exec: new API, replace Run with Command

This removes exec.Run and replaces exec.Cmd with a
new implementation. The new exec.Cmd represents
both a currently-running command and also a command
being prepared. It has a good zero value.

You can Start + Wait on a Cmd, or simply Run it.
Start (and Run) deal with copying stdout, stdin,
and stderr between the Cmd's io.Readers and
io.Writers.

There are convenience methods to capture a command's
stdout and/or stderr.

R=r, n13m3y3r, rsc, gustavo, alex.brainman, dsymonds, r, adg, duzy.chan, mike.rosset, kevlar
CC=golang-dev
http://codereview.appspot.com/4552052

2 files changed, 20 insertions, 61 deletions

diff --git a/misc/dashboard/builder/exec.go b/misc/dashboard/builder/exec.go
index a7ef93308..0db509136 100644
--- a/misc/dashboard/builder/exec.go
+++ b/misc/dashboard/builder/exec.go
@@ -19,16 +19,11 @@ func run(envv []string, dir string, argv ...string) os.Error {
 		log.Println("run", argv)
 	}
 	argv = useBash(argv)
-	bin, err := lookPath(argv[0])
-	if err != nil {
-		return err
-	}
-	p, err := exec.Run(bin, argv, envv, dir,
-		exec.DevNull, exec.DevNull, exec.PassThrough)
-	if err != nil {
-		return err
-	}
-	return p.Close()
+	cmd := exec.Command(argv[0], argv[1:]...)
+	cmd.Dir = dir
+	cmd.Env = envv
+	cmd.Stderr = os.Stderr
+	return cmd.Run()
 }
 
 // runLog runs a process and returns the combined stdout/stderr, 
@@ -38,16 +33,7 @@ func runLog(envv []string, logfile, dir string, argv ...string) (output string,
 		log.Println("runLog", argv)
 	}
 	argv = useBash(argv)
-	bin, err := lookPath(argv[0])
-	if err != nil {
-		return
-	}
-	p, err := exec.Run(bin, argv, envv, dir,
-		exec.DevNull, exec.Pipe, exec.MergeWithStdout)
-	if err != nil {
-		return
-	}
-	defer p.Close()
+
 	b := new(bytes.Buffer)
 	var w io.Writer = b
 	if logfile != "" {
@@ -58,23 +44,22 @@ func runLog(envv []string, logfile, dir string, argv ...string) (output string,
 		defer f.Close()
 		w = io.MultiWriter(f, b)
 	}
-	_, err = io.Copy(w, p.Stdout)
-	if err != nil {
-		return
-	}
-	wait, err := p.Wait(0)
+
+	cmd := exec.Command(argv[0], argv[1:]...)
+	cmd.Dir = dir
+	cmd.Env = envv
+	cmd.Stdout = w
+	cmd.Stderr = w
+
+	err = cmd.Run()
+	output = b.String()
 	if err != nil {
+		if ws, ok := err.(*os.Waitmsg); ok {
+			exitStatus = ws.ExitStatus()
+		}
 		return
 	}
-	return b.String(), wait.WaitStatus.ExitStatus(), nil
-}
-
-// lookPath looks for cmd in $PATH if cmd does not begin with / or ./ or ../.
-func lookPath(cmd string) (string, os.Error) {
-	if strings.HasPrefix(cmd, "/") || strings.HasPrefix(cmd, "./") || strings.HasPrefix(cmd, "../") {
-		return cmd, nil
-	}
-	return exec.LookPath(cmd)
+	return
 }
 
 // useBash prefixes a list of args with 'bash' if the first argument
diff --git a/misc/goplay/goplay.go b/misc/goplay/goplay.go
index f3e2ff565..f1dc1bca5 100644
--- a/misc/goplay/goplay.go
+++ b/misc/goplay/goplay.go
@@ -5,7 +5,6 @@
 package main
 
 import (
-	"bytes"
 	"exec"
 	"flag"
 	"http"
@@ -140,32 +139,7 @@ func error(w http.ResponseWriter, out []byte, err os.Error) {
 
 // run executes the specified command and returns its output and an error.
 func run(cmd ...string) ([]byte, os.Error) {
-	// find the specified binary
-	bin, err := exec.LookPath(cmd[0])
-	if err != nil {
-		// report binary as well as the error
-		return nil, os.NewError(cmd[0] + ": " + err.String())
-	}
-
-	// run the binary and read its combined stdout and stderr into a buffer
-	p, err := exec.Run(bin, cmd, os.Environ(), "", exec.DevNull, exec.Pipe, exec.MergeWithStdout)
-	if err != nil {
-		return nil, err
-	}
-	var buf bytes.Buffer
-	io.Copy(&buf, p.Stdout)
-	w, err := p.Wait(0)
-	p.Close()
-	if err != nil {
-		return nil, err
-	}
-
-	// set the error return value if the program had a non-zero exit status
-	if !w.Exited() || w.ExitStatus() != 0 {
-		err = os.ErrorString("running " + cmd[0] + ": " + w.String())
-	}
-
-	return buf.Bytes(), err
+	return exec.Command(cmd[0], cmd[1:]...).CombinedOutput()
 }
 
 var frontPage, output *template.Template // HTML templates