sed edit file in place
Solution 1:
The -i option streams the edited content into a new file and then renames it behind the scenes, anyway.
Example:
sed -i 's/STRING_TO_REPLACE/STRING_TO_REPLACE_IT/g' filename
while on macOS you need:
sed -i '' 's/STRING_TO_REPLACE/STRING_TO_REPLACE_IT/g' filename
Solution 2:
On a system where sed does not have the ability to edit files in place, I think the better solution would be to use perl:
perl -pi -e 's/foo/bar/g' file.txt
Although this does create a temporary file, it replaces the original because an empty in place suffix/extension has been supplied.