git diff from commit code example

Example 1: git diff two commits

-> git diff 0da94be  59ff30c > my.patch
-> git apply my.patch

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