Imported Upstream version 58upstream/58

5 files changed, 519 insertions, 293 deletions

diff --git a/src/pkg/exec/exec.go b/src/pkg/exec/exec.go
index 043f84728..935f24c21 100644
--- a/src/pkg/exec/exec.go
+++ b/src/pkg/exec/exec.go
@@ -7,198 +7,363 @@
 // adjustments.
 package exec
 
-// BUG(r): This package should be made even easier to use or merged into os.
-
 import (
+	"bytes"
+	"io"
 	"os"
 	"strconv"
 )
 
-// Arguments to Run.
-const (
-	DevNull = iota
-	PassThrough
-	Pipe
-	MergeWithStdout
-)
+// Error records the name of a binary that failed to be be executed
+// and the reason it failed.
+type Error struct {
+	Name  string
+	Error os.Error
+}
 
-// A Cmd represents a running command.
-// Stdin, Stdout, and Stderr are Files representing pipes
-// connected to the running command's standard input, output, and error,
-// or else nil, depending on the arguments to Run.
-// Process represents the underlying operating system process.
+func (e *Error) String() string {
+	return "exec: " + strconv.Quote(e.Name) + ": " + e.Error.String()
+}
+
+// Cmd represents an external command being prepared or run.
 type Cmd struct {
-	Stdin   *os.File
-	Stdout  *os.File
-	Stderr  *os.File
+	// Path is the path of the command to run.
+	//
+	// This is the only field that must be set to a non-zero
+	// value.
+	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 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 /dev/null.
+	//
+	// If Stdout and Stderr are are the same writer, at most one
+	// goroutine at a time will call Write.
+	Stdout io.Writer
+	Stderr io.Writer
+
+	// Process is the underlying process, once started.
 	Process *os.Process
+
+	err             os.Error // last error (from LookPath, stdin, stdout, stderr)
+	finished        bool     // when Wait was called
+	childFiles      []*os.File
+	closeAfterStart []io.Closer
+	closeAfterWait  []io.Closer
+	goroutine       []func() os.Error
+	errch           chan os.Error // one send per goroutine
 }
 
-// PathError records the name of a binary that was not
-// found on the current $PATH.
-type PathError struct {
-	Name string
+// Command returns the Cmd struct to execute the named program with
+// the given arguments.
+//
+// It sets Path and Args in the returned structure and zeroes the
+// other fields.
+//
+// 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 {
+	aname, err := LookPath(name)
+	if err != nil {
+		aname = name
+	}
+	return &Cmd{
+		Path: aname,
+		Args: append([]string{name}, arg...),
+		err:  err,
+	}
 }
 
-func (e *PathError) String() string {
-	return "command " + strconv.Quote(e.Name) + " not found in $PATH"
+// 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
 }
 
-// Given mode (DevNull, etc), return file for child
-// and file to record in Cmd structure.
-func modeToFiles(mode, fd int) (*os.File, *os.File, os.Error) {
-	switch mode {
-	case DevNull:
-		rw := os.O_WRONLY
-		if fd == 0 {
-			rw = os.O_RDONLY
-		}
-		f, err := os.OpenFile(os.DevNull, rw, 0)
-		return f, nil, err
-	case PassThrough:
-		switch fd {
-		case 0:
-			return os.Stdin, nil, nil
-		case 1:
-			return os.Stdout, nil, nil
-		case 2:
-			return os.Stderr, nil, nil
-		}
-	case Pipe:
-		r, w, err := os.Pipe()
-		if err != nil {
-			return nil, nil, err
-		}
-		if fd == 0 {
-			return r, w, nil
+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 os.Error) {
+	if c.Stdin == nil {
+		f, err = os.Open(os.DevNull)
+		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() os.Error {
+		_, err := io.Copy(pw, c.Stdin)
+		if err1 := pw.Close(); err == nil {
+			err = err1
 		}
-		return w, r, nil
+		return err
+	})
+	return pr, nil
+}
+
+func (c *Cmd) stdout() (f *os.File, err os.Error) {
+	return c.writerDescriptor(c.Stdout)
+}
+
+func (c *Cmd) stderr() (f *os.File, err os.Error) {
+	if c.Stderr != nil && interfaceEqual(c.Stderr, c.Stdout) {
+		return c.childFiles[1], nil
 	}
-	return nil, nil, os.EINVAL
+	return c.writerDescriptor(c.Stderr)
 }
 
