After modifying multiple files, how can I save all their buffers?
After making the changes you can save the open buffers using
save-some-buffers. This is bound
C-x s by default.
Here is what the docs say.
Save some modified file-visiting buffers. Asks user about each one. You can answer `y' to save, `n' not to save, `C-r' to look at the buffer in question with `view-buffer' before deciding or `d' to view the differences using `diff-buffer-with-file'.
You can use
C-u C-x s to save without asking.