Pre-render create directory

Custom parameter (shader_node) with path to node with filename parameter (if You use it in shader etc.):

`opfullpath("/obj/geo_heating/shopnet/material_bake/heating_pc_v001")`

Pre-render script to create non-existent directory:

import os
path = hou.pwd().parm('shader_node').evalAsString()
dirName = os.path.dirname(hou.node(path).parm('filename').evalAsString())
if not os.path.exists(dirName):
    os.makedirs(dirName)