A trivial implementation would be to open the file, check if the numbers exist till the 6th line and display which file is being read.
file = fopen('sample.txt');
line = fgetl(file);
for i=1:6
if any(line >= '0' & line <= '9')
disp("The fifth line contains numbers => first file")
else
disp("The fifth line does not contain numbers => second file")
line = fgetl(file);
end
fclose(file);
