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 sed command will replace the first occurrence of 'foo' with 'bar' on each line of a file?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
sed 's/foo/bar/g' file
Why wrong: The g flag replaces all occurrences.
sed 's/foo/bar/0' file
Why wrong: Invalid flag 0; sed would error.
sed 's/foo/bar/2' file
Why wrong: Replaces the second occurrence per line.
sed 's/foo/bar/' file
Default replaces first occurrence per line.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
sed 's/foo/bar/' file
Option D is correct because the default behavior of the `s` (substitute) command in sed is to replace only the first occurrence of the pattern on each line. Without a numeric flag, `sed 's/foo/bar/' file` replaces the first 'foo' on each line with 'bar'. The `g` flag would replace all occurrences, not just the first.
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.
sed 's/foo/bar/g' file
Why it's wrong here
The g flag replaces all occurrences.
sed 's/foo/bar/0' file
Why it's wrong here
Invalid flag 0; sed would error.
sed 's/foo/bar/2' file
Why it's wrong here
Replaces the second occurrence per line.
sed 's/foo/bar/' file
Why this is correct
Default replaces first occurrence per line.
Clue confirmation
The clue word "first" 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 confuse the default behavior of sed's substitute command, assuming it replaces all occurrences unless told otherwise, and thus incorrectly choose the `g` flag option.
Detailed technical explanation
The sed substitute command `s/pattern/replacement/flags` uses an optional numeric flag to specify which occurrence to replace; if omitted, it defaults to the first. The `g` flag is a separate flag that applies the substitution globally. Under the hood, sed processes each line sequentially, applying the substitution to the first match unless a different occurrence number is given. In real-world scripting, this distinction is crucial when you need to modify only the first instance of a pattern, such as changing the first IP address in a configuration file while leaving others intact.
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: sed 's/foo/bar/' file — Option D is correct because the default behavior of the `s` (substitute) command in sed is to replace only the first occurrence of the pattern on each line. Without a numeric flag, `sed 's/foo/bar/' file` replaces the first 'foo' on each line with 'bar'. The `g` flag would replace all occurrences, not just the first.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
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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