Unix is simple and straight. It’s not ask you when you tell it to do something. For example, if you ask to move a file to the directory with same-named file… Unix will replace it without any words.
But we can ask Unix do it more “carefully”.
Merge one folder to another, but don’t override any existing files:
mv -n ./dir1/* ./dir2/
Take backup of destination file before overwriting existing file:
mv -bv ./dir1/* ./dir2/
-b is for backup,
-v is for verbose mode.