PHP preg_match_all not working on large data

Question

Why is preg_match_all not working?

$pattern = '/\{(?:[^{}]|(?R))*\}/';

$result = 161240 characters

       if (preg_match_all($pattern, $result, $matches)) {
            echo 'Success';
        } else {
            echo 'Not working';
        }

This Displays: "Not working"

Did you check the type of encoding? If there are spaces they will be considered "other character". More, we need the pattern to understand what is going on. — Optiroot, May 16 '18 at 07:09
https://stackoverflow.com/questions/4180910/php-preg-match-all-fails-on-long-strings,: https://stackoverflow.com/questions/11315879/php-preg-match-all-100-mb-file — Pradeep, May 16 '18 at 07:12
@pradeep thanks. i saw that already but is there a way to change it to htaccess? — Mark D, May 16 '18 at 07:13
Try to set a php configuration option like in this question: https://stackoverflow.com/questions/18296441/maximum-length-of-string-preg-match-all-can-match-and-acquire — TiTnOuK, May 16 '18 at 07:15
What if `preg_match_all` returns `0` which means nothing found. It returns `FALSE` if it fails. — Kerkouch, May 16 '18 at 07:16
`if (preg_match_all($pattern, $result, $matches) === FALSE){/* FAILED */}` — Kerkouch, May 16 '18 at 07:27
@wp78de actually i use this to get the value of curl_exec to encode it to json data — Mark D, May 16 '18 at 07:36
@MarkD the subject `$result` is too long, try to cut it, and then try again. — Kerkouch, May 16 '18 at 07:46

score 0 · Accepted Answer · answered May 16 '18 at 07:50

The pattern at play matches balanced curly brackets using regex recursion. The pattern itself looks fine and works as intended.

<?php
$re = '/{(?>[^{}]|(?R))*\}/m';
$str = 'Why is preg_match_all not working?{{{{{
$pattern = \'/\\{(?:[^{}]|(?R))*\\}/\';
$result = 161240 characters
       if (preg_match_all($pattern, $result, $matches)){ {
            echo \'Success\';
        } else {
            echo \'Not working\';
        }
}}}}}}{}{}{}{}{}{}{}{{{{{{}}}}}';

//preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
if (preg_match_all($re, $str, $matches)) {
echo 'Success\n';
} else {
echo 'Not working\n';
}

// Print the entire match result
var_dump($matches);

This also works with larger input (here tested with ~5000 characters). The most likely explanation is: the pattern does not find a valid match.

However, you are running a recursive regex on a very large input string. Many, things could go wrong. The PCRE engine reaches internal limits, your string is not properly encoded, timeouts, etc.

PHP preg_match_all not working on large data

1 Answers1