diff --git a/stack_orchestrator/deploy/k8s/helpers.py b/stack_orchestrator/deploy/k8s/helpers.py
index 814848d4..1fe697e7 100644
--- a/stack_orchestrator/deploy/k8s/helpers.py
+++ b/stack_orchestrator/deploy/k8s/helpers.py
@@ -17,6 +17,7 @@ from kubernetes import client
 import os
 from pathlib import Path
 import subprocess
+import re
 from typing import Set, Mapping, List
 
 from stack_orchestrator.opts import opts
@@ -220,9 +221,16 @@ def merge_envs(a: Mapping[str, str], b: Mapping[str, str]) -> Mapping[str, str]:
     return result
 
 
-# DANGER: implement me
 def _expand_shell_vars(raw_val: str) -> str:
-    return raw_val
+    # could be: <string> or ${<env-var-name>} or ${<env-var-name>:-<default-value>}
+    # TODO: implement support for variable substitution and default values
+    # if raw_val is like ${<something>} print a warning and substitute an empty string
+    # otherwise return raw_val
+    match = re.search(r"^\$\{(.*)\}$", raw_val)
+    if match:
+        print(f"WARNING: found unimplemented environment variable substitution: {raw_val}")
+    else:
+        return raw_val
 
 
 # TODO: handle the case where the same env var is defined in multiple places