while loop in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of a simple while loop counting down

What is the output of this Bash script?

Bash Scripting

count=3
while [ $count -gt 0 ]
do
  echo $count
  count=$((count - 1))
done

A

3
2
1

B

3
2
1
0

C

1
2
3

D

0
1
2
3

💡 Hint

Remember the loop runs while count is greater than zero and decreases count each time.

The loop starts with count=3 and prints it, then decreases count by 1 until count is no longer greater than 0. So it prints 3, 2, 1.

💻 Command Output

intermediate

While loop with a break condition

What will this Bash script output?

Bash Scripting

i=1
while true
 do
  echo $i
  if [ $i -eq 3 ]; then
    break
  fi
  i=$((i + 1))
done

A

1
2

B

1
2
3
4

C

1
2
3

D

1
2
3
4
5

💡 Hint

The loop breaks when i equals 3.

The loop prints i starting from 1, increments i, and breaks when i reaches 3, so it prints 1, 2, 3.

📝 Syntax

advanced

Identify the syntax error in this while loop

Which option shows the correct syntax to fix the error in this Bash while loop?

Bash Scripting

count=5
while [ $count -gt 0 ]
  echo $count
  count=$((count - 1))
done

A

Add 'do' after the while condition:
while [ $count -gt 0 ]; do

B Replace 'done' with 'end'

C Remove the square brackets from the condition

D Add a semicolon after 'done'

💡 Hint

A while loop in Bash requires a 'do' keyword after the condition.

The 'do' keyword is mandatory after the while condition to start the loop body. Without it, the script has a syntax error.

🔧 Debug

advanced

Why does this while loop run infinitely?

This script runs forever. What is the reason?

Bash Scripting

num=1
while [ $num -le 3 ]
do
  echo $num
done

A The echo command causes the loop to restart

B Variable 'num' is never updated inside the loop

C Missing 'do' keyword after while condition

D The condition uses '-le' which is invalid

💡 Hint

Check if the loop changes the variable controlling the condition.

The variable 'num' is never incremented, so the condition is always true, causing an infinite loop.

🚀 Application

expert

Create a while loop to read lines from a file

Which script correctly reads each line from 'input.txt' and prints it?

A

while read line; do
  echo $line
  done > input.txt

B

while [ read line ]; do
  echo $line
done < input.txt

C

while read line
  echo $line
done < input.txt

D

while read line; do
  echo "$line"
done < input.txt

💡 Hint

The 'read' command reads a line, and the loop must redirect input from the file.

Option D correctly uses 'while read line; do ... done < input.txt' to read and print each line. Others have syntax errors or wrong redirection.