diff --git a/main.go b/main.go
index 34d7b28..cc70728 100644
--- a/main.go
+++ b/main.go
@@ -261,28 +261,28 @@ func readFile(path string) ([]byte, error) {
 	return bytea, nil
 }
 
-func getOptOrEnvOrDefault(optKey, optValue, envKey, defaultValue string) (string, error) {
-	if optKey == "" {
-		return "", fmt.Errorf("optKey is empty")
+func getOptOrEnvOrDefault(optName, optValue, envName, defaultValue string) (string, error) {
+	if optName == "" {
+		return "", fmt.Errorf("optName is empty")
 	}
 
 	if optValue != "" {
-		log.Println("use option: " + optKey + "=" + optValue)
+		log.Println("use option value: -" + optName + "=" + optValue)
 		return optValue, nil
 	}
 
-	envValue := os.Getenv(envKey)
+	envValue := os.Getenv(envName)
 	if envValue != "" {
-		log.Println("use env: " + envKey + "=" + envValue)
+		log.Println("use environment variable: " + envName + "=" + envValue)
 		return envValue, nil
 	}
 
 	if defaultValue != "" {
-		log.Println("use default: " + optKey + "=" + defaultValue)
+		log.Println("use default option value: -" + optName + "=" + defaultValue)
 		return defaultValue, nil
 	}
 
-	return "", fmt.Errorf("set option -%s, or set environment variable %s", optKey, envKey)
+	return "", fmt.Errorf("set option -%s, or set environment variable %s", optName, envName)
 }
 
 func capitalizeInitial(s string) (capitalized string) {
diff --git a/main_test.go b/main_test.go
index c954c49..6b78f78 100644
--- a/main_test.go
+++ b/main_test.go
@@ -32,9 +32,9 @@ const (
 	testProbablyExistsPath           = "go.mod"
 
 	// getOptOrEnvOrDefault
-	testOptKey       = "testOptKey"
+	testOptName      = "test-opt-key"
 	testOptValue     = "testOptValue"
-	testEnvKey       = "TEST_ENV_KEY"
+	testEnvName      = "TEST_ENV_KEY"
 	testEnvValue     = "testEnvValue"
 	testDefaultValue = "testDefaultValue"
 
@@ -286,7 +286,7 @@ func Test_readFile_NG_2(t *testing.T) {
 }
 
 func Test_getOptOrEnvOrDefault_OK_1(t *testing.T) {
-	v, err := getOptOrEnvOrDefault(testOptKey, testOptValue, testEnvKey, testDefaultValue)
+	v, err := getOptOrEnvOrDefault(testOptName, testOptValue, testEnvName, testDefaultValue)
 	if err != nil {
 		t.Error(err)
 	}
@@ -295,24 +295,24 @@ func Test_getOptOrEnvOrDefault_OK_1(t *testing.T) {
 	}
 }
 func Test_getOptOrEnvOrDefault_OK_2(t *testing.T) {
-	if err := os.Setenv(testEnvKey, testEnvValue); err != nil {
+	if err := os.Setenv(testEnvName, testEnvValue); err != nil {
 		t.Error(err)
 	}
-	v, err := getOptOrEnvOrDefault(testOptKey, testEmptyString, testEnvKey, testDefaultValue)
+	v, err := getOptOrEnvOrDefault(testOptName, testEmptyString, testEnvName, testDefaultValue)
 	if err != nil {
 		t.Error(err)
 	}
 	if v != testEnvValue {
 		t.Error(err)
 	}
-	if err := os.Unsetenv(testEnvKey); err != nil {
+	if err := os.Unsetenv(testEnvName); err != nil {
 		t.Error(err)
 	}
 
 }
 
 func Test_getOptOrEnvOrDefault_OK_3(t *testing.T) {
-	v, err := getOptOrEnvOrDefault(testOptKey, testEmptyString, testEnvKey, testDefaultValue)
+	v, err := getOptOrEnvOrDefault(testOptName, testEmptyString, testEnvName, testDefaultValue)
 	if err != nil {
 		t.Error(err)
 	}
@@ -332,7 +332,7 @@ func Test_getOptOrEnvOrDefault_NG_1(t *testing.T) {
 }
 
 func Test_getOptOrEnvOrDefault_NG_2(t *testing.T) {
-	v, err := getOptOrEnvOrDefault(testOptKey, testEmptyString, testEnvKey, testEmptyString)
+	v, err := getOptOrEnvOrDefault(testOptName, testEmptyString, testEnvName, testEmptyString)
 	if err == nil {
 		t.Error(err)
 	}