$v = array('vv','bb'); $str = "vv,cc,abcde,www.111cn.net,vv"; $str=preg_replace("/$v[0]/","".$v[0]."",$str,1); echo $str; //bb,cc,abcde,www.111cn.net,vv
$str=preg_replace("/$v[0]/","".$v[0]."",$str,2); //bb,cc,abcde,www.111cn.net,bb