The current command line rendering mechanism is direct rendering into a file. The driver is selected by setting the GRASS_RENDER_IMMEDIATE variable or by running d.mon module.
List of available display drivers:
Lets start with simple example of Python script called render.py:
#!/usr/bin/evn python
import os
import sys
import grass.script as grass
from grass.script import task as gtask
os.environ['GRASS_RENDER_IMMEDIATE'] = 'default'
os.environ['GRASS_RENDER_FILE'] = 'output.png'
cmd, dcmd = gtask.cmdstring_to_tuple(sys.argv[1])
grass.run_command('d.text', text="Test of GRASS_RENDER_COMMAND redirection")
os.environ['GRASS_RENDER_FILE_READ'] = 'TRUE'
grass.run_command(cmd, **dcmd)
export GRASS_RENDER_COMMAND=render.py
d.vect roadsmajor