Camel case to underscore

camelCaseToUnderscore.php

    /**
     * Return the underscored version of a CamelCase string.
     *
     * @return string
     */
    function camelCaseToUnderscore($camelCaseString)
    {
        return ltrim(
            strtolower(
                preg_replace(
                    ["/([A-Z]+)/", "/_([A-Z]+)([A-Z][a-z])/"],
                    ["_$1", "_$1_$2"],
                    trim($camelCaseString)
                )
            ),
            '_'
        );
    }