don't recheck runtime architecture

This patch reduces the number of calls to the OS's `arch` to one.
There's a good chance that the CPU architecture doesn't change while the
program is running.

cmd/build.go

@@ -28,7 +28,7 @@ var buildCmd = &cobra.Command{
 		extraMockArgs := impl.MockExtraCmdlineArgs{
 			NoCheck: noCheck,
 		}
-		return impl.Build(repo, pkg, defaultArch(), extraCreateSrpmArgs, extraMockArgs)
+		return impl.Build(repo, pkg, defaultArch, extraCreateSrpmArgs, extraMockArgs)
 	},
 }
 

cmd/common.go

@@ -9,14 +9,14 @@ import (
 	"strings"
 )
 
-func defaultArch() string {
+var defaultArch = func() string {
 	var output []byte
 	var err error
 	if output, err = exec.Command("arch").Output(); err != nil {
 		panic(err)
 	}
 	return strings.TrimRight(string(output), "\n")
-}
+}()
 
 // SetViperDefaults sets defaults for viper configs
 func SetViperDefaults() {

cmd/mock.go

@@ -34,7 +34,7 @@ var mockCmd = &cobra.Command{
 func init() {
 	mockCmd.Flags().StringP("repo", "r", "", "Repository name (OPTIONAL)")
 	mockCmd.Flags().StringP("package", "p", "", "package name (OPTIONAL)")
-	mockCmd.Flags().StringP("target", "t", defaultArch(), "target architecture for the rpmbuild (OPTIONAL)")
+	mockCmd.Flags().StringP("target", "t", defaultArch, "target architecture for the rpmbuild (OPTIONAL)")
 	mockCmd.Flags().Bool("only-create-cfg", false, "Just create mock configuration, don't run mock (OPTIONAL)")
 	mockCmd.Flags().Bool("nocheck", false, "Pass --nocheck to rpmbuild (OPTIONAL)")
 	rootCmd.AddCommand(mockCmd)

cmd/mock_test.go

@@ -29,7 +29,7 @@ func runMockAndVerify(t *testing.T, destDir string,
 	quiet bool,
 	expectedFiles []ExpectedRpmFile,
 	expectedTags map[string]string) {
-	args := []string{"mock", "--target", defaultArch(), "--repo", repoName}
+	args := []string{"mock", "--target", defaultArch, "--repo", repoName}
 	testutil.RunCmd(t, rootCmd, args, quiet, true)
 	for _, expectedFile := range expectedFiles {
 		fileAbsPath := filepath.Join(destDir, "RPMS",