-// Run starts the named binary running with
-// arguments argv and environment envv.
-// If the dir argument is not empty, the child changes
-// into the directory before executing the binary.
-// It returns a pointer to a new Cmd representing
-// the command or an error.
+func (c *Cmd) writerDescriptor(w io.Writer) (f *os.File, err os.Error) {
+	if w == nil {
+		f, err = os.OpenFile(os.DevNull, os.O_WRONLY, 0)
+		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() os.Error {
+		_, err := io.Copy(w, pr)
+		return err
+	})
+	return pw, nil
+}
+
+// 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.
 //
-// The arguments stdin, stdout, and stderr
-// specify how to handle standard input, output, and error.
-// The choices are DevNull (connect to /dev/null),
-// PassThrough (connect to the current process's standard stream),
-// Pipe (connect to an operating system pipe), and
-// MergeWithStdout (only for standard error; use the same
-// file descriptor as was used for standard output).
-// If an argument is Pipe, then the corresponding field (Stdin, Stdout, Stderr)
-// of the returned Cmd is the other end of the pipe.
-// Otherwise the field in Cmd is nil.
-func Run(name string, argv, envv []string, dir string, stdin, stdout, stderr int) (c *Cmd, err os.Error) {
-	c = new(Cmd)
-	var fd [3]*os.File
-
-	if fd[0], c.Stdin, err = modeToFiles(stdin, 0); err != nil {
-		goto Error
-	}
-	if fd[1], c.Stdout, err = modeToFiles(stdout, 1); err != nil {
-		goto Error
-	}
-	if stderr == MergeWithStdout {
-		fd[2] = fd[1]
-	} else if fd[2], c.Stderr, err = modeToFiles(stderr, 2); err != nil {
-		goto Error
-	}
-
-	// Run command.
-	c.Process, err = os.StartProcess(name, argv, &os.ProcAttr{Dir: dir, Files: fd[:], Env: envv})
+// If the command fails to run or doesn't complete successfully, the
+// error is of type *os.Waitmsg. Other error types may be
+// returned for I/O problems.
+func (c *Cmd) Run() os.Error {
+	if err := c.Start(); err != nil {
+		return err
+	}
+	return c.Wait()
+}
+
+// Start starts the specified command but does not wait for it to complete.
+func (c *Cmd) Start() os.Error {
+	if c.err != nil {
+		return c.err
+	}
+	if c.Process != nil {
+		return os.NewError("exec: already started")
+	}
+
+	type F func(*Cmd) (*os.File, os.Error)
+	for _, setupFd := range []F{(*Cmd).stdin, (*Cmd).stdout, (*Cmd).stderr} {
+		fd, err := setupFd(c)
+		if err != nil {
+			return err
+		}
+		c.childFiles = append(c.childFiles, fd)
+	}
+
+	var err os.Error
+	c.Process, err = os.StartProcess(c.Path, c.argv(), &os.ProcAttr{
+		Dir:   c.Dir,
+		Files: c.childFiles,
+		Env:   c.envv(),
+	})
 	if err != nil {
-		goto Error
+		return err
+	}
+
+	for _, fd := range c.closeAfterStart {
+		fd.Close()
 	}
-	if fd[0] != os.Stdin {
-		fd[0].Close()
+
+	c.errch = make(chan os.Error, len(c.goroutine))
+	for _, fn := range c.goroutine {
+		go func(fn func() os.Error) {
+			c.errch <- fn()
+		}(fn)
 	}
-	if fd[1] != os.Stdout {
-		fd[1].Close()
+
+	return nil
+}
+
+// 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 *os.Waitmsg. Other error types may be
+// returned for I/O problems.
+func (c *Cmd) Wait() os.Error {
+	if c.Process == nil {
+		return os.NewError("exec: not started")
 	}
-	if fd[2] != os.Stderr && fd[2] != fd[1] {
-		fd[2].Close()
+	if c.finished {
+		return os.NewError("exec: Wait was already called")
 	}
-	return c, nil
+	c.finished = true
+	msg, err := c.Process.Wait(0)
 
