- var_dump: documentation ( source)
- array_flip: documentation ( source)
- preg_grep: documentation ( source)
<?php
$a = [
'net_sec1' => 'a',
'net_sec2' => 'b',
'net_sec3' => 'c',
'ss_ks_kw' => 'a',
];
$aa = preg_grep(
'/^net_sec(\d+)$/',
array_flip($a)
);
var_dump($aa);