sorry  it seems i put my comment in the wrong place  if a user explicitly chooses to download into then we are not here to prevent stupidity  so i am not too concerned about the setting of output dir  the real issue i was trying to address in my comment is related to  out no prefix if i have an object path like  container object path opt swift there is no warning or path checking to stop me setting out no prefix to  container object path  and trying to write files out into  opt  i think there is a good case for stripping leading s from the path after line before we deal with out directory  that should give users the flexibility they need whilst removing a potential source of errors  what do you think 