Using grep -f when the file with patterns contains dots

Question

If I want to search for a string which contains a dot, in command line I can just prepend it with a backslash:

grep "string\." file.txt

or add -F -r parameters:

grep -F -r "string." file.txt

but there seems to be a problem if I want to use grep -f and have strings with dots inside the file with patterns.

I tried using quotes, prepending all the dots in the file with a backslash and using grep -F -r -f and even messed a bit with -E but none of these match the strings correctly without interpreting the dots as special characters.

How to achieve the desired behavior?

Answer 1

Insert a \\ before . :

grep -f  <(sed 's/\./\\./g' file_with_dots_inside.txt)  file.txt