idlwave-auto-write-paths

idlwave-auto-write-paths is a variable defined in `idlwave.el'.
Its value is

t

Documentation:
Write out path (!PATH) and system directory (!DIR) info automatically.
Path info is needed to locate library catalog files. If non-nil,
whenever the path-list changes as a result of shell-query, etc., it is
written to file. Otherwise, the menu option "Write Paths" can be
used to force a write.

You can customize this variable.