
e1 = 1.0 ;
lc = e1/4 ;

Point (1) = { 0.0, 0.0, 0.0, lc };
Point (2) = {  e1, 0.0, 0.0, lc };
Point (3) = {  e1,  e1, 0.0, lc };
Point (4) = { 0.0,  e1, 0.0, lc };

Line   (1) = { 1, 2 };
Line   (2) = { 2, 3 };
Line   (3) = { 3, 4 };
Line   (4) = { 4, 1 } ;

Line Loop (10) = { 1, 2, 3, 4 }; 
Plane Surface (11) = { 10 };

Extrude Surface { 11, {  0.0, 0.0, e1 }  } ; 

// the command $ gmsh -0 forum_gmsh.geo 
// give me a lot of usefull informations about the 5 new surfaces :
// Line Loop (1000020) = {1, 19, -13, -18};
// Ruled Surface (20) = {1000020};
// Line Loop (1000024) = {2, 23, -14, -19};
// Ruled Surface (24) = {1000024};
// Line Loop (1000028) = {3, 27, -15, -23};
// Ruled Surface (28) = {1000028};
// Line Loop (1000032) = {4, 18, -16, -27};
// Ruled Surface (32) = {1000032};
// Line Loop (1000033) = {13, 14, 15, 16};
// Plane Surface (33) = {1000033};

// Is there a way to get this surface numbers inside the gmsh command file ?
// It could be usefull for defining physical entities for applying loads and/or limit conditions.

// of course I have tried 
// newsurfs[] = Extrude Surface { 11, {  0.0, 0.0, e1 }  } ; 
// but it results in parse error :)
