import bpy
import os

filename = 'blender_script.run'

def scan_for_file_to_exec(scn):

    global filename

    try:
        file = open(filename)

    except FileNotFoundError:
        pass
    else:
        print("scan_for_file_to_exec: Got file")
        content = file.read()
        file.close()
        os.remove(filename)
        exec(content)

bpy.app.handlers.scene_update_pre.append(scan_for_file_to_exec)

print("scan_for_file_to_exec: Scanning for file '%s' in directory '%s'" % (filename, os.getcwd()))