fs_mt

function string.split(str,chars,num)
    num=tonumber(num)
    local tStrings={}
    local count=1
    local lastfound=1
    for at=1,str:len() do
        if str:sub(at,at+chars:len()-1)==chars then
            if num~=nil and count<num then
                count=count+1
            elseif num~=nil then
                return str:sub(1,at-1),str:sub(at+chars:len())
            else
                table.insert(tStrings,str:sub(lastfound,at-1))
                lastfound=at+chars:len()
            end
        end
    end
    if num==nil then
        table.insert(tStrings,str:sub(lastfound))
        return unpack(tStrings)
    end
    return false
end

function check(sDir)
    sDir=shell.resolve(sDir)
    local tPath={string.split(sDir,"/")}
    local at=""
    local i=1
    while i<=#tPath do
        local redirected=false
        local mtFile=fs.combine(at,"fsmetatable")
        at=fs.combine(at,tPath[i])
        if not fs.exists(at) and fs.exists(mtFile) then
            local mt=setmetatable({},{__index=getfenv()})
            setfenv(loadfile(mtFile),mt)()
            if mt.__index then
                at=check(type(mt.__index)=="function" and mt.__index(at,tPath[i]) or type(mt.__index)=="string" and fs.combine(mt.__index,tPath[i]))
                redirected=true
            end
        end
        if not redirected and not fs.exists(at) then
            error("'"..at.."' does not exist so '"..sDir.."' cannot exist",2)
        elseif not redirected and i<#tPath and not fs.isDir(at) then
            error("'"..at.."' is not a directory so '"..sDir.."' cannot exist",2)
        end
        i=i+1
    end
    return at
end