Define or declare a URL loader object according to the specific requirements of your programming language.
Declare a URL request object that points to the text file containing the URL variables with which you want to populate the text fields.
Declare the format property of the URL loader object so the URL loader will interpret the URL variables in the text file as URL-encoded name/value pairs.
Use a load file method to move the contents of the URL variable text file into the URL loader object. Add any code necessary to detect that the contents of the URL variable text file have been successfully transferred to the URL loader object, and to report whether the process was successful.
Store the contents of the specific URL variable (as identified in the URL variable text file with a unique variable name) in the text field that you want to populate with the URL variable. Equate the text field variable to the URL loader object with the data property and URL variable's name attached in order to populate a specific text field with a specific URL variable value.