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.

9 files changed, 2191 insertions, 0 deletions

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))
+}
+`