Adding comma after variants (product description)

The situation: Features have more than one variant

my aspiration: putting a comma after each feature besides the last one.

an example would be; style: Vintage, Antique, Random feature

File to edit is the product_features.tpl.

this is the code which i currently have and is in need of modification.

{elseif $feature.feature_type == "S"}
{foreach from=$feature.variants item="var"}
{if $var.selected}{$var.variant}, {/if}

if anyone can help me I would appreciate it after trying to figure this out for over an hour.