关于正则表达式匹配导致重复项的问题

$file = 'push_1113_20150105000052430.txt';
$file2 = 'confirm_push_1114_20150105000052430.txt';

preg_match('/^(get|push|admin).*.txt/', $file, $rs);
preg_match('/^confirm.*.txt/', $file2, $rs2);

echo '<pre class="brush:php;toolbar:false">';print_r($rs);
echo '<pre class="brush:php;toolbar:false">';print_r($rs2);

exit;

Array
(
    [0] => push_1113_20150105000052430.txt
    [1] => push
)
<pre class="brush:php;toolbar:false">Array
(
    [0] => confirm_push_1114_20150105000052430.txt
)

preg_match('/^[get|push|admin].*.txt/', $file, $rs);

Array
(
    [0] => push_1113_20150105000052430.txt
)