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

Challenge - 5 Problems

💻 Command Output

intermediate

Output of a simple if-elif-else script

What is the output of this Bash script when run with argument 15?

Bash Scripting

#!/bin/bash
num=$1
if [ "$num" -lt 10 ]; then
  echo "Less than 10"
elif [ "$num" -lt 20 ]; then
  echo "Between 10 and 19"
else
  echo "20 or more"
fi

A Less than 10

B Syntax error

C 20 or more

D Between 10 and 19

💡 Hint

Check the numeric comparison operators and the order of conditions.

The script checks if the number is less than 10, then less than 20. Since 15 is not less than 10 but less than 20, it prints 'Between 10 and 19'.

🔧 Debug

intermediate

Identify the error in this if-elif-else script

What error will this Bash script produce when run?

Bash Scripting

#!/bin/bash
num=5
if [ $num < 10 ]; then
  echo "Less than 10"
elif [ $num < 20 ]; then
  echo "Between 10 and 19"
else
  echo "20 or more"
fi

A Runs correctly and prints 'Less than 10'

B Syntax error due to incorrect comparison operator

C Runtime error: command not found

D Prints '20 or more'

💡 Hint

Check the comparison operators used inside the test brackets.

In Bash, '<' is a redirection operator, not a numeric comparison. The correct operator is '-lt'. Using '<' causes a syntax error.

🚀 Application

advanced

Script to categorize a number with if-elif-else

Which script correctly categorizes a number into 'small' (less than 5), 'medium' (5 to 10), or 'large' (greater than 10)?

A

#!/bin/bash
num=$1
if [ "$num" -lt 5 ]; then
  echo "small"
elif [ "$num" -le 10 ]; then
  echo "medium"
else
  echo "large"
fi

B

#!/bin/bash
num=$1
if [ "$num" -le 5 ]; then
  echo "small"
elif [ "$num" -lt 10 ]; then
  echo "medium"
else
  echo "large"
fi

C

#!/bin/bash
num=$1
if [ "$num" -lt 5 ]; then
  echo "small"
elif [ "$num" -lt 10 ]; then
  echo "medium"
else
  echo "large"
fi

D

#!/bin/bash
num=$1
if [ "$num" -lt 5 ]; then
  echo "small"
elif [ "$num" -gt 10 ]; then
  echo "medium"
else
  echo "large"
fi

💡 Hint

Check the numeric ranges carefully and the operators used.

Option A correctly uses '-lt 5' for small, '-le 10' for medium (including 5 to 10), and else for large. Others misclassify or overlap ranges.

🧠 Conceptual

advanced

Understanding else placement in if-elif-else

What happens if you omit the else block in an if-elif-else chain in Bash?

A The script runs but always executes the last elif block

B The script throws a syntax error

C The script runs without errors and does nothing if no conditions match

D The script runs but skips all conditions

💡 Hint

Think about what else does in a conditional chain.

The else block is optional. If omitted and no conditions match, the script simply skips the blocks and continues without error.

💻 Command Output

expert

Output of nested if-elif-else with multiple conditions

What is the output of this script when run with argument 0?

Bash Scripting

#!/bin/bash
num=$1
if [ "$num" -gt 0 ]; then
  if [ "$num" -lt 10 ]; then
    echo "Positive single digit"
  else
    echo "Positive double digit or more"
  fi
elif [ "$num" -eq 0 ]; then
  echo "Zero"
else
  echo "Negative number"
fi

A Zero

B Positive single digit

C Negative number

D Syntax error

💡 Hint

Trace the conditions carefully for input zero.

The script first checks if number is greater than zero (false for 0), then checks if number equals zero (true), so it prints 'Zero'.

Practice

1. What does the if-elif-else structure do in a Bash script?

easy

A. It repeats a set of commands multiple times.

B. It comments out lines of code.

C. It defines a function to reuse code.

D. It lets the script choose between multiple actions based on conditions.

Solution

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

   The if-elif-else structure checks conditions one by one and runs the matching block.

2. Step 2: Compare with other options

   Loops repeat commands, functions reuse code, comments disable code lines. Only if-elif-else chooses actions.

