phenomax · June 5, 2016 08:30 · Jun 5, 2016
diff --git a/regex.php b/regex.php
@@ -0,0 +1,20 @@
+/**
+ * @param $str the string to check
+ * @return bool whether the String $str is a valid ip or not
+ */
+function isValidIP($str)
+{
+    /**
+     * Alternative solution using filter_var
+     *
+     * return (bool)filter_var($str, FILTER_VALIDATE_IP);
+     */
+
+    /**
+     * Normally preg_match returns "1" when there is a match between the pattern and the provided $str.
+     * By casting it to (bool), we ensure that our result is a boolean.
+     * This regex should validate every IPv4 addresses, which is no local adress (e.g. 127.0.0.1 or 192.168.2.1).
+     * This pattern was debugged using https://regex101.com/
+     */
+    return (bool)preg_match('^(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)(?:[.](?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)){3}$', $str);
+}