CompTIA Server+ SK0-005 Practice Question

In Bash an until loop executes its body repeatedly while the test command returns a non-zero (false) exit status, and it stops as soon as that command succeeds (exit status 0). Because nc -z localhost 443 fails until the port is open, wrapping the command in an until loop makes the script wait and then continue automatically when the service is ready.

A while loop has the opposite logic (it repeats only while the test command succeeds), so it would loop after the port is already open and exit immediately when the port is closed. A for loop requires a predefined list or counter and would need extra logic to stop at the right time, while a case statement is used for single evaluations rather than continuous polling. Therefore, the until loop is the most appropriate construct.