preg_replace_callback error

Question

I'm using the following code on my WordPress install:

function add_glossary_links($content) {
    global $wpdb, $wordlist;
    if ( !$wordlist && !$wordlist = get_option('wordlist') ) {
        mysql_query('SET SESSION group_concat_max_len = 100000');
        $wordlist = $wpdb->get_var('SELECT GROUP_CONCAT(DISTINCT post_title SEPARATOR "|") AS list FROM '.$wpdb->posts.' WHERE post_status="publish" AND post_type="glossary" AND post_parent>0');
        add_option('wordlist', $wordlist);
    }

    $wordlist = str_replace(array(" ", "'", "."), array("\s", "\'", "\."), $wordlist);
    echo $wordlist;

    $content = preg_replace_callback(
        '/\b('.$wordlist.')\b/i',
        create_function(
            '$matches',
            'return "<a href=\"/glossary/" . strtolower(substr($matches[0],0,1) . "/" . $matches[0]) . "/\">" . $matches[0] . "</a>";'
        ),
        $content
    );

    return preg_replace('/(<[^<]+)<a\s.*?>(.*?)<\/a>/si','$1$2', $content);
}

add_filter( 'the_content', 'add_glossary_links' );

The idea is that I get a list of words from my database; if they exist I replace them with links to the appropriate glossary term.

$wordlist is echoing out as this: http://pastebin.com/6XnWBJwM

The error that I'm receiving is this:

Warning: preg_replace_callback(): Unknown modifier 'c' in /my.website/wp-content/themes/mytheme/functions.php on line 384

Line 384 is the last line of this segment:

$content = preg_replace_callback(
        '/\b('.$wordlist.')\b/i',
        create_function(
            '$matches',
            'return "<a href=\"/glossary/" . strtolower(substr($matches[0],0,1) . "/" . $matches[0]) . "/\">" . $matches[0] . "</a>";'
        ),
        $content
    );

I presume there's a problem with the formatting of the regexp and the way the wordlist is displaying but I can't for the life of me fathom it.

Thanks in advance,

Niet the Dark Absol · Accepted Answer · 2012-02-15 22:51:21Z

1

You are getting this error because one of the words has a / in it, which is being interpreted as the end delimiter. Anything after is then interpreted as modifiers, and "c" isn't valid as one of those.

You should run the input through preg_quote(), however since you are concatenating the values in your query this won't work out of the box.

I suggest not using GROUP_CONCAT, instead getting each word on its own row. Then, take the rows and fill an array with the words. Last, use implode("|",array_map("preg_quote",$words,array_fill(0,count($words),"/"))) and put that in your regex.

edited Feb 15, 2012 at 22:51

answered Feb 15, 2012 at 22:44

Niet the Dark Absol

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5 Comments

alex Over a year ago

Note that preg_quote() without the second argument won't escape /.

turbonerd Over a year ago

I'm using GROUP_CONCAT because it was suggested to me for speed purposes - the list is derived from 1,750 rows in the database. Is there any other way around it without changing the SQL?

Niet the Dark Absol Over a year ago

Well, you could just use str_replace("/","\\/",$wordlist), but bear in mind that you leave yourself open to injection if any of those words can be user-submitted (or any of them contain other regex-specific characters)

turbonerd Over a year ago

Glossary entries are written by author-level users in the admin area. Could I sanitise the data before it goes into the database, then run a str_replace as you're suggesting? Is there a list of other regex characters that would need escaping? Any idea what kind of speed impact a str_replace would have on ~1700 entries?

Niet the Dark Absol Over a year ago

You can certainly run preg_quote on input data before it gets saved, yes. I would suggest running a single-use code that takes all the words, runs them through preg_quote, then puts the result back in the database.

alex · Accepted Answer · 2012-02-15 22:47:53Z

1

You should run $wordlist through preg_quote().

$safeWordlist = implode('|', 
                    array_map(function($word) { return preg_quote($word, '/'); }, 
                    explode('|', $wordlist))
                       );

CodePad.

Don't roll your own escaping method :)

edited Feb 15, 2012 at 22:47

answered Feb 15, 2012 at 22:41

alex

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3 Comments

turbonerd Over a year ago

Hi Alex. Yeah I meant to remove the str_replace as it was just me mucking about trying to fix things. Will your code have an impact on speed when used with ~1750 entries in the array?

alex Over a year ago

@dunc Possibly. You should also watch for the limit of the regular expression. It's limited to 65k from memory.

turbonerd Over a year ago

Any suggestions as to how I can get around this then? It needs to be as quick as possible really. More information available from my OP on WPSE: wordpress.stackexchange.com/questions/41667

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