sed edit file in place

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

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.

Note that on OS X you might get strange errors like "invalid command code" or other strange errors when running this command. To fix this issue try

sed -i '' -e "s/STRING_TO_REPLACE/STRING_TO_REPLACE_IT/g" <file>

This is because on the OSX version of sed, the -i option expects an extension argument so your command is actually parsed as the extension argument and the file path is interpreted as the command code. Source: https://stackoverflow.com/a/19457213