求一正则表达式！

Question

$str="gesget[attachment=3]etrewtre
trewt[attachment=5]wtrewte
trewtret[attachment=17]rewtretrettrewtre[attachment=16]ewtrewt
trewtrew[attachment=10]trewtr";
$pattern="/\[attachment=\d+\]/";
$replacement="<br>";
$str=preg_replace($pattern, $replacement,$str); 
echo $str;

Answer 1

<?php
$str="gesget[attachment=3]etrewtre
trewt[attachment=5]wtrewte
trewtret[attachment=17]rewtretrettrewtre[attachment=16]ewtrewt
trewtrew[attachment=10]trewtr";
$pattern="/\[.+\]/U";
$replacement="<br>";
echo $str=preg_replace($pattern, $replacement,$str);
?>

Answer 2

$str = preg_replace ("|\[attachment=\d+\]|", "<br>",$str);