$a = '【2019】';
$b = '【';
$c = '】';
echo GetBetween($a,$b,$c);
//输出 2019
public function GetBetween($content,$start,$end){
$r = explode($start, $content);
if (isset($r[1])){
$r = explode($end, $r[1]);
return $r[0];
}
return '';
}