NSpeaks

Shortcodes and Custom Fields are two very powerful features of Wordpress which allow you to insert any custom content anywhere on your site. But in certain cases, you may need to insert a shortcode into your Custom field. This can happen if a plugin you use only offers shortcodes but you need to insert that shortcode only on a certain portion of the theme (e.g. single.php). Now custom fields can be placed at any place of the theme but Shortcodes only appear in post content. And if you include shortcode directly as a custom field value, it will be displayed as it is without getting parsed. For example, if you insert [youtube]VIDEOURL[/youtube] in your custom field to display youtube’s video (In the Viper Video Tags Plugin), it will show up as [youtube]VIDEOURL[/youtube] instead of the video which is because it does not parse shortcodes. But then Wordpress is too great so don’t worry, since a hack is there which will allow you to parse Shortcodes into your custom fields:

<?php
       $var = apply_filters('the_content', get_post_meta($post->ID, 'Custom Field', $single = true) );
?>

In the above code, instead of directly getting a custom field’s value and displaying, apply the filter ‘the_content’ directly to the retreived custom field’s value. This ensures all post content properties including shortcode are applied to the custom field’s value. And hence the shortcode is parsed in the custom field. Now you can use $var anywhere to show the parsed value of the shortcode.

You will need to apply the filter to all the custom field variables individually.

Updated so that the concept is more clear. Also cleaned up and eased the code.