diff --git a/README.md b/README.md
index cd31651..79ba459 100644
--- a/README.md
+++ b/README.md
@@ -207,7 +207,7 @@ It only covers the most common items, and tries to guess sensible defaults.
 Press ^C at any time to quit.
 tool: (go_install) go_build
 Do you want to continue?[y/n] y
-package: (main) github.com/voidint/gbb/build
+importpath: (main) github.com/voidint/gbb/build
 variable: Date
 value: {{.Date}}
 Do you want to continue?[y/n] y
@@ -219,7 +219,7 @@ About to write to /Users/voidint/cloud/workspace/go/lib/src/github.com/voidint/g
 {
     "version": "0.2.0",
     "tool": "go build",
-    "package": "github.com/voidint/gbb/build",
+    "importpath": "github.com/voidint/gbb/build",
     "variables": [
         {
             "variable": "Date",
@@ -261,7 +261,7 @@ commit: db8b606cfc2b24a24e2e09acac24a52c47b68401
 {
     "version": "0.2.0",
     "tool": "go build",
-    "package": "github.com/voidint/gbb/build",
+    "importpath": "github.com/voidint/gbb/build",
     "variables": [
         {
             "variable": "Date",
@@ -289,6 +289,10 @@ commit: db8b606cfc2b24a24e2e09acac24a52c47b68401
 	
 	
 ## changelog
+### 0.4.0 - 
+- `gbb.json`中的配置项`package`重命名为`importpath`。[#9](https://github.com/voidint/gbb/issues/9)
+- 新增命令行选项`--config`用于自定义配置文件路径。[#16](https://github.com/voidint/gbb/issues/16)
+
 ### 0.3.0 - 2017/01/09
 - 若开启debug模式`gbb --debug`，那么变量表达式求值过程详情也一并输出。[#12](https://github.com/voidint/gbb/issues/12) [#6](https://github.com/voidint/gbb/issues/6)
 - 变量表达式首字母大写。[#11](https://github.com/voidint/gbb/issues/11)
diff --git a/tool/builder.go b/tool/builder.go
index 6db72cf..ebe9172 100644
--- a/tool/builder.go
+++ b/tool/builder.go
@@ -35,44 +35,25 @@ func Build(conf *config.Config, dir string) error {
 
 // buildDir 切换到指定工作目录，调用指定的编译工具进行编译。
 func buildDir(conf *config.Config, dir string) (err error) {
-	wd, err := os.Getwd()
-	if err != nil {
+	if err = chdir(dir, conf.Debug); err != nil {
 		return err
 	}
-	if wd != dir {
-		if conf.Debug {
-			fmt.Printf("==> cd %s\n", dir)
-		}
-		if err = os.Chdir(dir); err != nil {
-			return err
-		}
-	}
 
 	cmdArgs := strings.Fields(conf.Tool) // go install ==> []string{"go", "install"}
 
-	var buf bytes.Buffer
-	for i := range conf.Variables {
-		varName := strings.TrimSpace(conf.Variables[i].Variable)
-		varExpr := strings.TrimSpace(conf.Variables[i].Value)
-
-		if conf.Debug {
-			fmt.Printf("==> eval(%q)\n", varExpr)
-		}
-		val, err := variable.Eval(varExpr, conf.Debug)
+	mainPkg, err := isMainPkg(dir)
+	if err != nil {
+		return err
+	}
+	if mainPkg {
+		flags, err := ldflags(conf)
 		if err != nil {
 			return err
 		}
-		if conf.Debug {
-			fmt.Println(val)
-		}
-		buf.WriteString(fmt.Sprintf(`-X "%s.%s=%s"`, conf.Importpath, varName, val))
-		if i < len(conf.Variables)-1 {
-			buf.WriteByte(' ')
+		if flags != "" {
+			cmdArgs = append(cmdArgs, "-ldflags", flags)
 		}
 	}
-	if buf.Len() > 0 {
-		cmdArgs = append(cmdArgs, "-ldflags", buf.String())
-	}
 
