In config.txt some lines contain the word `foo` more than once. Which command prints the file with EVERY occurrence on every line replaced by `bar`, leaving the file itself unchanged?
LPIC-1 Exam 101-500, objective 103. GNU and Unix commands medium
Machine-checked — no person has signed for it. This question was read against the source cited below by an automated pass, which found no contradiction. That is a weaker claim than it sounds: the same kind of process wrote the question, so it can confirm its own mistake.
Treat it as a good draft rather than as settled fact, and read the source below before you rely on it. It is not used in mock exams here — only questions a person has signed for are.
How these questions are written — where each question comes from, what the verification ledger records, and what happens when one is found wrong.
The options
Not correct sed 's/foo/bar/' config.txt
Wrong. Without a flag, sed substitutes only the FIRST match on each line; later occurrences on the same line survive.
Correct sed 's/foo/bar/g' config.txt
Correct. The trailing g flag makes the substitution global within each line, and sed writes the result to standard output without touching the file.
Not correct sed -n 's/foo/bar/g' config.txt
Wrong. -n suppresses the automatic printing of each line, and there is no p flag here, so this command produces no output at all.
Not correct sed -i 's/foo/bar/g' config.txt
Wrong for this question, though the substitution itself is right. -i edits the file in place, which the question explicitly forbids, and it prints nothing.
Why
sed's substitute command is s/pattern/replacement/flags. Useful flags: g for every match on the line, a number for the nth match, p to print (paired with -n to print only matching lines), i for case-insensitive matching. The -i OPTION (not the flag) rewrites the file in place and is the one to be careful with.
Where this comes from
- Cited
- LPI exam objective 103.2
- What it says
- Use sed to perform substitutions on a text stream.
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 103 and space the ones you get wrong.
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