replace all occurrences of a string in a text file linux command line code example

Example 1: linux replace string in all files

sed -i 's/old-text/new-text/g' input.txt

Example 2: Linux command line search and replace string in all files

String Find and replace (folders/sub folders)
> grep -rl "old string" . | xargs sed -i 's/old string/new string/g'

 URL Find and replace  (folders/sub folders) 
> grep -rl "www\.google\.com" . | xargs sed -i 's/www\.google\.com/www\.yahoo\.com/g'