Extracting fulldate from yyyy-m-dd?

i've got 100s of files with names like:

 CPC_2001_5_21_7.pdf
 CPC_YYYY_M_DD_7.pdf

The last number is a page number and its irrel开发者_StackOverflow中文版evant. I want to sort them out into directories like:

YYYYMMDD (ie: 20010521)

You can extract the year, month and day with:

if (preg_match('/^CPC_(\d{4})_(\d{1,2})_(\d{1,2}).*$/', $filename, $matches)) {
    list($file, $year, $month, $day) = $matches;
}

If I were you, I would use the heavenly DateTime::createFromFormat. This allows you to designate a pattern and create a DateTime object from it.

So, for example,

$date = 'CPC_2001_5_21_7.pdf';
$dt = DateTime::createFromFormat('!*Y_n_d_*.*', $date);

You can then build a string with the data you want:

$filename = $dt->format('Ymd') . '.pdf';

You should split by underscore, then format the new filename using nullpadding.

<?php
    $filenames = array(
        "CPC_2001_5_21_7.pdf",
        "CPC_2002_2_13_7.pdf",
        "CPC_2004_6_23_7.pdf"
    );
    $newfilenames = array();

    foreach($filenames as $filename)
    {
        $split = explode("_", $filename);

        $newfilenames[] = sprintf("%04s%02s%02s", $split[1], $split[2], $split[3]) . ".pdf";
    }

    print_r($newfilenames);
?>

outputs

Array
(
    [0] => 20010521.pdf
    [1] => 20020213.pdf
    [2] => 20040623.pdf
)