# This script triangulates each .obj file in the input directory
# using Blender's Python API (https://docs.blender.org/api/current/index.html)
# It assumes that that the input/ and output/ directories exist
# Run with `blender --background --python triangulate.py`
# Tested with Blender 2.81

# Note: Before running, make sure the default scene is empty by opening Blender, 
# selecting and deleting everything (light, camera, & cube), 
# and selecting File -> defaults -> Save startup file

import bpy
import glob

for f in glob.glob("input/*.obj"):
    basename = f.split('/')[1]
    bpy.ops.import_scene.obj(filepath=f)
    bpy.ops.export_scene.obj(filepath="output/{}".format(basename), use_triangles=True, use_materials=False)
    bpy.ops.object.delete()