Having problems getting a PHP regex to match

Question

Here is my problem. It's probably a simple fix. I have a regex that I am using to replace a url BBCode. What I have right now that is not working looks like this.

<?php
$input_string = '[url=www.test.com]Test[url]';
$regex = '/\[url=(.+?)](.+?)\[\/url]/is';
$replacement_string = '<a href="$1">$2</a>';
echo preg_replace($regex, $replacement_string, $input_string);
?>

This currently outputs the original $input_string, while I would like it to output the following.

<a href="www.test.com">Test</a>

What am I missing?

Your Reyes is looking for /url yet your demo doesn't include it. Is that a typo? — Brad Christie
– Brad Christie, Commented Jan 1, 2011 at 23:43
What you are missing is that you should not parse structured languages with regular expressions. There are bbcode parsers for PHP available. — Tomalak
– Tomalak, Commented Jan 1, 2011 at 23:43
asside from the fact that there are bbcode PECL extensions available, are there any other reasons that i should not use regex to do this? — dqhendricks
– dqhendricks, Commented Jan 1, 2011 at 23:54
This rather famous answer is the reason - as @Tomalak said, "you should not parse structured languages with regular expressions". If regex works for you in your situation, then it's fine, but regexes aren't generally a robust tool to use to parse "structured languages". — thirtydot
– thirtydot, Commented Jan 1, 2011 at 23:57
The point is, for every sophisticated smug regex you come up with, there will be a comparatively easy attack to knock it over. The problem of parsing bbcode is solved, why do want to roll you own parser? Bit-by-bit your regexes will become bloated, brittle and unmaintainable monsters with every corner case you work into them, and in the end it still won't be 100% safe. Apart from that, in terms if grammar complexity, bbcode is just like HTML, only with square brackets. — Tomalak
– Tomalak, Commented Jan 2, 2011 at 9:14

thirtydot · Accepted Answer · 2011-01-01 23:45:55Z

3

<?php
$input_string = '[url=www.test.com]Test[/url]';
$regex = '/\[url=(.+?)\](.+?)\[\/url\]/is';
$replacement_string = '<a href="$1">$2</a>';
echo preg_replace($regex, $replacement_string, $input_string);
?>

In your BBCode string, I closed the [url] properly.
I escaped a ] in the regex (not sure if that was an actual problem).

Note that [url]http://example.org[/url] is also a valid way to make a link in BBCode.

You should listen to the comments suggesting you use an existing BBCode parser.

answered Jan 1, 2011 at 23:45

thirtydot

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Sujith Surendranathan · Accepted Answer · 2011-01-01 23:41:33Z

0

Change this line as follows: $regex = '/[url=(.+?)](.+?)[url]/is';

OK, the formatting is not proper. While I figure it out, see this: http://pastebin.com/6pF0FEbA

answered Jan 1, 2011 at 23:41

Sujith Surendranathan

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1 Comment

Sujith Surendranathan Over a year ago

Dam*ed backslahes. I posted @ Pastebin. It works, but I could not paste it properly here :-/

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