 	if conf.Debug {
 		fmt.Print("==> ", cmdArgs[0])
@@ -92,3 +73,42 @@ func buildDir(conf *config.Config, dir string) (err error) {
 	cmd.Stderr = os.Stderr
 	return cmd.Run()
 }
+
+func chdir(dir string, debug bool) (err error) {
+	wd, err := os.Getwd()
+	if err != nil {
+		return err
+	}
+	if wd == dir {
+		return nil
+	}
+
+	if debug {
+		fmt.Printf("==> cd %s\n", dir)
+	}
+	return os.Chdir(dir)
+}
+
+func ldflags(conf *config.Config) (flags string, err error) {
+	var buf bytes.Buffer
+	for i := range conf.Variables {
+		varName := strings.TrimSpace(conf.Variables[i].Variable)
+		varExpr := strings.TrimSpace(conf.Variables[i].Value)
+
+		if conf.Debug {
+			fmt.Printf("==> eval(%q)\n", varExpr)
+		}
+		val, err := variable.Eval(varExpr, conf.Debug)
+		if err != nil {
+			return "", err
+		}
+		if conf.Debug {
+			fmt.Println(val)
+		}
+		buf.WriteString(fmt.Sprintf(`-X "%s.%s=%s"`, conf.Importpath, varName, val))
+		if i < len(conf.Variables)-1 {
+			buf.WriteByte(' ')
+		}
+	}
+	return buf.String(), nil
+}
diff --git a/tool/golang.go b/tool/golang.go
index b8cc721..349727e 100644
--- a/tool/golang.go
+++ b/tool/golang.go
@@ -4,7 +4,6 @@ import (
 	"go/ast"
 	"go/parser"
 	"go/token"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -27,7 +26,7 @@ func NewGoBuilder(conf *config.Config) *GoBuilder {
 
 // Build 切换到指定工作目录后调用编译工具编译。
 func (b *GoBuilder) Build(rootDir string) error {
-	paths, err := walkMainDir(rootDir)
+	paths, err := walkPkgs(rootDir)
 	if err != nil {
 		return err
 	}
@@ -40,7 +39,7 @@ func (b *GoBuilder) Build(rootDir string) error {
 }
 
 // 查找root及其子孙目录下所有的main包路径
-func walkMainDir(rootDir string) (paths []string, err error) {
+func walkMainPkgs(rootDir string) (paths []string, err error) {
 	return paths, filepath.Walk(rootDir, func(path string, info os.FileInfo, e error) error {
 		if e != nil {
 			return e
@@ -92,7 +91,7 @@ func hasMain(srcfile string) (bool, error) {
 	return false, nil
 }
 
-func walkPkgDir(rootDir string) (paths []string, err error) {
+func walkPkgs(rootDir string) (paths []string, err error) {
 	return paths, filepath.Walk(rootDir, func(path string, info os.FileInfo, e error) error {
 		if e != nil {
 			return e
@@ -120,22 +119,45 @@ func walkPkgDir(rootDir string) (paths []string, err error) {
 
 // isGoPkg 判断路径是否是golang的包
 func isGoPkg(path string) (yes bool, err error) {
-	path = strings.TrimSpace(path)
+	// path = strings.TrimSpace(path)
+	// if path == "" {
+	// 	return false, nil
+	// }
+	// infos, err := ioutil.ReadDir(path)
+	// if err != nil {
+	// 	return false, err
+	// }
+
+	// for i := range infos {
+	// 	if infos[i].IsDir() {
+	// 		continue
+	// 	}
+	// 	if ext := filepath.Ext(infos[i].Name()); ext == ".go" { // TODO 排除go test目录
+	// 		return true, nil
+	// 	}
+	// }
+	// return false, nil
+
 	if path == "" {
 		return false, nil
 	}
-	infos, err := ioutil.ReadDir(path)
+	fset := token.NewFileSet()
+	pkgs, err := parser.ParseDir(fset, path, nil, 0)
 	if err != nil {
 		return false, err
 	}
+	return len(pkgs) > 0, nil
+}
 
-	for i := range infos {
-		if infos[i].IsDir() {
-			continue
-		}
-		if ext := filepath.Ext(infos[i].Name()); ext == ".go" { // TODO 排除go test目录
-			return true, nil
-		}
+func isMainPkg(path string) (yes bool, err error) {
+	if path == "" {
+		return false, nil
 	}
-	return false, nil
+	fset := token.NewFileSet()
+	pkgs, err := parser.ParseDir(fset, path, nil, 0)
+	if err != nil {
+		return false, err
+	}
+	_, yes = pkgs["main"]
+	return yes, nil
 }
diff --git a/tool/golang_test.go b/tool/golang_test.go
index 665a5b3..45421f5 100644
--- a/tool/golang_test.go
+++ b/tool/golang_test.go
@@ -32,13 +32,13 @@ func TestHasMain(t *testing.T) {
 	})
 }
 
