CompTIA Linux+ XK0-006 (V8) Practice Question

The single-bracket test command (the [ builtin) is specified by POSIX and is available in every /bin/sh implementation. Using the numeric operator -le performs an integer "less than or equal" comparison. Double-quoting the variable suppresses word splitting and pathname expansion and ensures that an empty value is passed as a blank string instead of disappearing, which would make the operator lose its left-hand operand and raise the "unary operator expected" error. The other choices all have drawbacks:

• [[ $COUNT -le 50 ]] relies on the Bash-specific double-bracket construct and is not guaranteed to exist in a rescue /bin/sh.
• (( COUNT <= 50 )) uses arithmetic evaluation that many POSIX shells (for example dash or the original Bourne shell) do not implement.
• [ $COUNT -le 50 ] omits the protective quotes; if COUNT is empty or contains spaces, the test receives the wrong number of arguments and can fail with the same unary-operator error the question seeks to avoid. Therefore, quoting the variable inside the portable single-bracket test is the only safe and universally compatible solution.