-Error:
-	if fd[0] != os.Stdin && fd[0] != nil {
-		fd[0].Close()
+	var copyError os.Error
+	for _ = range c.goroutine {
+		if err := <-c.errch; err != nil && copyError == nil {
+			copyError = err
+		}
 	}
-	if fd[1] != os.Stdout && fd[1] != nil {
-		fd[1].Close()
+
+	for _, fd := range c.closeAfterWait {
+		fd.Close()
 	}
-	if fd[2] != os.Stderr && fd[2] != nil && fd[2] != fd[1] {
-		fd[2].Close()
+
+	if err != nil {
+		return err
+	} else if !msg.Exited() || msg.ExitStatus() != 0 {
+		return msg
 	}
-	if c.Stdin != nil {
-		c.Stdin.Close()
+
+	return copyError
+}
+
+// Output runs the command and returns its standard output.
+func (c *Cmd) Output() ([]byte, os.Error) {
+	if c.Stdout != nil {
+		return nil, os.NewError("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, os.Error) {
 	if c.Stdout != nil {
-		c.Stdout.Close()
+		return nil, os.NewError("exec: Stdout already set")
 	}
 	if c.Stderr != nil {
-		c.Stderr.Close()
+		return nil, os.NewError("exec: Stderr already set")
 	}
-	if c.Process != nil {
-		c.Process.Release()
-	}
-	return nil, err
+	var b bytes.Buffer
+	c.Stdout = &b
+	c.Stderr = &b
+	err := c.Run()
+	return b.Bytes(), err
 }
 
-// Wait waits for the running command c,
-// returning the Waitmsg returned when the process exits.
-// The options are passed to the process's Wait method.
-// Setting options to 0 waits for c to exit;
-// other options cause Wait to return for other
-// process events; see package os for details.
-func (c *Cmd) Wait(options int) (*os.Waitmsg, os.Error) {
-	if c.Process == nil {
-		return nil, os.ErrorString("exec: invalid use of Cmd.Wait")
+// StdinPipe returns a pipe that will be connected to the command's
+// standard input when the command starts.
+func (c *Cmd) StdinPipe() (io.WriteCloser, os.Error) {
+	if c.Stdin != nil {
+		return nil, os.NewError("exec: Stdin already set")
 	}
-	w, err := c.Process.Wait(options)
-	if w != nil && (w.Exited() || w.Signaled()) {
-		c.Process.Release()
-		c.Process = nil
+	if c.Process != nil {
+		return nil, os.NewError("exec: StdinPipe after process started")
+	}
+	pr, pw, err := os.Pipe()
+	if err != nil {
+		return nil, err
 	}
-	return w, err
+	c.Stdin = pr
+	c.closeAfterStart = append(c.closeAfterStart, pr)
+	c.closeAfterWait = append(c.closeAfterStart, pw)
+	return pw, nil
 }
 
-// Close waits for the running command c to exit,
-// if it hasn't already, and then closes the non-nil file descriptors
-// c.Stdin, c.Stdout, and c.Stderr.
-func (c *Cmd) Close() os.Error {
+// StdoutPipe returns a pipe that will be connected to the command's
+// standard output when the command starts.
+func (c *Cmd) StdoutPipe() (io.Reader, os.Error) {
+	if c.Stdout != nil {
+		return nil, os.NewError("exec: Stdout already set")
+	}
 	if c.Process != nil {
-		// Loop on interrupt, but
-		// ignore other errors -- maybe
-		// caller has already waited for pid.
-		_, err := c.Wait(0)
-		for err == os.EINTR {
-			_, err = c.Wait(0)
-		}
+		return nil, os.NewError("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.closeAfterStart, pr)
+	return pr, nil
+}
 
