check in git diff code example
Example 1: git diff of a file between two commits
git diff <branch_hash> <other_branch_hash> -- <file_path>
Example 2: make diff git as commit
A simple way to do it is:
create and checkout branch tmp at branch_a (git branch tmp branch_a && git checkout tmp)
git reset --soft branch_b
git commit
that commit must have all the diff