$re = '~/mnt/internal-app/logs/internal-app\.log_2019-08-2[01].*~m';
$str = '/mnt/internal-app/logs/internal-app.log_2019-08-20.log.gz
/mnt/internal-app/logs/internal-app.log_2019-08-21.log.gz
..
..
/mnt/internal-app/logs/internal-app.log_2019-08-25.log.gz';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php