-	// Close the FDs that are still open.
-	var err os.Error
-	if c.Stdin != nil && c.Stdin.Fd() >= 0 {
-		if err1 := c.Stdin.Close(); err1 != nil {
-			err = err1
-		}
+// StderrPipe returns a pipe that will be connected to the command's
+// standard error when the command starts.
+func (c *Cmd) StderrPipe() (io.Reader, os.Error) {
+	if c.Stderr != nil {
+		return nil, os.NewError("exec: Stderr already set")
 	}
-	if c.Stdout != nil && c.Stdout.Fd() >= 0 {
-		if err1 := c.Stdout.Close(); err1 != nil && err != nil {
-			err = err1
-		}
+	if c.Process != nil {
+		return nil, os.NewError("exec: StderrPipe after process started")
 	}
-	if c.Stderr != nil && c.Stderr != c.Stdout && c.Stderr.Fd() >= 0 {
-		if err1 := c.Stderr.Close(); err1 != nil && err != nil {
-			err = err1
-		}
+	pr, pw, err := os.Pipe()
+	if err != nil {
+		return nil, err
 	}
-	return err
+	c.Stderr = pw
+	c.closeAfterStart = append(c.closeAfterStart, pw)
+	c.closeAfterWait = append(c.closeAfterStart, pr)
+	return pr, nil
 }
diff --git a/src/pkg/exec/exec_test.go b/src/pkg/exec/exec_test.go
index eb8cd5fec..c45a7d70a 100644
--- a/src/pkg/exec/exec_test.go
+++ b/src/pkg/exec/exec_test.go
@@ -5,163 +5,211 @@
 package exec
 
 import (
+	"bufio"
+	"bytes"
+	"fmt"
 	"io"
-	"io/ioutil"
 	"testing"
 	"os"
+	"strconv"
+	"strings"
 )
 
-func run(argv []string, stdin, stdout, stderr int) (p *Cmd, err os.Error) {
-	exe, err := LookPath(argv[0])
-	if err != nil {
-		return nil, err
-	}
-	return Run(exe, argv, nil, "", stdin, stdout, stderr)
+func helperCommand(s ...string) *Cmd {
+	cs := []string{"-test.run=exec.TestHelperProcess", "--"}
+	cs = append(cs, s...)
+	cmd := Command(os.Args[0], cs...)
+	cmd.Env = append([]string{"GO_WANT_HELPER_PROCESS=1"}, os.Environ()...)
+	return cmd
 }
 
-func TestRunCat(t *testing.T) {
-	cmd, err := run([]string{"cat"}, Pipe, Pipe, DevNull)
+func TestEcho(t *testing.T) {
+	bs, err := helperCommand("echo", "foo bar", "baz").Output()
 	if err != nil {
-		t.Fatal("run:", err)
-	}
-	io.WriteString(cmd.Stdin, "hello, world\n")
-	cmd.Stdin.Close()
-	buf, err := ioutil.ReadAll(cmd.Stdout)
-	if err != nil {
-		t.Fatal("read:", err)
-	}
-	if string(buf) != "hello, world\n" {
-		t.Fatalf("read: got %q", buf)
+		t.Errorf("echo: %v", err)
 	}
-	if err = cmd.Close(); err != nil {
-		t.Fatal("close:", err)
+	if g, e := string(bs), "foo bar baz\n"; g != e {
+		t.Errorf("echo: want %q, got %q", e, g)
 	}
 }
 
