Find the files existing in one directory but not in the other [closed]

I’m trying to find the files existing in one directory but not in the other, I tried to use this command:

diff -q dir1 dir2

The problem with the above command that it finds both the files in dir1 but not in dir2 as well as the files in dir2 but not in dir1,

I am trying to find the files in dir1 but not in dir2 only.

Here’s a small sample of what my data looks like

dir1    dir2    dir3
1.txt   1.txt   1.txt
2.txt   3.txt   3.txt
5.txt   4.txt   5.txt
6.txt   7.txt   8.txt

Another question on my mind is how can I find the files in dir1 but not in dir2 or dir3 in a single command?