If I purchase a stock the day before ex-dividend can I sell it on the ex-dividend date and still get the div?

A buy transaction on the day before X-date will settle the day before the record date, therefore you will own the stock own record date.

A buy on the X-date will settle on the record date, thus the buyer owns the stock on the date of record, a sell transaction will also settle on the record date therefore they will not be the owner on the record day

Keep in mind that on X-date, the price of the stock is reduced by the amount of the dividend.
The stock can trade higher than the dividend and you could make money but you will have to trade sufficient shares to make the trade profitable to cover the cost of both transactions
AND most importantly, all purchases must be paid in full  before they can be sold if not your account will be restricted for 90 days or until payment is made in full and you can not use the proceeds of the sale to cover the purchase.