3. Final Answer:

   It lets the script choose between multiple actions based on conditions. -> Option D

4. Quick Check:

   if-elif-else = choose actions [OK]

Hint: If you want choices, use if-elif-else [OK]

Common Mistakes:

• Confusing if-elif-else with loops
• Thinking it defines functions
• Mixing it up with comments

2. Which of the following is the correct syntax to start an if-elif-else block in Bash?

easy

A. if [ condition ]; then

B. if (condition) {

C. if condition then

D. if condition:

Solution

1. Step 1: Recall Bash if syntax

   Bash requires square brackets around conditions and 'then' after the condition, with semicolons or newlines.

2. Step 2: Check each option

   if [ condition ]; then uses correct syntax: if [ condition ]; then. Others use wrong brackets or missing keywords.

3. Final Answer:

   if [ condition ]; then -> Option A

4. Quick Check:

   Correct if syntax = if [ condition ]; then [OK]

Hint: Use brackets and 'then' with semicolon or newline [OK]

Common Mistakes:

• Omitting brackets around condition
• Using parentheses instead of brackets
• Missing 'then' keyword

3. What will be the output of this script?

#!/bin/bash
num=7
if [ $num -lt 5 ]; then
  echo "Less than 5"
elif [ $num -eq 7 ]; then
  echo "Equal to 7"
else
  echo "Other"
fi

medium

A. Less than 5

B. Equal to 7

C. Other

D. Syntax Error

Solution

1. Step 1: Check the value of num and conditions

   num=7. First condition checks if num < 5 (false). Second checks if num == 7 (true).

2. Step 2: Determine which block runs

   Since second condition is true, it prints "Equal to 7" and skips else.

3. Final Answer:

   Equal to 7 -> Option B

4. Quick Check:

   num=7 matches elif condition [OK]

Hint: Check conditions top to bottom, first true runs [OK]

Common Mistakes:

• Assuming first condition runs
• Confusing -lt and -eq operators
• Missing fi causes syntax error

4. Identify the error in this Bash script snippet:

if [ $value -gt 10 ]
  echo "Greater than 10"
elif [ $value -eq 10 ]; then
  echo "Equal to 10"
else
  echo "Less than 10"
fi

medium

A. Missing fi at the end

B. Incorrect use of elif keyword

C. Missing 'then' after first if condition

D. Wrong comparison operator

Solution

1. Step 1: Check syntax after if condition

   In Bash, 'then' must follow the if condition, either on same line after semicolon or next line.

2. Step 2: Verify other parts

   elif has 'then', fi is present, operators are correct. Only missing 'then' after if.

3. Final Answer:

   Missing 'then' after first if condition -> Option C

4. Quick Check:

   if needs 'then' keyword [OK]

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

Common Mistakes:

• Forgetting 'then' after if
• Misplacing semicolons
• Confusing elif syntax

5. You want a script to print "Positive", "Zero", or "Negative" based on a variable num. Which script correctly uses if-elif-else to do this?

hard

A. #!/bin/bash
if [ $num -gt 0 ]; then
echo "Positive"
elif [ $num -eq 0 ]; then
echo "Zero"
else
echo "Negative"
fi

B. #!/bin/bash
if [ $num > 0 ]; then
echo "Positive"
elif [ $num == 0 ]; then
echo "Zero"
else
echo "Negative"
fi

C. #!/bin/bash
if $num > 0 then
echo "Positive"
elif $num == 0 then
echo "Zero"
else
echo "Negative"
fi

D. #!/bin/bash
if [ $num -ge 0 ]; then
echo "Positive"
elif [ $num -eq 0 ]; then
echo "Zero"
else
echo "Negative"
fi

Solution

1. Step 1: Check comparison operators

   Bash uses -gt, -eq, -lt for numeric comparisons. #!/bin/bash if [ $num -gt 0 ]; then echo "Positive" elif [ $num -eq 0 ]; then echo "Zero" else echo "Negative" fi uses correct operators.

2. Step 2: Verify logic and syntax

   #!/bin/bash if [ $num -gt 0 ]; then echo "Positive" elif [ $num -eq 0 ]; then echo "Zero" else echo "Negative" fi correctly checks >0, ==0, else negative. Others use wrong operators or syntax.

3. Final Answer:

   A -> Option A

4. Quick Check:

   Use -gt, -eq for numbers in if-elif-else [OK]

Hint: Use -gt, -eq for numbers; avoid > or == in [ ] [OK]

Common Mistakes:

• Using > or == inside [ ]
• Missing then keyword
• Wrong operator for numeric comparison