointer(p))
+	if i.FullName == nil {
+		return "", nil
+	}
+	name := syscall.UTF16ToString((*[1024]uint16)(unsafe.Pointer(i.FullName))[:])
+	return name, nil
+}
+
+func lookupFullName(domain, username, domainAndUser string) (string, error) {
+	joined, err := isDomainJoined()
+	if err == nil && joined {
+		name, err := lookupFullNameDomain(domainAndUser)
+		if err == nil {
+			return name, nil
+		}
+	}
+	name, err := lookupFullNameServer(domain, username)
+	if err == nil {
+		return name, nil
+	}
+	// domain worked neigher as a domain nor as a server
+	// could be domain server unavailable
+	// pretend username is fullname
+	return username, nil
+}
+
+func newUser(usid *syscall.SID, gid, dir string) (*User, error) {
+	username, domain, t, e := usid.LookupAccount("")
+	if e != nil {
+		return nil, e
+	}
+	if t != syscall.SidTypeUser {
+		return nil, fmt.Errorf("user: should be user account type, not %d", t)
+	}
+	domainAndUser := domain + `\` + username
+	uid, e := usid.String()
+	if e != nil {
+		return nil, e
+	}
+	name, e := lookupFullName(domain, username, domainAndUser)
+	if e != nil {
+		return nil, e
+	}
+	u := &User{
+		Uid:      uid,
+		Gid:      gid,
+		Username: domainAndUser,
+		Name:     name,
+		HomeDir:  dir,
+	}
+	return u, nil
+}
+
+func current() (*User, error) {
+	t, e := syscall.OpenCurrentProcessToken()
+	if e != nil {
+		return nil, e
+	}
+	defer t.Close()
+	u, e := t.GetTokenUser()
+	if e != nil {
+		return nil, e
+	}
+	pg, e := t.GetTokenPrimaryGroup()
+	if e != nil {
+		return nil, e
+	}
+	gid, e := pg.PrimaryGroup.String()
+	if e != nil {
+		return nil, e
+	}
+	dir, e := t.GetUserProfileDirectory()
+	if e != nil {
+		return nil, e
+	}
+	return newUser(u.User.Sid, gid, dir)
+}
+
+// BUG(brainman): Lookup and LookupId functions do not set
+// Gid and HomeDir fields in the User struct returned on windows.
+
+func newUserFromSid(usid *syscall.SID) (*User, error) {
+	// TODO(brainman): do not know where to get gid and dir fields
+	gid := "unknown"
+	dir := "Unknown directory"
+	return newUser(usid, gid, dir)
+}
+
+func lookup(username string) (*User, error) {
+	sid, _, t, e := syscall.LookupSID("", username)
+	if e != nil {
+		return nil, e
+	}
+	if t != syscall.SidTypeUser {
+		return nil, fmt.Errorf("user: should be user account type, not %d", t)
+	}
+	return newUserFromSid(sid)
+}
+
+func lookupId(uid string) (*User, error) {
+	sid, e := syscall.StringToSid(uid)
+	if e != nil {
+		return nil, e
+	}
+	return newUserFromSid(sid)
+}
diff --git a/src/os/user/user.go b/src/os/user/user.go
new file mode 100644
index 000000000..e8680fe54
--- /dev/null
+++ b/src/os/user/user.go
@@ -0,0 +1,43 @@
+// Copyright 2011 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 user allows user account lookups by name or id.
+package user
+
+import (
+	"strconv"
+)
+
+var implemented = true // set to false by lookup_stubs.go's init
+
+// User represents a user account.
+//
+// On posix systems Uid and Gid contain a decimal number
+// representing uid and gid. On windows Uid and Gid
+// contain security identifier (SID) in a string format.
+// On Plan 9, Uid, Gid, Username, and Name will be the
+// contents of /dev/user.
+type User struct {
+	Uid      string // user id
+	Gid      string // primary group id
+	Username string
+	Name     string
+	HomeDir  string
+}
+
+// UnknownUserIdError is returned by LookupId when
+// a user cannot be found.
+type UnknownUserIdError int
+
+func (e UnknownUserIdError) Error() string {
+	return "user: unknown userid " + strconv.Itoa(int(e))
+}
+
+// UnknownUserError is returned by Lookup when
+// a user cannot be found.
+type UnknownUserError string
+
+func (e UnknownUserError) Error() string {
+	return "user: unknown user " + string(e)
+}
diff --git a/src/os/user/user_test.go b/src/os/user/user_test.go
new file mode 100644
index 000000000..9d9420e80
--- /dev/null
+++ b/src/os/user/user_test.go
@@ -0,0 +1,89 @@
+// Copyright 2011 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 user
+
+import (
+	"runtime"
+	"testing"
+)
+
+func check(t *testing.T) {
+	if !implemented {
+		t.Skip("user: not implemented; skipping tests")
+	}
+}
+
+func TestCurrent(t *testing.T) {
+	check(t)
+
+	u, err := Current()
+	if err != nil {
+		t.Fatalf("Current: %v", err)
+	}
+	if u.HomeDir == "" {
+		t.Errorf("didn't get a HomeDir")
+	}
+	if u.Username == "" {
+		t.Errorf("didn't get a username")
+	}
+}
+
+func compare(t *testing.T, want, got *User) {
+	if want.Uid != got.Uid {
+		t.Errorf("got Uid=%q; want %q", got.Uid, want.Uid)
+	}
+	if want.Username != got.Username {
+		t.Errorf("got Username=%q; want %q", got.Username, want.Username)
+	}
+	if want.Name != got.Name {
+		t.Errorf("got Name=%q; want %q", got.Name, want.Name)
+	}
+	// TODO(brainman): fix it once we know how.
+	if runtime.GOOS == "windows" {
+		t.Skip("skipping Gid and HomeDir comparisons")
+	}
+	if want.Gid != got.Gid {
+		t.Errorf("got Gid=%q; want %q", got.Gid, want.Gid)
+	}
+	if want.HomeDir != got.HomeDir {
+		t.Errorf("got HomeDir=%q; want %q", got.HomeDir, want.HomeDir)
+	}
+}
+
+func TestLookup(t *testing.T) {
+	check(t)
+
+	if runtime.GOOS == "plan9" {
+		t.Skipf("Lookup not implemented on %q", runtime.GOOS)
+	}
+
+	want, err := Current()
+	if err != nil {
+		t.Fatalf("Current: %v", err)
+	}
+	got, err := Lookup(want.Username)
+	if err != nil {
+		t.Fatalf("Lookup: %v", err)
+	}
+	compare(t, want, got)
+}
+
+func TestLookupId(t *testing.T) {
+	check(t)
+
+	if runtime.GOOS == "plan9" {
+		t.Skipf("LookupId not implemented on %q", runtime.GOOS)
+	}
+
+	want, err := Current()
+	if err != nil {
+		t.Fatalf("Current: %v", err)
+	}
+	got, err := LookupId(want.Uid)
+	if err != nil {
+		t.Fatalf("LookupId: %v", err)
+	}
+	compare(t, want, got)
+}