sort and uniq in Linux CLI - Mini Project: Build & Apply

Sort and Uniq Command Practice

📖 Scenario: You have a list of fruit names with some duplicates. You want to organize this list by sorting it alphabetically and removing duplicates to get a clean list.

🎯 Goal: Learn how to use the sort and uniq commands together to sort a list and remove duplicate entries.

📋 What You'll Learn

Create a file named fruits.txt with the exact fruit names given.

Use the sort command to sort the fruit names alphabetically.

Use the uniq command to remove duplicate fruit names after sorting.

Display the final sorted and unique list on the terminal.

💡 Why This Matters

🌍 Real World

Cleaning and organizing lists of data like names, products, or logs is common in daily computer tasks.

💼 Career

Many IT and data jobs require sorting and filtering text data quickly using command line tools.

1

Create the fruits.txt file

Create a file named fruits.txt containing these exact lines in this order: apple, banana, apple, orange, banana, grape.

Linux CLI

# Create the file fruits.txt with the fruit names
# Your code here

Hint

Use echo with -e and newline characters \n to create the file.

2

Sort the fruits.txt file

Use the sort command on fruits.txt and save the output to a new file called sorted_fruits.txt.

Linux CLI

echo -e "apple\nbanana\napple\norange\nbanana\ngrape" > fruits.txt
# Sort fruits.txt and save to sorted_fruits.txt
# Your code here

Hint

Use sort fruits.txt > sorted_fruits.txt to save sorted output.

3

Remove duplicates with uniq

Use the uniq command on sorted_fruits.txt and save the output to a new file called unique_fruits.txt.

Linux CLI

echo -e "apple\nbanana\napple\norange\nbanana\ngrape" > fruits.txt
sort fruits.txt > sorted_fruits.txt
# Use uniq on sorted_fruits.txt and save to unique_fruits.txt
# Your code here

Hint

Use uniq sorted_fruits.txt > unique_fruits.txt to remove duplicates.

4

Display the final unique sorted list

Use the cat command to display the contents of unique_fruits.txt on the terminal.

Linux CLI

echo -e "apple\nbanana\napple\norange\nbanana\ngrape" > fruits.txt
sort fruits.txt > sorted_fruits.txt
uniq sorted_fruits.txt > unique_fruits.txt
# Display the contents of unique_fruits.txt
# Your code here

Hint

Use cat unique_fruits.txt to show the final list.

Practice

1. What does the uniq command do when used alone on a text file?

easy

A. Deletes all empty lines

B. Removes repeated adjacent lines

C. Counts all lines in the file

D. Sorts all lines alphabetically

Solution

1. Step 1: Understand the uniq command behavior

   The uniq command filters out repeated lines only if they are next to each other.

2. Step 2: Compare with other options

   It does not sort lines or count all lines; it only removes adjacent duplicates.

3. Final Answer:

   Removes repeated adjacent lines -> Option B

4. Quick Check:

   uniq removes adjacent duplicates = D [OK]

Hint: uniq only removes duplicates if they are next to each other [OK]

Common Mistakes:

• Thinking uniq sorts lines
• Assuming uniq removes all duplicates anywhere
• Confusing uniq with wc (word count)

2. Which of the following is the correct syntax using a pipe to sort a file named data.txt and remove duplicate lines?

easy

A. sort data.txt | uniq

B. uniq data.txt | sort

C. sort -u data.txt

D. uniq -s data.txt

Solution

1. Step 1: Understand the order of commands

   To remove duplicates correctly, lines must be sorted first so duplicates become adjacent.

2. Step 2: Check each option

   sort data.txt | uniq sorts then pipes to uniq, which removes adjacent duplicates. uniq data.txt | sort runs uniq first, which won't remove all duplicates if unsorted. sort -u data.txt uses sort -u which is valid but not the pipe syntax asked. uniq -s data.txt is invalid syntax.

3. Final Answer:

   sort data.txt | uniq -> Option A

4. Quick Check:

   Sort before uniq to remove duplicates = A [OK]

Hint: Always sort before uniq to remove duplicates correctly [OK]

Common Mistakes:

• Running uniq before sort
• Using invalid uniq options
• Confusing sort -u with uniq

3. Given a file names.txt with contents:

bob
alice
bob
carol
alice
bob

What is the output of sort names.txt | uniq?

medium

A. alice
bob
carol

B. bob
alice
carol

C. alice
bob
bob
carol
alice
bob

D. bob
carol
alice

Solution

1. Step 1: Sort the file lines

   Sorting the lines alphabetically gives: alice, alice, bob, bob, bob, carol.

2. Step 2: Apply uniq to remove adjacent duplicates

   uniq removes repeated adjacent lines, so only one of each remains: alice, bob, carol.

3. Final Answer:

   alice bob carol -> Option A

4. Quick Check:

   Sort then uniq removes duplicates = alice, bob, carol [OK]

Hint: Sort first, then uniq removes duplicates in order [OK]

Common Mistakes:

• Not sorting before uniq
• Expecting uniq to remove all duplicates anywhere
• Confusing output order

4. You run sort data.txt | uniq but notice duplicates remain. What is the most likely cause?

medium

A. sort command does not work on text files

B. uniq command is misspelled

C. The file contains lines with trailing spaces or tabs

D. The file is empty

Solution

1. Step 1: Understand how sort and uniq treat whitespace

   sort and uniq treat lines with trailing spaces or tabs as different lines, so duplicates with extra spaces won't be adjacent identical.

2. Step 2: Check other options

   uniq misspelling would cause error, not duplicates remaining. sort works on text files. Empty file means no duplicates.

3. Final Answer:

   The file contains lines with trailing spaces or tabs -> Option C

4. Quick Check:

   Trailing spaces cause uniq to miss duplicates = C [OK]

Hint: Check for trailing spaces if duplicates remain after sort|uniq [OK]

Common Mistakes:

• Assuming uniq always removes duplicates regardless of spaces
• Ignoring trailing whitespace differences
• Thinking sort fails on text files

5. You want to count how many unique IP addresses appear in access.log. Which command correctly sorts, removes duplicates, and counts unique lines?

hard

A. sort access.log | uniq -c

B. uniq access.log | wc -l

C. uniq -c access.log | sort

D. sort -u access.log | wc -l

Solution

1. Step 1: Understand the goal

   You want the count of unique IP addresses, so you need to remove duplicates and count the unique lines.

2. Step 2: Analyze each option

   sort access.log | uniq -c counts occurrences but does not sum total unique lines. uniq -c access.log | sort counts duplicates before sorting, so misses some. sort -u access.log | wc -l uses sort -u to get unique lines, then counts lines with wc -l, which gives the unique count. uniq access.log | wc -l counts lines after uniq without sorting, so duplicates may remain.

3. Final Answer:

   sort -u access.log | wc -l -> Option D

4. Quick Check:

   sort -u then wc -l counts unique lines = B [OK]

Hint: Use sort -u then wc -l to count unique lines fast [OK]

Common Mistakes:

• Using uniq -c without sorting first
• Counting lines before removing duplicates
• Confusing uniq -c output with total unique count