$string="dfdLiverpool fans club好dfs";
     $pat1="|(\[url=)";
     $pat2="([^]]+)";
     $pat3="(\])";
     $pat4="(.+?)";
     $pat5="(\[/url\])|is";
     $pattern="$pat1$pat2$pat3$pat4$pat5";
     $replacement=preg_replace($pattern,"<a href=\\2>\\4</a>",$string);