-func TestRunEcho(t *testing.T) {
-	cmd, err := run([]string{"sh", "-c", "echo hello world"},
-		DevNull, Pipe, DevNull)
+func TestCatStdin(t *testing.T) {
+	// Cat, testing stdin and stdout.
+	input := "Input string\nLine 2"
+	p := helperCommand("cat")
+	p.Stdin = strings.NewReader(input)
+	bs, err := p.Output()
 	if err != nil {
-		t.Fatal("run:", err)
+		t.Errorf("cat: %v", err)
 	}
-	buf, err := ioutil.ReadAll(cmd.Stdout)
-	if err != nil {
-		t.Fatal("read:", err)
-	}
-	if string(buf) != "hello world\n" {
-		t.Fatalf("read: got %q", buf)
-	}
-	if err = cmd.Close(); err != nil {
-		t.Fatal("close:", err)
+	s := string(bs)
+	if s != input {
+		t.Errorf("cat: want %q, got %q", input, s)
 	}
 }
 
-func TestStderr(t *testing.T) {
-	cmd, err := run([]string{"sh", "-c", "echo hello world 1>&2"},
-		DevNull, DevNull, Pipe)
-	if err != nil {
-		t.Fatal("run:", err)
+func TestCatGoodAndBadFile(t *testing.T) {
+	// Testing combined output and error values.
+	bs, err := helperCommand("cat", "/bogus/file.foo", "exec_test.go").CombinedOutput()
+	if _, ok := err.(*os.Waitmsg); !ok {
+		t.Errorf("expected Waitmsg from cat combined; got %T: %v", err, err)
 	}
-	buf, err := ioutil.ReadAll(cmd.Stderr)
-	if err != nil {
-		t.Fatal("read:", err)
+	s := string(bs)
+	sp := strings.Split(s, "\n", 2)
+	if len(sp) != 2 {
+		t.Fatalf("expected two lines from cat; got %q", s)
 	}
-	if string(buf) != "hello world\n" {
-		t.Fatalf("read: got %q", buf)
+	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 err = cmd.Close(); err != nil {
-		t.Fatal("close:", err)
+	if !strings.Contains(body, "func TestHelperProcess(t *testing.T)") {
+		t.Errorf("expected test code; got %q (len %d)", body, len(body))
 	}
 }
 
-func TestMergeWithStdout(t *testing.T) {
-	cmd, err := run([]string{"sh", "-c", "echo hello world 1>&2"},
-		DevNull, Pipe, MergeWithStdout)
-	if err != nil {
-		t.Fatal("run:", err)
-	}
-	buf, err := ioutil.ReadAll(cmd.Stdout)
-	if err != nil {
-		t.Fatal("read:", err)
-	}
-	if string(buf) != "hello world\n" {
-		t.Fatalf("read: got %q", buf)
+
+func TestNoExistBinary(t *testing.T) {
+	// Can't run a non-existent binary
+	err := Command("/no-exist-binary").Run()
+	if err == nil {
+		t.Error("expected error from /no-exist-binary")
 	}
-	if err = cmd.Close(); err != nil {
-		t.Fatal("close:", err)
+}
+
+func TestExitStatus(t *testing.T) {
+	// Test that exit values are returned correctly
+	err := helperCommand("exit", "42").Run()
+	if werr, ok := err.(*os.Waitmsg); ok {
+		if s, e := werr.String(), "exit status 42"; s != e {
+			t.Errorf("from exit 42 got exit %q, want %q", s, e)
+		}
+	} else {
+		t.Fatalf("expected Waitmsg from exit 42; got %T: %v", err, err)
 	}
 }
 
-func TestAddEnvVar(t *testing.T) {
-	err := os.Setenv("NEWVAR", "hello world")
-	if err != nil {
-		t.Fatal("setenv:", err)
+func TestPipes(t *testing.T) {
+	check := func(what string, err os.Error) {
+		if err != nil {
+			t.Fatalf("%s: %v", what, err)
+		}
 	}
-	cmd, err := run([]string{"sh", "-c", "echo $NEWVAR"},
-		DevNull, Pipe, DevNull)
-	if err != nil {
-		t.Fatal("run:", err)
+	// Cat, testing stdin and stdout.
+	c := helperCommand("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)
 	}
-	buf, err := ioutil.ReadAll(cmd.Stdout)
-	if err != nil {
-		t.Fatal("read:", err)
+
+	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)
 	}
-	if string(buf) != "hello world\n" {
-		t.Fatalf("read: got %q", buf)
+
+	_, 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)
 	}
-	if err = cmd.Close(); err != nil {
-		t.Fatal("close:", err)
+
+	_, 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)
 	}
-}
 
