- var_dump: documentation ( source)
- preg_match: documentation ( source)
- preg_quote: documentation ( source)
<?php
$compare = '\d';
$value = 12345;
$pattern = preg_quote($compare);
var_dump( (bool) preg_match('~'.$pattern.'~iu', $value) );
var_dump( (bool) preg_match('~\\'.$compare.'~iu', $value) );
var_dump( (bool) preg_match('~\\d~iu', $value) );