# bash examples:
1='original_string'2='new______string'
# for this (the original-poster's) question:1='subdomainA.example.com'2='subdomainB.example.com'
# 'fdfind' (on at least Ubuntu 20.04) = 'fd' = https://github.com/sharkdp/fd
fdfind . --type f --exec sed -i "s/$1/$2/g"
# Here's a slightly-more-complex example that# a. excludes (-E) .git/ and archive/ dirs, and# b. performs a word-boundary search on the original_string (\<$1\>):fdfind . -E .git/ -E archive/ --type f --exec sed -i "s/\<$1\>/$2/g"