How to Save sed Output Directly to a File
You have 3 options here:
Option 1: use tee with sed
sed 's/Hello/Hi/g' file-name | tee file
Option 2: use > with sed
sed 's/Hello/Hi/g' file-name > file
Option 3: use sed with -i option
sed -i 's/Hello/Hi/g' file-name