@wrefgtzweve I'm not a fan of this being the solution to the problem, because if I remember correctly advdupe2 used to have this restriction, but removed it. Why reintroduce the restriction again instead of addressing the actual problem with periods and spacing?

It seems like just in general, the function doesnt like leading/trailing spaces after a dot. You could use a gsub to handle that; "%s*%.%s*" and gsub with "." would be enough

local tests = {
    "test. test.txt",
    "test .test.txt",
    "test . test.txt",
    "test   . test.txt",
    "test .       .       .        test.txt",
}

for _, test in ipairs(tests) do
    local fixed = test:gsub("%s*%.%s*", "."):gsub("%.%.+", ".")
    print(test, "->", fixed, " - file.Write result ", file.Write(fixed, "nothing"))
end

Adding the second gsub would handle multiple periods too which file.Write also doesn't like

@wrefgtzweve I'm not a fan of this being the solution to the problem, because if I remember correctly advdupe2 used to have this restriction, but removed it. Why reintroduce the restriction again instead of addressing the actual problem with periods and spacing?

It seems like just in general, the function doesnt like leading/trailing spaces after a dot. You could use a gsub to handle that; "%s*%.%s*" and gsub with "." would be enough

Yeah i agree, i've improved it