Shell concept (Bash, Zsh) in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this Bash command?

Consider the following command run in Bash shell:

echo $((3 + 5 * 2))

What will be printed on the screen?

Linux CLI

echo $((3 + 5 * 2))

A 13

B 16

C 10

D Error: invalid arithmetic expression

💡 Hint

Remember the order of operations in arithmetic expressions.

In arithmetic, multiplication happens before addition. So 5 * 2 = 10, then 3 + 10 = 13.

📝 Syntax

intermediate

Which option correctly defines a function in Bash?

You want to create a function named greet that prints 'Hello'. Which of these is the correct syntax?

A function greet { echo 'Hello'; }

B def greet() { echo 'Hello' }

C greet() echo 'Hello'

D function greet() echo 'Hello';

💡 Hint

Bash functions can be declared with or without the 'function' keyword, but syntax matters.

Option A uses the correct Bash syntax: 'function name { commands; }'. Other options have syntax errors or use other languages' syntax.

🔧 Debug

advanced

Why does this script fail to print the variable value?

Given this script:

#!/bin/bash VAR=5 if [ $VAR -gt 3 ] then echo "Value is $var" fi

What is the reason for the output being empty?

Linux CLI

#!/bin/bash
VAR=5
if [ $VAR -gt 3 ]
then
  echo "Value is $var"
fi

A The script lacks execution permission, so it doesn't run.

B Variable names are case-sensitive; $var is empty because VAR was set, not var.

C The if condition syntax is wrong; it should use double brackets [[ ]].

D The echo command is missing quotes around $var.

💡 Hint

Check how variable names are written and used.

Bash variables are case-sensitive. VAR and var are different. The script sets VAR but prints $var, which is empty.

🚀 Application

advanced

Which command lists all files including hidden ones in long format sorted by modification time?

You want to see all files, including hidden ones (those starting with a dot), in your current directory. You want the list in long format and sorted by newest modified first. Which command achieves this?

A ls -l -a -t

B ls -ltr

C ls -lat

D ls -l -a -r -t

💡 Hint

Check what each option means: -l, -a, -t, -r

-l shows long format, -a shows hidden files, -t sorts by modification time newest first, -r reverses order. So -lat lists all files long format sorted newest first.

🧠 Conceptual

expert

What happens when you run this pipeline in Bash?

Consider this command:

echo 'apple banana cherry' | while read word; do echo $word; done

What will be the output?

A

apple
banana
cherry

B

apple banana cherry
apple banana cherry

C No output, the loop does not run

D apple

💡 Hint

Think about how 'read' works with default IFS and how the pipeline feeds input.

The 'read word' command splits the input line on whitespace (default IFS=space/tab/newline), assigning only the first field 'apple' to 'word'. The rest ('banana cherry') is discarded. Since there's only one line, the loop runs once.

Practice

1. What is a shell in Linux or macOS?

easy

A. A programming language for creating websites

B. A program that lets you type commands to control your computer

C. A graphical interface for editing photos

D. A type of hardware component inside the computer

Solution

1. Step 1: Understand the role of a shell

   A shell is a program that takes your typed commands and runs them on the computer.

2. Step 2: Compare options

   Options A, B, and C describe web programming, hardware, and graphics, which are not shells.

3. Final Answer:

   A program that lets you type commands to control your computer -> Option B

4. Quick Check:

   Shell = command program [OK]

Hint: Shell = command line program to control computer [OK]

Common Mistakes:

• Thinking shell is hardware
• Confusing shell with graphical apps
• Mixing shell with programming languages

2. Which of these is the correct way to run a command with an option in Bash?

easy

A. ls -ll

B. ls -l -

C. ls l-

D. ls -l

Solution

1. Step 1: Identify correct option syntax

   Options start with a dash (-) followed by letters, so '-l' is correct.

2. Step 2: Check each option

   A: 'ls -l' is correct. B has extra dash, C has wrong order, D uses '-ll' which repeats the option unnecessarily.

3. Final Answer:

   ls -l -> Option D

4. Quick Check:

   Options start with dash and letter [OK]

Hint: Options start with dash (-) followed by letters [OK]

Common Mistakes:

• Adding extra dash after options
• Writing options without dash
• Combining options incorrectly

3. What will the following Bash command output?

echo "Hello"; echo "World"

medium

A. Hello
World (two lines)

B. Hello\nWorld

C. Hello
World

D. Hello World

Solution

1. Step 1: Understand the echo command

   Each echo prints its argument followed by a new line by default.

2. Step 2: Analyze the command sequence

   First echo prints 'Hello' then newline, second echo prints 'World' then newline, so output is two lines.

3. Final Answer:

   Hello World (two lines) -> Option A

4. Quick Check:

   echo prints with newline [OK]

Hint: echo prints text then newline by default [OK]

Common Mistakes:

• Thinking echo joins output on one line
• Confusing literal \n with newline
• Ignoring semicolon separates commands

4. What is wrong with this Bash script snippet?

for i in 1 2 3
do
echo $i
done

medium

A. Missing semicolon after '3'

B. Incorrect loop syntax, should use parentheses

C. No error, script runs fine

D. Missing 'do' keyword

Solution

1. Step 1: Check for loop syntax

   The for loop syntax 'for i in 1 2 3; do ... done' is correct. The semicolon after '3' is optional if 'do' is on next line.

2. Step 2: Verify keywords and structure

   'do' is present, parentheses are not needed in Bash for this loop, so no syntax error.

3. Final Answer:

   No error, script runs fine -> Option C

4. Quick Check:

   Bash for loop syntax correct without semicolon if newline before do [OK]

Hint: Newline before 'do' replaces semicolon in for loops [OK]

Common Mistakes:

• Thinking semicolon is always required
• Confusing Bash syntax with other languages
• Missing 'do' keyword

5. You want to list all files in a directory including hidden ones, sorted by modification time. Which command should you use?

hard

A. ls -a -t

B. ls -l -h

C. ls -r -S

D. ls -d .*

Solution

1. Step 1: Understand options needed

   '-a' shows all files including hidden, '-t' sorts by modification time.

2. Step 2: Evaluate each option

   A: 'ls -r -S' reverses and sorts by size (no hidden). B: 'ls -l -h' long format with human sizes (no hidden, no time sort). C: 'ls -a -t' shows all including hidden, sorted by mod time. D: 'ls -d .*' shows only dot entries.

3. Final Answer:

   ls -a -t -> Option A

4. Quick Check:

   Show hidden + sort by time = ls -a -t [OK]

Hint: Use -a for hidden, -t for time sort [OK]

Common Mistakes:

• Using -l instead of -a to show hidden
• Confusing -S (size) with -t (time)
• Using -d .* lists only hidden files