diff --git a/lib/spack/spack/cmd/pkg.py b/lib/spack/spack/cmd/pkg.py
index e4e616db563..b21313cbc49 100644
--- a/lib/spack/spack/cmd/pkg.py
+++ b/lib/spack/spack/cmd/pkg.py
@@ -169,7 +169,9 @@ def pkg_hash(args):
 
 def get_grep(required=False):
     """Get a grep command to use with ``spack pkg grep``."""
-    return exe.which(os.environ.get("SPACK_GREP") or "grep", required=required)
+    grep = exe.which(os.environ.get("SPACK_GREP") or "grep", required=required)
+    grep.ignore_quotes = True  # allow `spack pkg grep '"quoted string"'` without warning
+    return grep
 
 
 def pkg_grep(args, unknown_args):
diff --git a/lib/spack/spack/util/executable.py b/lib/spack/spack/util/executable.py
index afb8bcaa390..b4974fc9b57 100644
--- a/lib/spack/spack/util/executable.py
+++ b/lib/spack/spack/util/executable.py
@@ -31,6 +31,7 @@ def __init__(self, name):
 
         self.default_envmod = EnvironmentModifications()
         self.returncode = None
+        self.ignore_quotes = False
 
         if not self.exe:
             raise ProcessError("Cannot construct executable for '%s'" % name)
@@ -188,7 +189,7 @@ def process_cmd_output(out, err):
 
         fail_on_error = kwargs.pop("fail_on_error", True)
         ignore_errors = kwargs.pop("ignore_errors", ())
-        ignore_quotes = kwargs.pop("ignore_quotes", False)
+        ignore_quotes = kwargs.pop("ignore_quotes", self.ignore_quotes)
         timeout = kwargs.pop("timeout", None)
 
         # If they just want to ignore one error code, make it a tuple.