<｜begin▁of▁sentence｜>### Instruction:
Given a template string containing $-substitutions like 'Your terminal size is $COLUMNS x $ROWS.', how can you use the 'render' method of the 'TerminalController' class to replace each substitution with the corresponding terminal control string or '' if it's not defined?
### Response:
import json

# Assuming TerminalController is a class we have access to,
# and render is a method that performs the described substitution.
class TerminalController:
    def render(self, template_str):
        # This function would contain the logic to replace $-substitutions
        pass

# Create an instance of the TerminalController class
term_controller = TerminalController()

# Template string with $-substitutions
template = 'Your terminal size is $COLUMNS x $ROWS.'

# Using the render method of our TerminalController to process the string
rendered_string = term_controller.render(template)

# Output the result
print(rendered_string)
<|EOT|>
