php conditional regex problem

Question

I'm having a tough time sorthing this out. I'm working with a custom plugin system that presents things like this:

<plugin:class:method var1='hello', var2='yes' />

But, ':method' and the variables do not have to exist - only the 'class' is required. For instace, this should still be ok:

<plugin:class />

The problem I'm having is how to I get the regex to conditionally return things when the method and/or variables do not exist. So far, I can get results when all the pieces exist, but not otherwise - this is where I'm at (struggling on the first conditional):

$f = "/<plugin:(?P<class>\w+)(?(?=^:)?P<method>\w+)\s+(.*)\/>/sUi";

Things are working very well with the following code, it's simply a matter of being able to return all the pieces with the conditionals:

preg_replace_callback($f, array($this, 'processing'), $text);

Hope this makes some sense - and is even possible. Thanks.

You are not designing a regular language. use a parser for context-free grammar (yes, I know some regex parsers support recursion … – but it's not the right tool™ for the job) — knittl
– knittl, Commented Sep 25, 2011 at 19:42

rid · Accepted Answer · 2011-09-25 19:53:48Z

1

The easiest and most maintainable way to do this would be to just get the whole plugin:class:method string with a simple /plugin:\S+/ expression, then explode(':', $string).

So, instead of the code above, you'd have something like:

$f = "/<plugin:(\S+)\s+(.*?)\/>/sUi";
if (preg_match($f, $string, $matches)) {
    $parts = explode($matches[1]);
    if (!in_array('method', $parts))
    {
        // do whatever needs done if "method" is not present
    }
    // ...
}

edited Sep 25, 2011 at 19:53

answered Sep 25, 2011 at 19:42

rid

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4 Comments

telefiend Over a year ago

"most maintable" - I'd like to know more about this. Is it because I'm using PCRE extended thing that's not available in all situations?

rid Over a year ago

@telefiend, I'm saying that this would be maintainable because the code will be very easy to read, understand and extend, than a complicated regular expression that would do the same thing. Added example.

telefiend Over a year ago

I understand that. I have actually done it your way in the past but thought it might be more easy if the regex was more precise in it's output. A problem of style I suppose - good thing to think about.

telefiend Over a year ago

$f = "/<plugin:(\S+)\s+(.*)\/>/sUi"; Final solution, as suggested. Keep it simple. Thanks.

Maverick · Accepted Answer · 2011-09-25 19:42:32Z

0

Shouldn't (?=^:) be (?!:) ?

answered Sep 25, 2011 at 19:42

Maverick

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1 Comment

telefiend Over a year ago

code"/<plugin:(?P<class>\w+)(?(?!:)?P<method>\w+)\s+(.*)\/>/sUi"code - doesn't do the trick.

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