diff --git a/tools/append_or_replace b/tools/append_or_replace
index 47d7095..fdd2736 100755
--- a/tools/append_or_replace
+++ b/tools/append_or_replace
@@ -10,7 +10,7 @@ REGEX=$1
 STRING=$2
 FILE=$3
 
-if ! grep -Eq "$REGEX" "$FILE"; then
+if ! grep -Pq "$REGEX" "$FILE"; then
 	builtin echo -e "$STRING" >>"$FILE"
 	echo 'appended'
 else