bash - Diffrence between two directories -

below question: suppose in dira have these files:

file1 file2 file3 file4

and in dirb have below files:

file1 file2 file3

now if have make script tells me diffrence between 2 directorie (in case file4 missing in dirb) , copies file in dirb, commands?

this show brief summary of differences:

diff -rq dir1 dir2

it tell if file exists in 1 of directories, or if file exists in both directories different content tell different. in example go like:

$ diff -rq dir1 dir2 in dir1: file4

if want see more details, drop -q flag (it stands "quiet").

And