do
 _G.fs = {}
 local fT,hT = {},{["_c"]=0}
 function fs.mount(mp,pr)
  fT[mp] = pr
 end
 function fs.simplify(p)
  local pt,npt,rp = {},{},""
  for P in p:gmatch("[^/]+") do
   pt[#pt+1] = P
  end
  for k,v in pairs(pt) do
   if v == ".." then
    npt[#npt] = nil
   elseif v ~= "." then
    npt[#npt+1] = v
   end
  end
  for k,v in pairs(npt) do
   rp=rp.."/"..v
  end
  if p:sub(1,1) ~= "/" then rp = rp:sub(2) end
  return rp
 end
 function fs.resolve(p)
  if p:sub(1,1) ~= "/" then -- absolute/relative path
   p=(os.getenv("PWD") or "").."/"..p
  end
  p=fs.simplify(p)
  local pt,spt = {},""
  for P in p:gmatch("[^/]+") do
   pt[#pt+1] = P
  end
  for i = 2, #pt do
   spt=spt.."/"..pt[i]
  end
  return pt, pt[1], spt
 end
 function fs.exec(fc,m,...)
  return fT[fc][m](...)
 end
 function fs.open(p,m)
  local _,d,p = fs.resolve(p)
  local d = fT[d]
  local f,C=d.open(p,m),hT._c
  if f then
   hT._c = C + 1
   hT[C] = {d,f}
   return C
  end
  return false
 end
 function fs.close(h)
  if hT[h] then
   hT[h][1].close(hT[h][2])
  end
  return false
 end
 function fs.read(h,n)
  if hT[h] then
   return hT[h][1].read(hT[h][2],n)
  end
  return false
 end
 function fs.readall(f)
  local s=""
  repeat
   c=fs.read(f,2048)
   s=s..c
  until c==""
  return s
 end
 function fs.write(h,d)
  if hT[h] then
   return hT[h][1].write(hT[h][2],d)
  end
  return false
 end
 function fs.list(s)
  s=s or ""
  local _,d,p = fs.resolve(s)
  if not d then
   local kt = {}
   for k,v in pairs(fT) do
    kt[#kt+1] = k
   end
   return kt
  end
  return fT[d].list(p or "/")
 end
 function fs.mkdir(s)
  local _,d,p = fs.resolve(s)
  return fT[d].makeDirectory(p or "/")
 end
 function fs.rm(s)
  local _,d,p = fs.resolve(s)
  return fT[d].remove(p)
 end
 function fs.exists(s)
  local _,d,p = fs.resolve(s)
  return fT[d].exists(p)
 end
 function fs.isdir(s)
  local _,d,p = fs.resolve(s)
  return fT[d].isDirectory(p)
 end
end
function fs.cd(p)
 if p:sub(1,1) ~= "/" then
  p=(os.getenv("PWD") or "").."/"..p
 end
 p=fs.simplify(p)
 if fs.exists(p) and fs.isdir(p) then
  os.setenv("PWD",p)
 else
  error("non-existent/not a dir")
 end
end