-var tryargs = []string{
-	`2`,
-	`2 `,
-	"2 \t",
-	`2" "`,
-	`2 ab `,
-	`2 "ab" `,
-	`2 \ `,
-	`2 \\ `,
-	`2 \" `,
-	`2 \`,
-	`2\`,
-	`2"`,
-	`2\"`,
-	`2 "`,
-	`2 \"`,
-	``,
-	`2 ^ `,
-	`2 \^`,
+	stdin.Close()
+	err = c.Wait()
+	check("Wait", err)
 }
 
-func TestArgs(t *testing.T) {
-	for _, a := range tryargs {
-		argv := []string{
-			"awk",
-			`BEGIN{printf("%s|%s|%s",ARGV[1],ARGV[2],ARGV[3])}`,
-			"/dev/null",
-			a,
-			"EOF",
-		}
-		exe, err := LookPath(argv[0])
-		if err != nil {
-			t.Fatal("run:", err)
+// 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)
+
+	args := os.Args
+	for len(args) > 0 {
+		if args[0] == "--" {
+			args = args[1:]
+			break
 		}
-		cmd, err := Run(exe, argv, nil, "", DevNull, Pipe, DevNull)
-		if err != nil {
-			t.Fatal("run:", err)
+		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)
 		}
-		buf, err := ioutil.ReadAll(cmd.Stdout)
-		if err != nil {
-			t.Fatal("read:", err)
+		fmt.Println(iargs...)
+	case "cat":
+		if len(args) == 0 {
+			io.Copy(os.Stdout, os.Stdin)
+			return
 		}
-		expect := "/dev/null|" + a + "|EOF"
-		if string(buf) != expect {
-			t.Errorf("read: got %q expect %q", buf, expect)
+		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)
+			}
 		}
-		if err = cmd.Close(); err != nil {
-			t.Fatal("close:", err)
+		os.Exit(exit)
+	case "pipetest":
+		bufr := bufio.NewReader(os.Stdin)
+		for {
+			line, _, err := bufr.ReadLine()
+			if err == os.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 "exit":
+		n, _ := strconv.Atoi(args[0])
+		os.Exit(n)
+	default:
+		fmt.Fprintf(os.Stderr, "Unknown command %q\n", cmd)
+		os.Exit(2)
 	}
 }
diff --git a/src/pkg/exec/lp_test.go b/src/pkg/exec/lp_test.go
index 54081771e..77d8e848c 100644
--- a/src/pkg/exec/lp_test.go
+++ b/src/pkg/exec/lp_test.go
@@ -22,12 +22,12 @@ func TestLookPathNotFound(t *testing.T) {
 		if path != "" {
 			t.Fatalf("LookPath path == %q when err != nil", path)
 		}
-		perr, ok := err.(*PathError)
+		perr, ok := err.(*Error)
 		if !ok {
-			t.Fatal("LookPath error is not a PathError")
+			t.Fatal("LookPath error is not an exec.Error")
 		}
 		if perr.Name != name {
-			t.Fatalf("want PathError name %q, got %q", name, perr.Name)
+			t.Fatalf("want Error name %q, got %q", name, perr.Name)
 		}
 	}
 }
diff --git a/src/pkg/exec/lp_unix.go b/src/pkg/exec/lp_unix.go
index 44f84347b..3fc3be832 100644
--- a/src/pkg/exec/lp_unix.go
+++ b/src/pkg/exec/lp_unix.go
@@ -9,12 +9,18 @@ import (
 	"strings"
 )
 
