This LFCS practice question tests your understanding of essential commands. 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.
A script needs to search for lines containing 'ERROR' in /var/log/syslog and count them. Which command pipeline achieves this?
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.
Why wrong: Also counts matching lines, though without pipeline; but it's correct technically, but the question asks for pipeline. However, this is also valid; but we need to choose best. Actually, this is also correct but the question says 'pipeline', so B is the answer.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
grep ERROR /var/log/syslog | wc -l
Option C is correct because it uses `grep` to filter lines containing 'ERROR' from `/var/log/syslog` and pipes the output to `wc -l`, which counts the number of lines. This pipeline accurately counts the lines that match the pattern, which is the required task.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
wc -l /var/log/syslog
Why it's wrong here
Counts total lines in the file.
✗
grep ERROR /var/log/syslog | wc -c
Why it's wrong here
Counts characters, not lines.
✓
grep ERROR /var/log/syslog | wc -l
Why this is correct
Filters ERROR lines and counts them.
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.
✗
grep -c ERROR /var/log/syslog
Why it's wrong here
Also counts matching lines, though without pipeline; but it's correct technically, but the question asks for pipeline. However, this is also valid; but we need to choose best. Actually, this is also correct but the question says 'pipeline', so B is the answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may choose `grep -c` (option D) because it achieves the same result, but the question specifically requires a pipeline, and Linux Foundation often tests the literal interpretation of 'command pipeline' to catch those who overlook the wording.
Detailed technical explanation
How to think about this question
The `grep -c` option is a more efficient way to count matches without piping to `wc -l`, as it avoids spawning an extra process. However, the LFCS exam often tests understanding of command pipelines and the distinction between `wc -l` (line count) and `wc -c` (byte count). In real-world log analysis, using `grep -c` is preferred for performance, but the question's wording 'command pipeline' makes `grep | wc -l` the expected answer.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
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
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Essential Commands — This question tests Essential Commands — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: grep ERROR /var/log/syslog | wc -l — Option C is correct because it uses `grep` to filter lines containing 'ERROR' from `/var/log/syslog` and pipes the output to `wc -l`, which counts the number of lines. This pipeline accurately counts the lines that match the pattern, which is the required task.
What should I do if I get this LFCS question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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