Find all regular files under current directory (excluding hidden directories) and replace every occurrences of 'subdomainA.example.com' with 'subdomainB.example.com' in those files
find . \( ! -regex '.*/\..*' \) -type f -print0 | xargs -0 sed -i 's/subdomainA.example.com/subdomainB.example.com/g'