Unique Lines: uniq

The uniq command removes adjacent duplicate lines. This is a key detail: it only works on lines that are next to each other. That is why you almost always sort first, then pipe to uniq.

sort access.log | uniq

This removes all duplicates and prints each unique line once.

Counting duplicates with -c

sort access.log | uniq -c

      3 deck 1
      1 deck 3
      2 deck 7

Each line is prefixed with how many times it appeared. This is an incredibly useful pattern for quick data analysis.

Why sort first?

Without sorting, uniq only collapses runs of identical lines:

alpha
alpha    ← removed (adjacent duplicate)
beta
alpha    ← NOT removed (not adjacent)

The sort | uniq combo is so common it deserves its own muscle memory.

Mission: Door Access Audit

Security flagged unusual activity on Deck 7. The file door_access.log records every crew member who swiped through the door. Find out who has been coming and going the most, and file the tally.

1. Combine sort and uniq -c through a pipe on door_access.log to count how many times each crew member accessed the door, and display it.
2. Save that tally into a new file called access-tally.txt.
3. Create a folder called security and move access-tally.txt into it.
4. Search the tally for Voss to confirm the crew member with the most entries.

Expected result

security/access-tally.txt holds each name once, prefixed by its access count; Voss has the most (3).