Determine If Any File Changed In Directory For Latest Git Commit

You can get the added, modified, deleted and renamed files in the latest commit with:

git diff --name-only --diff-filter=AMDR --cached @~..@

To get the changes affecting a specific directory, filter the output using grep. For example:

changes() {
  git diff --name-only --diff-filter=AMDR --cached @~..@
}

if changes | grep -q dirname {
  echo "start expensive operation"
}