Final answer:
The keyboard shortcut Ctrl + C is used to terminate a search in progress or interrupt a command in command-line interfaces.
Step-by-step explanation:
The keyboard shortcut to terminate a search in progress or to interrupt a command in many command-line interfaces is b. Ctrl + C. This command sends a SIGINT signal, telling the program to abort the current task. For example, if you are searching through large files using a command-line search tool and want to stop the process, you can press Ctrl + C to end it immediately.