>i am using something like this
>select a
>use filename
>set index to
>commands
>(but right here i want to close it)

OK, but you still shouldn't do the SELECT a.

Try it this way:

SELECT 0          && SELECTS next available workarea
USE filename      && This will give a default alias of "filename"
SET INDEX TO ...
commands...
USE IN filename   && this will close your file no matter what the current workarea is