The UDP (User Defined Program) system is a scripting framework for controlling and extending instrumentation software. It has been specially designed for air- and space-borne instruments with flexibility, error control, reuse, automation, traceability and ease of development as its main objectives. All the system applications are connected through a database containing the valid script commands including descriptive information and source code. The system can be adapted to different projects without changes in the framework tools, thus achieving great level of flexibility and reusability. The UDP system comprises: an embedded system for the execution of scripts by the instrument software; automatic tools for aiding in the creation, modification, documentation and tracing of new scripting language commands; and interfaces for the creation of scripts and execution control.