PHP Syntax with variables

I am using the wordpress shopp plugin to sell products on my site. On my template file, I am using a shopp short code to display a particular category. It looks like this:

<?php shopp('catalog','category','load=true&id=16'); ?>

I would like the number 16 to be changeable, so I have stored the correct dynamic number in a variable as follows:

<?php $shopid = get_field('store_id'); ?>

The Variable $shopid is the correct number that should replace the '16' above. The question is, how do I place a vari开发者_运维百科able in the shopp shortcode? I tried as follows without luck:

<?php shopp('catalog','category','load=true&id=$shopid'); ?>

Any ideas how to pull this off?

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Within single-quoted strings variables are not getting replaced by their values:

Note: Unlike the double-quoted and heredoc syntaxes, variables and escape sequences for special characters will not be expanded when they occur in single quoted strings.

Use double quotes or string concatenation instead:

shopp('catalog','category',"load=true&id=$shopid")
shopp('catalog','category','load=true&id='.$shopid)

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Either

<?php shopp('catalog','category',"load=true&id=$shopid"); ?>

Notice the double quotes. Or:

<?php shopp('catalog','category','load=true&id=' . $shopid); ?>

This is concatenation.