base = "c:/windows/"
path = "./data/text.txt"
pt = Pathname.new(base) + path
puts pt, pt.cleanpath

base = "c:\\windows\\"
path = ".\\data\\text.txt"
pt = Pathname.new(base) + path
puts pt, pt.cleanpath

なんじゃこりゃー
c:/windows/./data/text.txt
c:/windows/data/text.txt
c:\windows\/.\data\text.txt
c:\windows\/.\data\text.txt