如何在content-disposition头中preg_match所有三种情况？

Question

I'm trying to decode the content-disposition header (from curl) to get the filename using the following regular expression:

<?php
$str = 'attachment;filename="unnamed.jpg";filename*=UTF-8\'\'unnamed.jpg\'';
preg_match('/^.*?filename=(["\'])([^"\']+)\1/m', $str, $matches);

print_r($matches);

So while it matches if the filename is in single or double quotes, it fails if there are no quotes around the filename (which can happen)

$str = 'attachment;filename=unnamed.jpg;filename*=unnamed.jpg';

Right now I'm using two regular expressions (with if-else) but I just wanted to learn if it is possible to do in a single regex? Just for my own learning to master regex.

Answer 1

I will use the branch reset feature (?|...|...|...) that gives a more readable pattern and avoids to create a capture group for the quotes. In a branch-reset group, each capture groups have the same numbers for each alternative:

if ( preg_match('~filename=(?|"([^"]*)"|\'([^\']*)\'|([^;]*))~', $str, $match) )
    echo $match[1], PHP_EOL;

Whatever the alternative that succeeds, the capture is always in group 1.