diff --git a/merlin/main.py b/merlin/main.py
index 8b23b7f08..2151eed46 100644
--- a/merlin/main.py
+++ b/merlin/main.py
@@ -127,7 +127,9 @@ def parse_override_vars(variables_list):
                 )
             key = entry[0]
             if key is None or key == "" or "$" in key:
-                raise ValueError("--vars requires valid variable names.")
+                raise ValueError(
+                    "--vars requires valid variable names comprised of alphanumeric characters and underscores."
+                )
             if key in RESERVED:
                 raise ValueError(
                     f"Cannot override reserved word '{key}'! Reserved words are: {RESERVED}."
diff --git a/merlin/spec/expansion.py b/merlin/spec/expansion.py
index ef5999571..eadd21c65 100644
--- a/merlin/spec/expansion.py
+++ b/merlin/spec/expansion.py
@@ -41,6 +41,10 @@
     error_override_vars,
 )
 from merlin.spec.specification import MerlinSpec
+from merlin.utils import (
+    contains_shell_ref,
+    contains_token,
+)
 
 
 MAESTRO_RESERVED = {"SPECROOT", "WORKSPACE", "LAUNCHER"}
@@ -74,7 +78,7 @@ def var_ref(string):
     by $(<str>).
     """
     string = string.upper()
-    if "$(" in string:
+    if contains_token(string):
         LOG.warning(f"Bad var_ref usage on string '{string}'.")
         return string
     return f"$({string})"
@@ -86,7 +90,7 @@ def expand_line(line, var_dict):
     and user variables, as well as variables in 'var_dict'.
     """
     line = expandvars(expanduser(line))
-    if "$" not in line:
+    if not contains_token(line):
         return line
     for key, val in var_dict.items():
         line = line.replace(var_ref(key), str(val))
@@ -133,14 +137,14 @@ def determine_user_variables(*user_var_dicts):
                 f"Cannot reassign value of reserved word '{key}'! Reserved words are: {RESERVED}."
             )
         new_val = str(val)
-        if "$(" in new_val:  # change to re
+        if contains_token(new_val):
             for determined_key in determined_results.keys():
                 var_determined_key = var_ref(determined_key)
                 if var_determined_key in new_val:
                     new_val = new_val.replace(
                         var_determined_key, determined_results[determined_key]
                     )
-        if "$" in new_val:  # change to re
+        if contains_shell_ref(new_val):
             new_val = expandvars(new_val)
         determined_results[key.upper()] = new_val
     return determined_results
diff --git a/merlin/spec/specification.py b/merlin/spec/specification.py
index 1275b5572..9221d2af6 100644
--- a/merlin/spec/specification.py
+++ b/merlin/spec/specification.py
@@ -36,17 +36,17 @@
 import json
 import logging
 import os
-from io import StringIO
 from contextlib import suppress
+from io import StringIO
 
 import jsonschema
 import yaml
 from maestrowf.specification.yamlspecification import YAMLSpecification
 
 from merlin.spec import (
+    SCHEMA_PATH,
     all_keys,
     defaults,
-    SCHEMA_PATH
 )
 
 
@@ -222,7 +222,7 @@ def get_worker_names(self):
         for worker in self.merlin["resources"]["workers"]:
             result.append(worker)
         return result
-    
+
     def verify(self):
         """Validate the specification."""
 
@@ -237,7 +237,9 @@ def verify(self):
         super().validate_schema("env", self.environment, schemas["ENV"])
         super().validate_schema("batch", self.batch, schemas["BATCH"])
         for step in self.study:
-            super().validate_schema(f"study step {step['name']}", step, schemas["STUDY_STEP"])
+            super().validate_schema(
+                f"study step {step['name']}", step, schemas["STUDY_STEP"]
+            )
         for param, contents in self.globals.items():
             super().validate_schema("global.params", contents, schemas["PARAM"])
 
diff --git a/merlin/study/study.py b/merlin/study/study.py
index f73577985..ade49cb7f 100644
--- a/merlin/study/study.py
+++ b/merlin/study/study.py
@@ -52,6 +52,7 @@
 from merlin.spec.specification import MerlinSpec
 from merlin.study.dag import DAG
 from merlin.utils import (
+    contains_token,
     get_flux_cmd,
     load_array_file,
 )
@@ -353,7 +354,7 @@ def expanded_spec(self):
         )
 
         # expand provenance spec filename
-        if "$(" in self.spec.name:
+        if contains_token(self.spec.name):
             expanded_name = result.description["name"].replace(" ", "_") + ".yaml"
             expanded_workspace = os.path.join(
                 self.output_path,
diff --git a/merlin/utils.py b/merlin/utils.py
index 62c7f3956..54d9cb526 100644
--- a/merlin/utils.py
+++ b/merlin/utils.py
@@ -439,3 +439,22 @@ def check_machines(machines):
             return True
 
     return False
+
+
+def contains_token(string):
+    """
+    Return True if given string contains a token of the form $(STR).
+    """
+    if re.search(r"\$\(\w+\)", string):
+        return True
+    return False
+
+
+def contains_shell_ref(string):
+    """
+    Return True if given string contains a shell variable reference
+    of the form $STR or ${STR}.
+    """
+    if re.search(r"\$\w+", string) or re.search(r"\$\{\w+\}", string):
+        return True
+    return False
diff --git a/tests/integration/run_tests.py b/tests/integration/run_tests.py
index 671795439..ccd4cbef5 100644
--- a/tests/integration/run_tests.py
+++ b/tests/integration/run_tests.py
@@ -411,7 +411,10 @@ def define_tests():
         ),
         "local format 0": (
             f"merlin -lvl debug run {dev_examples}/full_format.yaml --local",
-            [RegexCond("Spec verified. No errors found."), RegexCond("Merlin block verified. No errors found.")],
+            [
+                RegexCond("Spec verified. No errors found."),
+                RegexCond("Merlin block verified. No errors found."),
+            ],
             "local",
         ),
         "local format 1": (