Pure lua implementation of package.searchpath https://www.lua.org/manual/5.3/manual.html#pdf-package.searchpath

searchpath.lua

local DIRSEP = package.config:sub(1, 1)

local function is_readable(filename)
        local fd = io.open(filename, "r")
        if fd then
                fd:close()
                return true
        else
                return false
        end
end

function searchpath(name, path, sep, rep)
        assert(type(name) == "string")
        assert(type(path) == "string")
        if sep == nil then
                sep = "%."
        else
                assert(type(sep) == "string")
                sep = sep:gsub("[%%%^%$%(%)%.%[%]%*%+%-%?]", "%%%0") -- need to escape sep so it doesn't get interpreted as a pattern later
        end
        if rep == nil then
                rep = DIRSEP
        else
                assert(type(rep) == "string")
        end
        if #sep > 0 then
                name = name:gsub(sep, rep)
        end
        local msg = ""
        local repl_name = name:gsub("%%", "%%%%")
        for template in path:gmatch("[^;]+") do -- PATH_SEP
                local filename = template:gsub("%?", repl_name) -- PATH_MARK
                if is_readable(filename) then
                        return filename
                end
                msg = msg .. "\n\tno file '" .. filename .. "'"
        end
        return nil, msg
end