This is a nice little command to search and replace one type of content with another. It recursively parses through directories and files.
Be very careful when running this command, because it can do a lot of damage
Below is an example of replacing all "http" with "https" inside a directory /var/www:
find /var/www/ -type f -print0 | xargs -0 sed -i 's/http:/https:/g'
The variables that you should change:
What to change: http
What to change to: https
The replacement is done using sed and it matches regular expressions. So you should escape your variables (eg: www.example.com should be www.example.com inside the s/http:/https:/g)