sort and uniq in pipelines in Bash Scripting - Mini Project: Build & Apply

Using sort and uniq in pipelines

📖 Scenario: You work in a small office where you receive a list of names with duplicates. You want to clean this list by sorting the names alphabetically and removing duplicates.

🎯 Goal: Build a bash script pipeline that sorts a list of names and removes duplicates using sort and uniq.

📋 What You'll Learn

Create a file named names.txt with a list of names including duplicates

Use a variable to hold the filename

Use a pipeline with sort and uniq to process the file

Print the final sorted and unique list of names

💡 Why This Matters

🌍 Real World

Cleaning and organizing lists of data like names, emails, or product IDs is common in office work and scripting tasks.

💼 Career

Knowing how to use pipelines with <code>sort</code> and <code>uniq</code> is a basic but essential skill for system administrators, data analysts, and anyone working with text data on the command line.

1

Create the names file

Create a file called names.txt with these exact names, each on its own line: Alice, Bob, Charlie, Alice, Bob, David

Bash Scripting

# Create the file names.txt with the given names
# Your code here

Hint

Use echo -e with newline characters \n and redirect output to names.txt.

2

Set the filename variable

Create a variable called filename and set it to the string names.txt

Bash Scripting

echo -e "Alice\nBob\nCharlie\nAlice\nBob\nDavid" > names.txt
# Create a variable filename with value 'names.txt'
# Your code here

Hint

Use filename="names.txt" to assign the variable.

3

Sort and remove duplicates using a pipeline

Use a pipeline with sort and uniq commands to read from the file stored in filename and produce a sorted list without duplicates. Store the result in a variable called clean_names

Bash Scripting

echo -e "Alice\nBob\nCharlie\nAlice\nBob\nDavid" > names.txt
filename="names.txt"
# Use sort and uniq in a pipeline to read from $filename and save to clean_names
# Your code here

Hint

Use command substitution with $( ) to save the pipeline output to clean_names.

4

Print the cleaned list

Print the variable clean_names to display the sorted list of unique names

Bash Scripting

echo -e "Alice\nBob\nCharlie\nAlice\nBob\nDavid" > names.txt
filename="names.txt"
clean_names=$(sort "$filename" | uniq)
# Print the clean_names variable
# Your code here

Hint

Use echo "$clean_names" to print the variable preserving line breaks.

Practice

1. What is the main purpose of using sort | uniq together in a bash pipeline?

easy

A. To get a sorted list with duplicates removed

B. To count the number of lines in a file

C. To sort lines but keep duplicates

D. To find the longest line in a file

Solution

1. Step 1: Understand what sort does

   The sort command arranges lines in alphabetical or numerical order.

2. Step 2: Understand what uniq does after sorting

   The uniq command removes duplicate adjacent lines, so sorting first groups duplicates together for removal.

3. Final Answer:

   To get a sorted list with duplicates removed -> Option A

4. Quick Check:

   sort + uniq = sorted unique lines [OK]

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

Common Mistakes:

• Using uniq before sort, which misses duplicates
• Thinking uniq counts lines instead of removing duplicates
• Assuming sort removes duplicates by itself

2. Which of the following is the correct syntax to remove duplicate lines from file.txt and sort the output?

easy

A. uniq file.txt | sort

B. sort file.txt | uniq

C. sort | uniq file.txt

D. uniq | sort file.txt

Solution

1. Step 1: Identify correct command order

   The file must be sorted first, so sort file.txt comes before uniq.

2. Step 2: Check syntax correctness

   sort file.txt | uniq correctly pipes sorted output to uniq for duplicate removal.

3. Final Answer:

   sort file.txt | uniq -> Option B

4. Quick Check:

   sort first, then uniq = correct syntax [OK]

Hint: Pipe sorted output into uniq: sort file | uniq [OK]

Common Mistakes:

• Placing uniq before sort, which fails to remove all duplicates
• Incorrect pipe placement causing syntax errors
• Trying to pass file as argument to uniq instead of sort

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
bob
carol
alice
bob

B. bob
alice
carol

C. bob
carol
alice

D. alice
bob
carol

Solution

1. Step 1: Sort the file contents

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

2. Step 2: Apply uniq to remove duplicates

   Uniq removes repeated adjacent lines, resulting in: alice, bob, carol.

3. Final Answer:

   alice\nbob\ncarol -> Option D

4. Quick Check:

   sort + uniq = unique sorted lines [OK]

Hint: Sort first to group duplicates, then uniq removes repeats [OK]

Common Mistakes:

• Not sorting first, so uniq misses duplicates
• Expecting original order instead of sorted
• Confusing uniq output with counting duplicates

4. You run uniq file.txt | sort to remove duplicates and sort lines, but duplicates remain. What is the likely problem?

medium

A. uniq only removes adjacent duplicates, so sorting after uniq misses duplicates

B. sort command is not working without options

C. file.txt is empty, so no output

D. uniq requires -c option to remove duplicates

Solution

1. Step 1: Understand uniq behavior

   Uniq removes only adjacent duplicate lines, so if duplicates are scattered, it won't remove them.

2. Step 2: Analyze command order effect

   Sorting after uniq means duplicates are not grouped before uniq runs, so duplicates remain.

3. Final Answer:

   uniq only removes adjacent duplicates, so sorting after uniq misses duplicates -> Option A

4. Quick Check:

   uniq needs sorted input to remove all duplicates [OK]

Hint: Sort before uniq to group duplicates for removal [OK]

Common Mistakes:

• Thinking uniq removes all duplicates regardless of order
• Believing sort alone removes duplicates
• Using uniq -c instead of uniq for removal

5. You have a log file access.log with many repeated IP addresses scattered randomly. You want a sorted list of unique IPs. Which command pipeline correctly achieves this?

hard

A. cat access.log | uniq | sort

B. uniq access.log | sort

C. sort -u access.log

D. uniq access.log | sort -u

Solution

1. Step 1: Understand sort -u option

   sort -u sorts and removes duplicates in one step efficiently.

2. Step 2: Why others fail

   Options A, B, and D all apply uniq before sorting, missing non-adjacent duplicates since IPs are scattered randomly.

3. Final Answer:

   sort -u access.log -> Option C

4. Quick Check:

   sort -u = sorted unique lines in one command [OK]

Hint: Use sort -u for sorted unique lines in one step [OK]

Common Mistakes:

• Using uniq before sort, missing duplicates
• Not knowing sort -u combines sorting and uniqueness
• Using unnecessary cat command