I was sexually assaulted by man he rubbed my anus with his penis covered by his underwear and also my underwaer on i'm scared can i catch hiv or any std by this way ?

You get STD's when there is a transfer of sexual fluids from an infected person to the recipient. HIV requires bloody fluid transfer to a site where there is tissue. If there was no fluid transfer your risk is minimal. Get tested if you wish.

HIV is transmitted through broken skin, open wounds, but mostly through mucosal membranes which is not what above scenario describes, fabric acts as protection. A reliable site is cdc.gov in clarifying STD’s in general.

You are not at risk of STDs from what you described, However, you should consult a mental health professional for counselling to address the trauma to your mind. Wish you good health!