Yes, you have to file a tax return to get the stimulus.
"In essence, the 2 stimulus checks act as an advance of your 2020 income tax refund. This means when you prepare your 2020 income tax return, there will be a line to include the section 6428 credit (line 30 on the 2020 form 1040). The credit on your 2020 return is subtracted by any amount received as a stimulus check in 2020. If the amount you received as a stimulus check is less than the credit you are due, the difference will be included as part of your 2020 refund. If you have been overpaid by receiving the stimulus check, however, you will not be required to return any excess amount".
Under the CARES Act, if you are claimed, or qualify to be claimed, as a dependent on someone else’s 2019 (or 2018) return you cannot receive a stimulus check, in 2020. If you qualified as a dependent for 2019, but will not be for 2020, you will most likely get it in 2021, when you file a 2020 tax return.
If you have no income, you have to mail in a paper tax return. Some people advise that you report $1 of interest income, so that you can e-file.
