Regarding the problem of duplicate items caused by regular expression matching

I encountered such a situation to match, but every time it matched the beginning of a duplicate:

$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;

The result is:

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

You can see that the first result has duplicate matches to two push , what's going on? ?

I don’t know how it happened. I tried various things and then changed it to this:

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

That is, I changed the small brackets into square brackets. The result is:

Array
(
    [0] => push_1113_20150105000052430.txt
)

The reason needs further investigation and is currently unknown, but it must be caused by the difference between () and [].

The above has introduced the problem of duplicate items caused by regular expression matching, including the relevant aspects. I hope it will be helpful to friends who are interested in PHP tutorials.