if-then-else in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of nested if-then-else in Bash

What is the output of this Bash script when run?

#!/bin/bash
x=5
if [ $x -gt 3 ]; then
  if [ $x -lt 10 ]; then
    echo "Between 4 and 9"
  else
    echo "10 or more"
  fi
else
  echo "3 or less"
fi

Bash Scripting

#!/bin/bash
x=5
if [ $x -gt 3 ]; then
  if [ $x -lt 10 ]; then
    echo "Between 4 and 9"
  else
    echo "10 or more"
  fi
else
  echo "3 or less"
fi

A Between 4 and 9

B 10 or more

C 3 or less

D Syntax error

💡 Hint

Check the conditions step by step and see which echo runs.

The variable x is 5, which is greater than 3 and less than 10, so the inner if condition is true and prints 'Between 4 and 9'.

📝 Syntax

intermediate

Identify the syntax error in this if-then-else script

Which option shows the correct way to fix the syntax error in this Bash script?

#!/bin/bash
x=10
if [ $x -eq 10 ]
  echo "x is 10"
else
  echo "x is not 10"
fi

Bash Scripting

#!/bin/bash
x=10
if [ $x -eq 10 ]
  echo "x is 10"
else
  echo "x is not 10"
fi

A Add 'then' after the if condition: if [ $x -eq 10 ]; then

B Add a semicolon after echo statement

C Replace 'fi' with 'end'

D Remove the else block

💡 Hint

Bash requires 'then' after the if condition.

The if statement must be followed by 'then' to be syntactically correct.

🔧 Debug

advanced

Why does this if-then-else script always print 'No'?

Consider this Bash script:

#!/bin/bash
var=""
if [ $var ]; then
  echo "Yes"
else
  echo "No"
fi

Why does it always print "No" even if var is empty?

Bash Scripting

#!/bin/bash
var=""
if [ $var ]; then
  echo "Yes"
else
  echo "No"
fi

A Because the script has a syntax error

B Because [ $var ] is false when var is empty, so else runs

C Because var is not defined

D Because echo is not inside the if block

💡 Hint

Check how Bash treats empty strings inside [ ]

In Bash, [ $var ] tests if $var is non-empty. If empty, condition is false and else runs.

🚀 Application

advanced

What is the output of this if-then-else with arithmetic test?

What does this Bash script print?

#!/bin/bash
num=7
if (( num % 2 == 0 )); then
  echo "Even"
else
  echo "Odd"
fi

Bash Scripting

#!/bin/bash
num=7
if (( num % 2 == 0 )); then
  echo "Even"
else
  echo "Odd"
fi

A Syntax error

B Even

C Odd

D No output

💡 Hint

Check if 7 is divisible by 2

7 modulo 2 is 1, so condition is false and else block prints 'Odd'.

🧠 Conceptual

expert

How many times does this loop print 'Hello'?

Analyze this Bash script:

#!/bin/bash
count=0
while [ $count -lt 3 ]; do
  if [ $count -eq 1 ]; then
    count=$((count + 2))
  else
    count=$((count + 1))
  fi
  echo "Hello"
done

How many times will "Hello" be printed?

Bash Scripting

#!/bin/bash
count=0
while [ $count -lt 3 ]; do
  if [ $count -eq 1 ]; then
    count=$((count + 2))
  else
    count=$((count + 1))
  fi
  echo "Hello"
done

A 4

B 3

C Infinite loop

D 2

💡 Hint

Trace the value of count each loop iteration.

Loop runs while count < 3. Iterations: count=0 -> print, count=1 -> print and add 2 (count=3), loop ends. So prints twice.

Practice

1. What does the if-then-else structure do in a bash script?

easy

A. It comments out lines in the script.

B. It repeats a set of commands multiple times.

C. It defines a function to reuse code.

D. It lets the script choose between two paths based on a condition.

Solution

1. Step 1: Understand the purpose of if-then-else

   The if-then-else structure checks a condition and runs code based on whether the condition is true or false.

2. Step 2: Compare with other options

   Repeating commands is done with loops, functions reuse code, and comments do not execute code.

