How to find and replace all occurrences of a string recursively in a directory tree? [duplicate]

Try this:

find /home/user/ -type f | xargs sed -i  's/a\.example\.com/b.example.com/g'

In case you want to ignore dot directories

find . \( ! -regex '.*/\..*' \) -type f | xargs sed -i 's/a\.example\.com/b.example.com/g'

Edit: escaped dots in search expression