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Shells, Scripting and Data Management →mediumMultiple ChoiceObjective-mapped

LPIC-1 Shells, Scripting and Data Management Practice Question

A shell script uses the variable expansion ${var:-default} to set a default value for an environment variable. The script prints unexpected output when the variable is set to an empty string. Which expansion should be used to ensure the default is only used when the variable is unset, not when it is empty?

⚠ Common exam trap

Test-takers frequently confuse the colon modifier, assuming `${var:-default}` and `${var-default}` behave identically, when in fact the colon adds the empty-string check that causes the unexpected behavior described in the question.

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

✓

${var-default}

The expansion `${var-default}` uses the default value only when the variable is unset (i.e., does not exist at all). In contrast, `${var:-default}` also substitutes the default when the variable is set but empty, which causes the unexpected output described in the question. The colon in the expansion is the critical difference: it adds the check for a null or empty string.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • ✗

    ${var:-default}

    Why it's wrong here

    Also applies when var is empty.

  • ✓

    ${var-default}

    Why this is correct

    Only applies when var is unset.

  • ✗

    ${var:?default}

    Why it's wrong here

    Prints error if unset or empty.

  • ✗

    ${var:=default}

    Why it's wrong here

    Also assigns the default to var.

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JA

Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

This LPIC-1 practice question is part of Courseiva's free LPI certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the LPIC-1 exam.