Today only the Gap is offering a free shirt when you purchase a pair of regularly priced jeans or pants in store.
The free item must be of equal or lesser value and does not apply to coats, jackets, vests or blazers.
It is not valid online or at any of the Gap outlet, factory etc.. stores. Just Gap.
You can get the details on the Gap Sale on the Facebook page.

It’s not today only, the FB page says it goes until March 2nd.
For every regularly priced pant you get the top. So I bought two pants (perfect khakis and a pair of black) for 49.50 each and got a free sweater – 34.99 and a free shirt 29.99 (both were on clearance).