Question

We’re converting to markdown, before we used an ‘in-house’ system, where both the image links and all data with it (e.g. alt) in another bracket.

For example {IMAGE LINK}[OPTIONAL ALT WITH OTHER DATA]

Now we are moving to markdown, (our data is stored as markdown in the database), I need to convert everything into markdown:

So How can I turn all instances of {LINK}[OPTIONAL DATA] (square brackets not required, so some are just {}) into markdown equivalent:

Basically,

{http://www.youtube.com/image.gif}[this
is optional alt] INTO
![alt](http://www.youtube.com/Image.gif)

I have the following so far, but do I deal with the optional [ALT DATA] tag?

   if (preg_match_all('/\[(.*?)\]/i', $string, $matches, PREG_SET_ORDER)) 
   {


   }

Answer 1

To deal with the optional alt attribute you should use preg_replace_callback. This allows you to test for the existence of the alt attr and add it if necessary.

$str = '
This is an image {http://www.youtube.com/image.gif}[this is optional alt]
This is an image with an alt attribute {http://www.youtube.com/image.gif}
';

echo preg_replace_callback(
    '~{(http://[^s]+)}(?:\[(.*?)\])?~',
    function($m){
        if ( isset( $m[2] ) ) {
            return $img = sprintf( '![%s](%s)', $m[2], $m[1] );
        }
        return $img = sprintf( '(%s)', $m[1] );
    },
    $str
);