sort and uniq in Linux CLI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the sort command do in Linux?

The sort command arranges lines of text in a file or input alphabetically or numerically. It helps organize data so it's easier to read or process.

beginner

What is the purpose of the uniq command?

uniq filters out repeated lines that are next to each other in a file or input. It shows only one copy of each repeated line.

beginner

Why do you often use sort before uniq?

Because uniq only removes duplicates that are next to each other, sorting first groups duplicates together so uniq can remove all repeated lines.

intermediate

How do you count how many times each line appears using uniq?

Use uniq -c. It adds a number before each line showing how many times that line appeared consecutively.

beginner

What does the command sort file.txt | uniq do?

It sorts the lines in file.txt alphabetically, then removes any duplicate lines, showing only unique lines in order.

What happens if you run uniq file.txt without sorting first?

A Only consecutive duplicate lines are removed

B All duplicate lines are removed regardless of position

C The file is sorted alphabetically

D Nothing happens

uniq only removes duplicates that are next to each other. Without sorting, duplicates separated by other lines stay.

Which command shows how many times each line appears in a sorted file?

A uniq -c file.txt

B sort file.txt | uniq -c

C sort -c file.txt

D uniq file.txt

Sorting first groups duplicates, then uniq -c counts each group.

What does sort -r do?

A Sorts lines in reverse order

B Removes duplicates

C Counts lines

D Sorts lines randomly

-r option sorts lines in reverse (descending) order.

How can you remove duplicate lines ignoring case differences?

A sort | uniq

B sort -n

C uniq -c

D sort -f | uniq -i

sort -f ignores case, and uniq -i ignores case when filtering duplicates.

What is the output of echo -e "apple\nApple\napple" | sort | uniq?

A apple

B apple Apple apple

C Apple apple

D Apple

Sorting puts 'Apple' before 'apple'. uniq sees them as different because of case, so both appear.

Explain how to use sort and uniq together to find unique lines in a file.

Think about why sorting helps uniq work better.

Describe how to count the number of times each unique line appears in a text file using Linux commands.

Counting needs grouping first.