Bought a cactus and it has no roots...not sure if it's rotting?

[elizabethAZ]

I just bought a cactus from a hardware store and brought it home to repot it, but when I took it out of the pot, I found that it had no roots. I'm not sure if it's rotting at all - there are some brown patches on the bottom. Is this rot, or is it okay (see pics)? If it is rotting, do I need to cut the bottom off? If it's not rotting, should i repot it in soil now with no roots? Or should I leave it out and wait for roots to grow before putting it in a pot with soil? Any help appreciated! Thanks!

[ElieEstephane]

Touch the black spots and see if they are mushy or firm. It looks a little damp to me. If you have some, give the bottom a few sprays of hydrogen peroxide. Let the cactus dry a few days and repot it in a cactus mix with extra grit added but hold off water until spring.

[elizabethAZ]

The black spots are firm, so that means it's not rotting? I'll spray with hydrogen peroxide and repot in a few days. Thank you!

[ElieEstephane]

If it's firm then no rot. Rot is very squishy and you'd know it. Let it dry well for a few days and check it again. You can even leave it unpotted in the shade until spring comes.
Btw it's probably a cereus peruvianus

[elizabethAZ]

Sounds good, thank you so much! And I think you're right about it being a cereus peruvianus! I had no idea what it was before...thanks!!