Doing a Search and Replace on the shell should not be difficult:

find . -name "*.html" -exec sed -i "s/searchPattern/replacePattern/g" {} +

However, on macOS this error message occurs:

sed: 1: "./aaa/a ...": invalid command code .
sed: 1: "./aaa/b ...": invalid command code .
sed: 1: "./aaa/c ...": invalid command code .
...

It turns out, on MacOS the -i parameter needs to be followed by an empty string:

find . -name "*.html" -exec sed -i "" "s/searchPattern/replacePattern/g" {} +