Structured scripting is the most suitable technique as it directly addresses all the core requirements in a foundational and efficient manner. This approach involves creating libraries of reusable functions that encapsulate the interactions with the S-U-T's Command Line Interface (CLI). This modularity directly leads to faster and cheaper maintenance (Requirement 1) and a lower cost for adding new tests (Requirement 2) because common operations are written once and reused. By centralizing the CLI commands within these functions, an abstraction layer is created, which provides a high level of independence from the specific tool or command syntax (Requirement 3). It provides the necessary benefits without the additional overhead of more complex frameworks.

A. Data-driven scripting: This technique focuses on separating test data from test logic, which is useful but does not inherently address the script's structural reusability, maintenance, or tool independence.

B. Keyword-driven scripting: While this offers a very high level of abstraction, it requires a more complex framework (e.g., a keyword interpreter). For a CLI, a well-structured function library often provides sufficient clarity and abstraction, making the additional complexity of a keyword-driven framework potentially unnecessary.

C. Linear scripting: This record-and-playback style results in scripts that are difficult to maintain and have little to no reusability, directly contradicting the stated requirements.

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1. ISTQB® Certified Tester Advanced Level Test Automation Engineer Syllabus Version 3.1.1 (2019).

Section 4.1.2, Scripting Techniques, page 21: Describes "Structured Scripting" as a technique that "makes use of a library of reusable functions" and notes its advantages in "maintainability and reusability of test scripts." This directly supports the choice of structured scripting for meeting requirements of low-cost maintenance and addition of new tests.

2. Black, R. (2015). Advanced Software Testing - Vol. 3, 2nd Edition: Guide to the ISTQB Advanced Certification as an Advanced Test Automation Engineer. Rocky Nook.

Chapter 4, Section 4.2.2, "Approaches to Automating Test Cases", pages 106-107: This section explains that structured scripting involves creating a library of shared procedures that can be called by test scripts. It explicitly states, "This approach can substantially reduce the cost of test script maintenance." This aligns with the requirements for cost-effective maintenance and extensibility. It is presented as a fundamental improvement over linear scripting and a basis for more abstract approaches.