Move quoting to else block only for valid vars. Add test case.

provisioner/shell/provisioner.go

@@ -170,20 +170,17 @@ func (p *Provisioner) Prepare(raws ...interface{}) error {
 	}
 
 	// Do a check for bad environment variables, such as '=foo', 'foobar'
-	for _, kv := range p.config.Vars {
+	for idx, kv := range p.config.Vars {
 		vs := strings.SplitN(kv, "=", 2)
 		if len(vs) != 2 || vs[0] == "" {
 			errs = packer.MultiErrorAppend(errs,
 				fmt.Errorf("Environment variable not in format 'key=value': %s", kv))
+		} else {
+			// Single quote env var values
+			p.config.Vars[idx] = fmt.Sprintf("%s='%s'", vs[0], vs[1])
 		}
 	}
 
-	// Single quote env var values
-	for key := range p.config.Vars {
-		vs := strings.SplitN(p.config.Vars[key], "=", 2)
-		p.config.Vars[key] = fmt.Sprintf("%s='%s'", vs[0], vs[1])
-	}
-
 	if p.config.RawStartRetryTimeout != "" {
 		p.config.startRetryTimeout, err = time.ParseDuration(p.config.RawStartRetryTimeout)
 		if err != nil {

provisioner/shell/provisioner_test.go

@@ -199,3 +199,21 @@ func TestProvisionerPrepare_EnvironmentVars(t *testing.T) {
 		t.Fatalf("should not have error: %s", err)
 	}
 }
+
+func TestProvisionerQuote_EnvironmentVars(t *testing.T) {
+	config := testConfig()
+
+	config["environment_vars"] = []string{"keyone=valueone", "keytwo=value\ntwo"}
+	p := new(Provisioner)
+	p.Prepare(config)
+
+	expectedValue := "keyone='valueone'"
+	if p.config.Vars[0] != expectedValue {
+		t.Fatalf("%s should be equal to %s", p.config.Vars[0], expectedValue)
+	}
+
+	expectedValue = "keytwo='value\ntwo'"
+	if p.config.Vars[1] != expectedValue {
+		t.Fatalf("%s should be equal to %s", p.config.Vars[1], expectedValue)
+	}
+}