regex - Compilation failed: assertion expected at offset 6

Question

I'm trying to use Casimir et Hippolyte's pattern (Here) to wrap HTML tags in string.

$html = <<<EOD
    $str
EOD;

    $pattern = <<<'EOD'
    ~
    (?(DEFINE)
        (?<self>    < [^\W_]++ [^>]* > )
        (?<comment> <!-- (?>[^-]++|-(?!->))* -->)
        (?<cdata>   \Q<![CDATA[\E (?>[^]]++|](?!]>))* ]]> )
        (?<text>    [^<]++ )
        (?<tag>
            < ([^\W_]++) [^>]* >
            (?> \g<text> | \g<tag> | \g<self> | \g<comment> | \g<cdata> )*
            </ \g{-1} >
        )
    )
    # main pattern
    (?: \g<tag> | \g<self> | \g<comment> | \g<cdata> )+
    ~x
EOD;

After implementing this method, I got an error Compilation failed: assertion expected after (?( at offset 6. What's wrong with this pattern?

I thought you're not there.I've checked phpinfo and this is everything about pcre `PCRE (Perl Compatible Regular Expressions) Support enabled PCRE Library Version 6.6 06-Feb-2006`. — Lewis, Apr 04 '14 at 18:47
Ok, it's a know bug for pcre version <7.2, I will post an other solution (assuming that the DEFINE syntax is the problem). — Casimir et Hippolyte, Apr 04 '14 at 18:55

Casimir et Hippolyte · Accepted Answer · 2014-04-04T19:17:30.943

1

After some researches, it seems that PCRE versions < 7.2 have this kind of bug with the DEFINE syntax.

You can write the same pattern like that:

$pattern = <<<'EOD'
~
(?:
    (?<tag>
            < ([^\W_]++) [^>]* >
            (?> (?<text> [^<]++ )
              | \g<tag>
              | (?<self> < [^\W_]++ [^>]* > )
              | (?<comment> <!-- (?>[^-]++|-(?!->))* -->)
              | (?<cdata> \Q<![CDATA[\E (?>[^]]++|](?!]>))* ]]>)
            )*
            </ \g{2} > # second group from pattern start (<tag> is 1st)
    )
  | \g<self> | \g<comment> | \g<cdata>
)+
~x
EOD;

edited Apr 04 '14 at 19:17

answered Apr 04 '14 at 18:57

Casimir et Hippolyte

88,009
5
94
125

Should I use this or upgrade the PCRE version? Which one is better? Thank you. – Lewis Apr 04 '14 at 18:59
I think upgrading your php version is a good idea, you are probably using a PHP version < 5.3? – Casimir et Hippolyte Apr 04 '14 at 19:03
It is not so old. You can try the 5.4.6 or more recent, as you like. – Casimir et Hippolyte Apr 04 '14 at 19:06
I'll try it. Thank you for your enthusiasm. – Lewis Apr 04 '14 at 19:08

regex - Compilation failed: assertion expected at offset 6

1 Answers1

Linked