His all.
In unity, there’s a script for importing .blend
I guess that it works with unity launching blender with the blend file as parameter and running a small script that ask blender to export fbx file.
Of course all this can be done by hand but beeing automated is pretty appreciable.
here’s this small piece of code:
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import bpy.ops
import bpy
minor = bpy.app.version[1]
blender280 = minor >= 80
if not blender280:
try:
import io_scene_fbx.export_fbx
except:
print('error: io_scene_fbx.export_fbx not found.')
# This might need to be bpy.Quit()
raise
# Find the Blender output file
import os
outfile = os.getenv("UNITY_BLENDER_EXPORTER_OUTPUT_FILE")
# Do the conversion
print("Starting blender to FBX conversion " + outfile)
if blender280:
bpy.ops.export_scene.fbx(filepath=outfile,
check_existing=False,
use_selection=False,
use_active_collection=False,
object_types= {'ARMATURE','CAMERA','LIGHT','MESH','EMPTY'},
use_mesh_modifiers=True,
mesh_smooth_type='OFF',
use_custom_props=True,
apply_scale_options='FBX_SCALE_ALL'
)
else:
# blender 2.58 or newer
import math
from mathutils import Matrix
# -90 degrees
mtx4_x90n = Matrix.Rotation(-math.pi / 2.0, 4, 'X')
print("moo")
class FakeOp:
def report(self, tp, msg):
print("%s: %s" % (tp, msg))
exportObjects = ['ARMATURE', 'EMPTY', 'MESH']
minorVersion = bpy.app.version[1];
if minorVersion <= 58:
# 2.58
io_scene_fbx.export_fbx.save(FakeOp(), bpy.context, filepath=outfile,
global_matrix=mtx4_x90n,
use_selection=False,
object_types=exportObjects,
mesh_apply_modifiers=True,
ANIM_ENABLE=True,
ANIM_OPTIMIZE=False,
ANIM_OPTIMIZE_PRECISSION=6,
ANIM_ACTION_ALL=True,
batch_mode='OFF',
BATCH_OWN_DIR=False)
else:
# 2.59 and later
kwargs = io_scene_fbx.export_fbx.defaults_unity3d()
io_scene_fbx.export_fbx.save(FakeOp(), bpy.context, filepath=outfile, **kwargs)
# HQ normals are not supported in the current exporter
print("Finished blender to FBX conversion " + outfile)
I tried to modify this code but without any success 
I changed the end of this script with this:
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# 2.59 and later
# HACK SELECTIVE BLENDER IMPORT
for obj in bpy.data.objects:
obj.select = False if obj.name[0] in '_.' else True
#end HACK
kwargs = io_scene_fbx.export_fbx.defaults_unity3d()
# HACK SELECTIVE BLENDER IMPORT
kwargs["use_selection"] = True
#end HACK
io_scene_fbx.export_fbx.save(FakeOp(), bpy.context, filepath=outfile, **kwargs)
# HQ normals are not supported in the current exporter
print("Finished blender to FBX conversion " + outfile)
What i would like to achieve is to prevent blender from exporting objects with a name starting with an ‘_’
Sounds pretty simple to achieve but i could not make this work
could anyone help me please and tell me what am doing wrong ?
thanks in advance 
and happy blending !