-func TestWalkMainDir(t *testing.T) {
+func TestWalkMainPkgs(t *testing.T) {
 	Convey("遍历根目录及其子目录查找包含main函数的源代码文件路径", t, func() {
 		dir, err := os.Getwd()
 		So(err, ShouldBeNil)
 		So(strings.HasSuffix(dir, filepath.Join("src", "github.com", "voidint", "gbb", "tool")), ShouldBeTrue)
 		workspace := strings.TrimRight(dir, fmt.Sprintf("%ctool", os.PathSeparator))
-		paths, err := walkMainDir(workspace)
+		paths, err := walkMainPkgs(workspace)
 		So(err, ShouldBeNil)
 		So(paths, ShouldNotBeEmpty)
 		So(len(paths), ShouldEqual, 1)
@@ -46,17 +46,17 @@ func TestWalkMainDir(t *testing.T) {
 	})
 }
 
-func TestWalkPkgDir(t *testing.T) {
+func TestWalkPkgs(t *testing.T) {
 	Convey("查找指定目录及其子目录下所有满足golang包的目录路径", t, func() {
 		wd, err := os.Getwd()
 		So(err, ShouldBeNil)
-		paths, err := walkPkgDir(wd)
+		paths, err := walkPkgs(wd)
 		So(err, ShouldBeNil)
 		So(paths, ShouldNotBeEmpty)
 		So(len(paths), ShouldEqual, 1)
 		So(paths[0], ShouldEqual, wd)
 
-		paths, err = walkPkgDir(strings.TrimRight(wd, "tool"))
+		paths, err = walkPkgs(strings.TrimRight(wd, "tool"))
 		So(err, ShouldBeNil)
 		So(paths, ShouldNotBeEmpty)
 		So(len(paths), ShouldEqual, 7)
@@ -75,7 +75,7 @@ func TestWalkPkgDir(t *testing.T) {
 			})
 			defer monkey.Unpatch(isGoPkg)
 
-			paths, err := walkPkgDir(wd)
+			paths, err := walkPkgs(wd)
 			So(err, ShouldNotBeNil)
 			So(err, ShouldEqual, ErrIsGoPkg)
 			So(paths, ShouldBeEmpty)
@@ -130,3 +130,61 @@ func TestIsGoPkg(t *testing.T) {
 		})
 	})
 }
+
+func TestIsMainPkg(t *testing.T) {
+	Convey("检查指定路径是否是main包", t, func() {
+		wd, err := os.Getwd()
+		So(err, ShouldBeNil)
+		So(wd, ShouldNotBeBlank)
+
+		Convey("合法路径", func() {
+			Convey("非main包且不包含子包", func() {
+				yes, err := isMainPkg(wd)
+				So(err, ShouldBeNil)
+				So(yes, ShouldBeFalse)
+			})
+			Convey("非main包且包含子包", func() {
+				path := filepath.Join(
+					strings.TrimRight(wd, "tool"),
+					"vendor", "github.com", "smartystreets", "assertions",
+				)
+				yes, err := isMainPkg(path)
+				So(err, ShouldBeNil)
+				So(yes, ShouldBeFalse)
+			})
+
+			Convey("main包", func() {
+				yes, err := isMainPkg(strings.TrimRight(wd, "tool"))
+				So(err, ShouldBeNil)
+				So(yes, ShouldBeTrue)
+			})
+		})
+
+		Convey("非法路径", func() {
+			Convey("路径为空", func() {
+				yes, err := isMainPkg("")
+				So(err, ShouldBeNil)
+				So(yes, ShouldBeFalse)
+			})
+			Convey("路径非目录", func() {
+				yes, err := isMainPkg(filepath.Join(wd, "golang_test.go"))
+				So(err, ShouldNotBeNil)
+				So(yes, ShouldBeFalse)
+			})
+			Convey("路径不存在", func() {
+				yes, err := isMainPkg(filepath.Join(wd, "not_exist_dir"))
+				So(err, ShouldNotBeNil)
+				So(yes, ShouldBeFalse)
+			})
+			Convey("路径下不包含go源文件(非包路径)", func() {
+				path := filepath.Join(
+					strings.TrimRight(wd, "tool"),
+					"vendor", "github.com",
+				)
+				yes, err := isMainPkg(path)
+				So(err, ShouldBeNil)
+				So(yes, ShouldBeFalse)
+			})
+		})
+	})
+}