function string_to_underscore($string){
    $string = preg_replace('/[\'"]/', '', $string);
    $string = preg_replace('/[^a-zA-Z0-9]+/', '_', $string);
    $string = trim($string, '_');
    $string = strtolower($string);
    return $string;}

Convert string to underscore, for SE safe URLs etc.

string_to_underscore($string)

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PHP