XK0-006 System Management Practice Question
An administrator wants to replace all occurrences of 'oldstring' with 'newstring' in a configuration file named config.cfg, and save the changes. Which sed command should be used?
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
✓
sed -i 's/oldstring/newstring/g' config.cfg
It uses -i for in-place editing and g to replace all occurrences on each line. Option A has -i but lacks g, so it replaces only the first occurrence per line. Option C adds an unnecessary i flag for case-insensitive matching, which deviates from the requirement to replace 'oldstring' exactly as given. Option D lacks -i, so changes are only printed to stdout and not saved.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
sed -i 's/oldstring/newstring/' config.cfg
Why it's wrong here
Missing g flag, only replaces first occurrence per line.
- ✓
sed -i 's/oldstring/newstring/g' config.cfg
Why this is correct
Correct: in-place global substitution.
- ✗
sed -i 's/oldstring/newstring/gi' config.cfg
Why it's wrong here
i flag after s is not valid; i for case-insensitive would be /I or /i in some versions, but traditional sed uses /g only.
- ✗
sed 's/oldstring/newstring/' config.cfg
Why it's wrong here
No -i for in-place, no g for global.
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