Prolog - How to make a variable list out of a given list from input file?

Question

I have a input predicate will read the file as a list: input(Filename,List). The list then will be in the format of

[\"_\",\"_\",\"_\",9,\"_\",\"_\"]

Answer 1

to_var_list([],[]).
to_var_list([A|R1],[B|R2]):-
     (A = '_' ->
      true;
      A = B),
    to_var_list(R1,R2).

Exchange '_' with "_" if you actually have one character strings and not underscore atoms. Also, there is a read predicate that does something like you want to achieve, but it expects a . after your lists in the file.