os/exec: cleanup and remove duplicated code

Change-Id: Ia2f61427b1cc09064ac4c0563bccbd9b98767a0e
Reviewed-on: https://go-review.googlesource.com/18118
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/os/exec/lp_plan9.go

@@ -7,6 +7,7 @@ package exec
 import (
 	"errors"
 	"os"
+	"path/filepath"
 	"strings"
 )
 
@@ -44,9 +45,10 @@ func LookPath(file string) (string, error) {
 	}
 
 	path := os.Getenv("path")
-	for _, dir := range strings.Split(path, "\000") {
-		if err := findExecutable(dir + "/" + file); err == nil {
-			return dir + "/" + file, nil
+	for _, dir := range filepath.SplitList(path) {
+		path := filepath.Join(dir, file)
+		if err := findExecutable(path); err == nil {
+			return path, nil
 		}
 	}
 	return "", &Error{file, ErrNotFound}

src/os/exec/lp_unix.go

@@ -9,6 +9,7 @@ package exec
 import (
 	"errors"
 	"os"
+	"path/filepath"
 	"strings"
 )
 
@@ -42,16 +43,13 @@ func LookPath(file string) (string, error) {
 		}
 		return "", &Error{file, err}
 	}
-	pathenv := os.Getenv("PATH")
-	if pathenv == "" {
-		return "", &Error{file, ErrNotFound}
-	}
-	for _, dir := range strings.Split(pathenv, ":") {
+	path := os.Getenv("PATH")
+	for _, dir := range filepath.SplitList(path) {
 		if dir == "" {
 			// Unix shell semantics: path element "" means "."
 			dir = "."
 		}
-		path := dir + "/" + file
+		path := filepath.Join(dir, file)
 		if err := findExecutable(path); err == nil {
 			return path, nil
 		}

src/os/exec/lp_windows.go

@@ -7,6 +7,7 @@ package exec
 import (
 	"errors"
 	"os"
+	"path/filepath"
 	"strings"
 )
 
@@ -56,11 +57,9 @@ func findExecutable(file string, exts []string) (string, error) {
 // a suitable candidate.
 // The result may be an absolute path or a path relative to the current directory.
 func LookPath(file string) (string, error) {
+	var exts []string
 	x := os.Getenv(`PATHEXT`)
-	if x == "" {
-		x = `.COM;.EXE;.BAT;.CMD`
-	}
-	exts := []string{}
+	if x != "" {
 		for _, e := range strings.Split(strings.ToLower(x), `;`) {
 			if e == "" {
 				continue
@@ -70,6 +69,10 @@ func LookPath(file string) (string, error) {
 			}
 			exts = append(exts, e)
 		}
+	} else {
+		exts = []string{".com", ".exe", ".bat", ".cmd"}
+	}
+
 	if strings.ContainsAny(file, `:\/`) {
 		if f, err := findExecutable(file, exts); err == nil {
 			return f, nil
@@ -77,48 +80,14 @@ func LookPath(file string) (string, error) {
 			return "", &Error{file, err}
 		}
 	}
-	if f, err := findExecutable(`.\`+file, exts); err == nil {
+	if f, err := findExecutable(filepath.Join(".", file), exts); err == nil {
 		return f, nil
 	}
-	if pathenv := os.Getenv(`PATH`); pathenv != "" {
-		for _, dir := range splitList(pathenv) {
-			if f, err := findExecutable(dir+`\`+file, exts); err == nil {
+	path := os.Getenv("path")
+	for _, dir := range filepath.SplitList(path) {
+		if f, err := findExecutable(filepath.Join(dir, file), exts); err == nil {
 			return f, nil
 		}
 	}
-	}
 	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
-}

src/os/exec/lp_windows_test.go

@@ -107,7 +107,7 @@ 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)
+	dirs := filepath.SplitList(PATH)
 	for i := range dirs {
 		dirs[i] = filepath.Join(dir, dirs[i])
 	}