[Gmsh] 3D volume as tetrahedra only

[Bartek Grychtol]

Hi,

I'm new to gmsh, just seeing if it can do what I need.
I have a surface mesh in an stl file. I need to create a nice 
tetrahedral volume mesh,
but without changing anything on the surface.
The sphere demo does exactly that.
However, the generated .msh file contains both triangles (for the 
surface) and
tetrahedra (for the volume inside).
Is there a way (a command or file format) to have the complete mesh 
represented as tetrahedra only?

Best wishes,

Bartek