given two directory trees how to find which files are the same?

Question

I am writing a bash script, and I would like to know which files are the same in two directory trees.

It would be the opposite of using diff.

Well i found the a

Answer 1

Well i found the answer myself. I had tried it before, but I thought it did not work.

diff -srq dir1/ dir2/ | grep identical

What -srq means? From diff --help :

-s  --report-identical-files  Report when two files are the same.
-r  --recursive  Recursively compare any subdirectories found.
-q  --brief  Output only whether files differ.