Find & Replace: sed

The sed command (stream editor) performs text transformations on the fly. Its most common use is find and replace:

sed 's/old/new/' file.txt

The s stands for substitute. This replaces the first occurrence of old with new on each line.

Replace all occurrences on each line with g

sed 's/error/WARNING/g' log.txt

The trailing g (global) replaces every match on the line, not just the first.

sed does not modify the original file

By default, sed prints the result to stdout. The file stays unchanged. To save, use redirection:

sed 's/old/new/g' data.txt > data_fixed.txt

Delimiters

The / is conventional but you can use any character:

sed 's|/usr/bin|/opt/bin|g' paths.txt

Using | avoids escaping all those slashes.

Mission: Inspection Report Fix

The station just passed its safety re-inspection, but report.txt still shows old FAIL results from the previous round. The captain wants a clean report on file before the delegation arrives.

1. Use sed to replace all occurrences of FAIL with PASS in report.txt and display the corrected report.
2. Save the corrected report into a new file called report-clean.txt.
3. Create a folder called records and move report-clean.txt into it.
4. Count how many tests now show PASS.

Expected result

records/report-clean.txt shows PASS on every test line. No FAIL entries remain.