Search recursively all files with a given name replacing a word

Question

From a given folder, I want to search recursively accross all subfolders searching for files with name file.txt replacing all occurences of Foo -case sensitive- with Bar.

Which is the simplest way of achieving this with basic scripting (Bash / sed / grep / find...).

Answer 1

find + sed solution:

find . -type f -name "file.txt" -exec sed -i 's/Foo/Bar/g' {} \;