sort and uniq in pipelines in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this pipeline?

Consider a file fruits.txt with the following lines:

apple
banana
apple
orange
banana
banana

What is the output of this command?

cat fruits.txt | sort | uniq

Bash Scripting

cat fruits.txt | sort | uniq

A

apple
banana
banana
orange

B

apple
apple
banana
banana
banana
orange

C

apple
banana
orange

D

banana
apple
orange

💡 Hint

Think about what sort and uniq do when combined.

The sort command arranges lines alphabetically. Then uniq removes consecutive duplicate lines. So duplicates are removed after sorting, leaving one of each fruit.

💻 Command Output

intermediate

What does this pipeline output?

Given a file colors.txt with:

red
blue
red
green
blue
blue

What is the output of:

cat colors.txt | uniq | sort

Bash Scripting

cat colors.txt | uniq | sort

A

blue
blue
green
red
red

B

red
blue
green

C

red
blue
red
green
blue
blue

D

red
green
blue

💡 Hint

Remember that uniq only removes adjacent duplicates.

The uniq command removes only consecutive duplicates, so the first uniq keeps the first 'red' and removes the second only if adjacent. Then sort arranges lines alphabetically.

📝 Syntax

advanced

Which pipeline correctly counts unique lines ignoring case?

You want to count how many unique lines are in data.txt, ignoring case differences. Which command pipeline does this correctly?

A cat data.txt | sort -f | uniq -i | wc -l

B cat data.txt | sort | uniq -i | wc -l

C cat data.txt | uniq -i | sort | wc -l

D cat data.txt | sort -f | uniq | wc -l

💡 Hint

Check which commands support case-insensitive options and how they affect sorting and uniqueness.

sort -f sorts ignoring case, grouping lines that match ignoring case together. uniq -i then removes consecutive duplicates ignoring case. wc -l counts the remaining unique lines ignoring case.

🔧 Debug

advanced

Why does this pipeline not remove all duplicates?

You run this command:

cat list.txt | uniq | sort

But you notice duplicates remain in the output. Why?

A Because <code>cat</code> removes duplicates before piping.

B Because <code>uniq</code> only removes adjacent duplicates, and sorting after <code>uniq</code> does not group duplicates together.

C Because <code>uniq</code> requires the <code>-d</code> option to remove duplicates.

D Because <code>sort</code> does not work on piped input.

💡 Hint

Think about the order of commands and how uniq works.

uniq only removes duplicates if they are next to each other. Since sorting happens after uniq, duplicates may be separated and not removed.

🚀 Application

expert

How to find the top 3 most frequent words in a file?

You have a file words.txt with many words, one per line. You want to find the top 3 most frequent words along with their counts. Which pipeline achieves this?

A cat words.txt | sort | uniq | sort -nr | head -3

B cat words.txt | uniq -c | sort -nr | head -3

C cat words.txt | sort -nr | uniq -c | head -3

D cat words.txt | sort | uniq -c | sort -nr | head -3

💡 Hint

Count duplicates after sorting, then sort counts numerically in reverse order.

First, sort groups identical words together. Then uniq -c counts occurrences. Next, sort -nr sorts by count descending. Finally, head -3 shows top 3.