## Function: COMMON-LISP:OPEN
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> Return a stream which reads from or writes to FILENAME.
> Defined keywords:
> :DIRECTION - one of :INPUT, :OUTPUT, :IO, or :PROBE
> :ELEMENT-TYPE - the type of object to read or write, default BASE-CHAR
> :IF-EXISTS - one of :ERROR, :NEW-VERSION, :RENAME, :RENAME-AND-DELETE,
> :OVERWRITE, :APPEND, :SUPERSEDE or NIL
> :IF-DOES-NOT-EXIST - one of :ERROR, :CREATE or NIL
> See the manual for details.

### Lambda list
```cl
(sb-kernel:filename &key sb-impl::direction sb-impl::element-type sb-impl::if-exists
 sb-impl::if-does-not-exist sb-impl::external-format class)
```