Hello, have you looked into using an app like SMSBump. I believe one of its functions is link shortening. Or as an alternative you could copy the long link into something like Bitly.com and get a shortened link to use in the message, but that's something you would have to do for each message.
Thanks! To clarify, we're looking for a way to automatically shorten URLS that are generated by Shopify during the order/checkout process, so that when a customer receives SMS confirmation, they get a tidy and short URL. This would help save characters + creates nicer CX