ruby随机生成字符串

随机生成一个固定位数的字符串：

def newpass( len )
    chars = ("a".."z").to_a + ("A".."Z").to_a + ("0".."9").to_a
    newpass = ""
    1.upto(len) { |i| newpass << chars[rand(chars.size-1)] }
    return newpass
end
puts   newpass(15)