This LPIC-1 practice question tests your understanding of shells, scripting and data management. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which command combination will display a sorted list of unique lines from a file?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "which command"
Why it matters: Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
cat file | uniq | sort
Why wrong: uniq without prior sort removes only adjacent duplicates.
sort -u file
Why wrong: This works as well.
cat file | sort | uniq
Why wrong: This works but is not the only correct option.
Both A and C
Both methods yield sorted unique lines.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Both A and C
Option D is correct because both A and C produce a sorted list of unique lines from a file. In option A, `cat file | uniq | sort` first removes adjacent duplicates with `uniq`, then sorts the remaining lines, which yields a sorted unique list only if the file was already sorted. In option C, `cat file | sort | uniq` sorts the file first, then removes all duplicate lines (adjacent after sorting), guaranteeing a sorted unique list. Option B (`sort -u file`) also produces a sorted unique list, but it is not part of the combination asked for in the question.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
cat file | uniq | sort
Why it's wrong here
uniq without prior sort removes only adjacent duplicates.
sort -u file
Why it's wrong here
This works as well.
cat file | sort | uniq
Why it's wrong here
This works but is not the only correct option.
Both A and C
Why this is correct
Both methods yield sorted unique lines.
Clue confirmation
The clue word "which command" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates often assume `uniq` alone removes all duplicates, forgetting that it only works on adjacent lines, leading them to pick option A as correct without realizing the sorting order matters.
Detailed technical explanation
The `uniq` command only removes duplicate lines that are adjacent in the input stream, which is why sorting before `uniq` is essential to eliminate all duplicates. Under the hood, `sort -u` combines sorting and deduplication in a single pass, using an internal merge sort and a hash table to track seen lines, making it more efficient than piping `sort` to `uniq` for large files. In real-world log analysis, using `sort | uniq` is common when you need to preserve the original order of first occurrences (by using `sort -k` with a key), whereas `sort -u` is simpler for a fully sorted unique output.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
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FAQ
Shells, Scripting and Data Management — This question tests Shells, Scripting and Data Management — Read the scenario before looking for a memorised answer..
The correct answer is: Both A and C — Option D is correct because both A and C produce a sorted list of unique lines from a file. In option A, `cat file | uniq | sort` first removes adjacent duplicates with `uniq`, then sorts the remaining lines, which yields a sorted unique list only if the file was already sorted. In option C, `cat file | sort | uniq` sorts the file first, then removes all duplicate lines (adjacent after sorting), guaranteeing a sorted unique list. Option B (`sort -u file`) also produces a sorted unique list, but it is not part of the combination asked for in the question.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "which command". Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
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.
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