-func canExec(file string) bool {
+// ErrNotFound is the error resulting if a path search failed to find an executable file.
+var ErrNotFound = os.ErrorString("executable file not found in $PATH")
+
+func findExecutable(file string) os.Error {
 	d, err := os.Stat(file)
 	if err != nil {
-		return false
+		return err
+	}
+	if d.IsRegular() && d.Permission()&0111 != 0 {
+		return nil
 	}
-	return d.IsRegular() && d.Permission()&0111 != 0
+	return os.EPERM
 }
 
 // LookPath searches for an executable binary named file
@@ -26,10 +32,11 @@ func LookPath(file string) (string, os.Error) {
 	// but that would not match all the Unix shells.
 
 	if strings.Contains(file, "/") {
-		if canExec(file) {
+		err := findExecutable(file)
+		if err == nil {
 			return file, nil
 		}
-		return "", &PathError{file}
+		return "", &Error{file, err}
 	}
 	pathenv := os.Getenv("PATH")
 	for _, dir := range strings.Split(pathenv, ":", -1) {
@@ -37,9 +44,9 @@ func LookPath(file string) (string, os.Error) {
 			// Unix shell semantics: path element "" means "."
 			dir = "."
 		}
-		if canExec(dir + "/" + file) {
+		if err := findExecutable(dir + "/" + file); err == nil {
 			return dir + "/" + file, nil
 		}
 	}
-	return "", &PathError{file}
+	return "", &Error{file, ErrNotFound}
 }
diff --git a/src/pkg/exec/lp_windows.go b/src/pkg/exec/lp_windows.go
index d357575fd..758861021 100644
--- a/src/pkg/exec/lp_windows.go
+++ b/src/pkg/exec/lp_windows.go
@@ -9,15 +9,21 @@ import (
 	"strings"
 )
 
-func chkStat(file string) bool {
+// ErrNotFound is the error resulting if a path search failed to find an executable file.
+var ErrNotFound = os.ErrorString("executable file not found in %PATH%")
+
+func chkStat(file string) os.Error {
 	d, err := os.Stat(file)
 	if err != nil {
-		return false
+		return err
+	}
+	if d.IsRegular() {
+		return nil
 	}
-	return d.IsRegular()
+	return os.EPERM
 }
 
-func canExec(file string, exts []string) (string, bool) {
+func findExecutable(file string, exts []string) (string, os.Error) {
 	if len(exts) == 0 {
 		return file, chkStat(file)
 	}
@@ -28,14 +34,14 @@ func canExec(file string, exts []string) (string, bool) {
 		}
 	}
 	for _, e := range exts {
-		if f := file + e; chkStat(f) {
-			return f, true
+		if f := file + e; chkStat(f) == nil {
+			return f, nil
 		}
 	}
-	return ``, false
+	return ``, ErrNotFound
 }
 
-func LookPath(file string) (string, os.Error) {
+func LookPath(file string) (f string, err os.Error) {
 	exts := []string{}
 	if x := os.Getenv(`PATHEXT`); x != `` {
 		exts = strings.Split(strings.ToLower(x), `;`, -1)
@@ -46,21 +52,21 @@ func LookPath(file string) (string, os.Error) {
 		}
 	}
 	if strings.Contains(file, `\`) || strings.Contains(file, `/`) {
-		if f, ok := canExec(file, exts); ok {
-			return f, nil
+		if f, err = findExecutable(file, exts); err == nil {
+			return
 		}
-		return ``, &PathError{file}
+		return ``, &Error{file, err}
 	}
 	if pathenv := os.Getenv(`PATH`); pathenv == `` {
-		if f, ok := canExec(`.\`+file, exts); ok {
-			return f, nil
+		if f, err = findExecutable(`.\`+file, exts); err == nil {
+			return
 		}
 	} else {
 		for _, dir := range strings.Split(pathenv, `;`, -1) {
-			if f, ok := canExec(dir+`\`+file, exts); ok {
-				return f, nil
+			if f, err = findExecutable(dir+`\`+file, exts); err == nil {
+				return
 			}
 		}
 	}
-	return ``, &PathError{file}
+	return ``, &Error{file, ErrNotFound}
 }