1 files changed, 719 insertions, 0 deletions
diff --git a/src/os/exec/exec_test.go b/src/os/exec/exec_test.go
new file mode 100644
index 000000000..197d3e8b4
--- /dev/null
+++ b/src/os/exec/exec_test.go
@@ -0,0 +1,719 @@
+// 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", "-b", "-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 {
+	return os.Stderr.Fd() + 1
+}
+
+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) {
+	switch runtime.GOOS {
+	case "nacl", "windows":
+		t.Skipf("skipping test on %q", runtime.GOOS)
+	}
+
+	// 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)
+	}
+}