preg_replace replacement 有关问题

preg_replace replacement 问题
preg_replace("/{\.\.\/}2.*\.htm/ie","12312".base64_encode('\\0'), $this->content);失败 


replacement  怎么拼装 “12312 base64_encode(原先匹配到的内容)",一直拼装不成功


------解决思路----------------------
preg_replace("/{\.\.\/}2.*\.htm/ie","‘12312’.base64_encode('\\0')“, $this->content);