fix linter issue

kyaml/fn/runtime/container/container.go

@@ -162,6 +162,8 @@ func (c *Filter) setupExec() {
 	c.Exec.Args = args
 }
 
+var tmpDirEnvKey string = "TMPDIR"
+
 // getArgs returns the command + args to run to spawn the container
 func (c *Filter) getCommand() (string, []string) {
 	// run the container using docker.  this is simpler than using the docker
@@ -197,7 +199,7 @@ 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] == "" || items[0] == "TMPDIR" {
+		if items[0] == "" || items[1] == "" || items[0] == tmpDirEnvKey {
 			continue
 		}
 		args = append(args, "-e", items[0])

kyaml/fn/runtime/container/container_test.go

@@ -106,7 +106,7 @@ metadata:
 			for _, e := range os.Environ() {
 				// the process env
 				parts := strings.Split(e, "=")
-				if parts[0] == "" || parts[1] == "" || parts[0] == "TMPDIR" {
+				if parts[0] == "" || parts[1] == "" || parts[0] == tmpDirEnvKey {
 					continue
 				}
 				tt.expectedArgs = append(tt.expectedArgs, "-e", parts[0])
@@ -212,13 +212,13 @@ func TestFilter_ExitCode(t *testing.T) {
 }
 
 func TestIgnoreEnv(t *testing.T) {
-	os.Setenv("TMPDIR", "")
+	os.Setenv(tmpDirEnvKey, "")
 
 	fltr := Filter{Image: "example.com:version"}
 	_, args := fltr.getCommand()
 	for _, arg := range args {
-		if arg == "TMPDIR" {
-			t.Fatalf("TMPDIR should not be exported to container")
+		if arg == tmpDirEnvKey {
+			t.Fatalf("%s should not be exported to container", tmpDirEnvKey)
 		}
 	}
 }