XK0-006 Automation, Orchestration, and Scripting Practice Question
In a Bash script, the administrator wants to capture the output of a command into a variable. Which syntax should be used?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
$(command)
Command substitution can be done with $(command) or backticks `command`. The latter is deprecated. $(( )) is for arithmetic expansion. $VAR is for variable expansion.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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$VAR
Why it's wrong here
$VAR expands an existing variable's value; it does not execute a command or capture its output. It is tempting because variable expansion is the everyday way to read stored values, and would be correct where the value already exists and simply needs to be referenced elsewhere in the script.
- ✗
$((command))
Why it's wrong here
$((...)) performs arithmetic expansion, evaluating integer expressions, so it cannot capture command output. It is tempting because the syntax resembles command substitution and is used constantly in scripts, and would be correct where the administrator needs to compute a numeric value from variables.
- ✗
`command`
Why it's wrong here
Backticks alone execute the command and substitute its output into the surrounding command line; they do not assign anything to a variable. The tempting use is inline substitution within another command, such as echo "Today is `date`", which is correct when no variable storage is needed.
- ✓
$(command)
Why this is correct
Command substitution with $(command) runs the command in a subshell and substitutes its standard output, which is then assigned to the variable. Backticks achieve the same but nest poorly; $(...) is the modern, preferred syntax.
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Related to this question
Key term
Bash script
A Bash script is a text file containing a sequence of commands for the Unix shell Bash, allowing users to automate repetitive tasks and streamline system administration on Linux and macOS.
Key term
Output
In IT service management, output is the result or deliverable produced by a process, system, or component, such as data, reports, or services delivered to a customer.
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Written by Johnson Ajibi, MSc IT Security
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