diff --git a/common/autoconf/configure b/common/autoconf/configure
index 730f51a0c0f8dd60415af2445b8119efa37d8cc4..636f6e8efdd648de3549e126ce7b7f94870f8249 100644
--- a/common/autoconf/configure
+++ b/common/autoconf/configure
@@ -127,11 +127,11 @@ function shell_quote() {
   if [[ -n "$1" ]]; then
     # Uses only shell-safe characters?  No quoting needed.
     # '=' is a zsh meta-character, but only in word-initial position.
-    if echo "$1" | grep -qE '^[ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789.:,%/+=_-]+$' \
-        && ! echo "$1" | grep -qE '^='; then
+    if echo "$1" | grep '^[ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789\.:,%/+=_-]\{1,\}$' > /dev/null \
+        && ! echo "$1" | grep '^=' > /dev/null; then
       quoted="$1"
     else
-      if echo "$1" | grep -qE "[\'!]"; then
+      if echo "$1" | grep "[\'!]" > /dev/null; then
         # csh does history expansion within single quotes, but not
         # when backslash-escaped!
         local quoted_quote="'\\''" quoted_exclam="'\\!'"