Ignore TMPDIR when run container

kyaml/fn/runtime/container/container.go

@@ -195,7 +195,7 @@ func (c *Filter) getCommand() (string, []string) {
 	// export the local environment vars to the container
 	for _, pair := range os.Environ() {
 		items := strings.Split(pair, "=")
-		if items[0] == "" || items[1] == "" {
+		if items[0] == "" || items[1] == "" || shouldEnvIgnored(items[0]) {
 			continue
 		}
 		args = append(args, "-e", items[0])
@@ -203,3 +203,15 @@ func (c *Filter) getCommand() (string, []string) {
 	a := append(args, c.Image)
 	return "docker", a
 }
+
+// shouldEnvIgnored returns true if the environment variable key should be ignored
+// by the container runtime.
+func shouldEnvIgnored(envKey string) bool {
+	ignoreEnvKey := []string{"TMPDIR"}
+	for _, k := range ignoreEnvKey {
+		if k == envKey {
+			return true
+		}
+	}
+	return false
+}

kyaml/fn/runtime/container/container_test.go

@@ -210,3 +210,20 @@ func TestFilter_ExitCode(t *testing.T) {
 		t.FailNow()
 	}
 }
+
+func TestIgnoreEnv(t *testing.T) {
+	ignoredEnvKey := []string{"TMPDIR"}
+	for _, key := range ignoredEnvKey {
+		os.Setenv(key, "")
+	}
+
+	fltr := Filter{Image: "example.com:version"}
+	_, args := fltr.getCommand()
+	for _, arg := range args {
+		for _, key := range ignoredEnvKey {
+			if arg == key {
+				t.Fatalf("%s should not be exported to container", key)
+			}
+		}
+	}
+}