LPIC-1 Shells, Scripting and Data Management Practice Question
Which sed command will replace the first occurrence of 'foo' with 'bar' on each line of a file?
⚠ Common exam trap
It's easy for candidates to 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.
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 's/foo/bar/' file
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.
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 '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.
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