How to save file in Nano fast

Edit the file ~/.nanorc and add this:

bind ^S savefile main

Now ctrl+s will save your file to the same filename without prompts.

However, use this feature with caution. It will not inform you if something else has modified the file since your last save. If that's not a possible issue for you, this should work good!

Since at least Nano v3, the native Ctrl+S shortcut will directly save the file. Ctrl+O is the "Save As…" feature.