3. Final Answer:

   It lets the script choose between two paths based on a condition. -> Option D

4. Quick Check:

   if-then-else = choose path [OK]

Hint: If you see a condition, it's likely if-then-else [OK]

Common Mistakes:

• Confusing if-then-else with loops
• Thinking if-then-else defines functions
• Mixing comments with control flow

2. Which of the following is the correct syntax to start an if statement in bash?

easy

A. if [ condition ]; then

B. if { condition } then

C. if(condition) then

D. if condition then

Solution

1. Step 1: Recall bash if syntax

   Bash requires spaces around brackets and a semicolon before then: if [ condition ]; then.

2. Step 2: Check other options

   if(condition) then misses spaces and semicolon, B uses braces incorrectly, D misses brackets and semicolon.

3. Final Answer:

   if [ condition ]; then -> Option A

4. Quick Check:

   Spaces and semicolon needed [OK]

Hint: Remember spaces around [ ] and semicolon before then [OK]

Common Mistakes:

• No spaces around brackets
• Missing semicolon before then
• Using parentheses or braces incorrectly

3. What will be the output of this script?

#!/bin/bash
x=5
if [ $x -gt 3 ]; then
  echo "Greater"
else
  echo "Smaller"
fi

medium

A. No output

B. Smaller

C. Greater

D. Syntax Error

Solution

1. Step 1: Evaluate the condition

   The condition checks if x (5) is greater than 3, which is true.

2. Step 2: Determine which branch runs

   Since condition is true, the script prints "Greater".

3. Final Answer:

   Greater -> Option C

4. Quick Check:

   5 > 3 = Greater [OK]

Hint: Check numeric comparison carefully [OK]

Common Mistakes:

• Confusing -gt with -lt
• Missing spaces causing syntax errors
• Assuming else runs when condition is true

4. Find the error in this script:

#!/bin/bash
if [ $num -eq 10 ]
  echo "Ten"
else
  echo "Not Ten"
fi

medium

A. Missing then after condition

B. Wrong comparison operator

C. Missing fi at the end

D. No error

Solution

1. Step 1: Check if statement syntax

   The if condition must be followed by then keyword to start the true block.

2. Step 2: Identify missing part

   The script misses then after the condition line.

3. Final Answer:

   Missing then after condition -> Option A

4. Quick Check:

   if needs then [OK]

Hint: Always put then after condition in if [ ] [OK]

Common Mistakes:

• Forgetting then keyword
• Using wrong comparison operators
• Missing fi to close if

5. You want a script that prints "Even" if a number is even, and "Odd" if it is odd. Which script correctly uses if-then-else to do this?

num=4
# Choose correct script

hard

A. if [ $num % 2 -eq 0 ]; then
echo "Even"
else
echo "Odd"
fi

B. if (( num % 2 == 0 )); then
echo "Even"
else
echo "Odd"
fi

C. if [ $num % 2 == 0 ]; then
echo "Even"
else
echo "Odd"
fi

D. if [ $num / 2 -eq 0 ]; then
echo "Even"
else
echo "Odd"
fi

Solution

1. Step 1: Understand arithmetic evaluation in bash

   Using double parentheses (( )) allows arithmetic expressions and comparisons directly.

2. Step 2: Check each option

   if [ $num % 2 -eq 0 ]; then echo "Even" else echo "Odd" fi uses % inside [ ] without arithmetic evaluation. if [ $num % 2 == 0 ]; then echo "Even" else echo "Odd" fi uses % inside [ ] without arithmetic evaluation. if [ $num / 2 -eq 0 ]; then echo "Even" else echo "Odd" fi uses / instead of % for modulus. if (( num % 2 == 0 )); then echo "Even" else echo "Odd" fi correctly uses (( )) with modulus and comparison.

3. Final Answer:

   if (( num % 2 == 0 )); then echo "Even" else echo "Odd" fi -> Option B

4. Quick Check:

   Use (( )) for arithmetic if [OK]

Hint: Use (( )) for math conditions in bash [OK]

Common Mistakes:

• Using [ ] with arithmetic operators incorrectly
• Confusing / with % for modulus
• Missing then keyword