until loop in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of a simple until loop

What will be the output of this Bash script?

Bash Scripting

count=1
until [ $count -gt 3 ]
do
  echo $count
  ((count++))
done

A

1
2
3
4

B

1
2
3

C

1
2

D No output

💡 Hint

The loop runs until the condition becomes true, so it stops when count is greater than 3.

The until loop runs while the condition is false. Here, it runs while count is less than or equal to 3, printing 1, 2, and 3.

📝 Syntax

intermediate

Identify the syntax error in the until loop

Which option contains a syntax error in the until loop?

Bash Scripting

count=0
until [ $count -eq 5 ]
  echo $count
  ((count++))
done

A Missing 'do' keyword after until condition

B Incorrect use of ((count++))

C Missing 'done' keyword at the end

D Using -eq instead of -lt in condition

💡 Hint

Check the structure of the until loop syntax.

The 'do' keyword is required after the until condition to start the loop body.

🔧 Debug

advanced

Why does this until loop run infinitely?

Consider this script: count=1 until [ $count -gt 5 ] do echo $count done Why does it run forever?

A The variable 'count' is never incremented inside the loop

B The condition is always true

C The 'done' keyword is missing

D The test command syntax is incorrect

💡 Hint

Check if the loop changes the variable controlling the condition.

Since 'count' is never increased, the condition never becomes true, so the loop never stops.

🚀 Application

advanced

Using until loop to wait for a file

Which script waits until a file named 'ready.txt' exists, then prints 'File is ready'?

A

while [ ! -f ready.txt ]; do sleep 1; done
echo "File is ready"

B

until [ ! -f ready.txt ]; do sleep 1; done
echo "File is ready"

C

while [ -f ready.txt ]; do sleep 1; done
echo "File is ready"

D

until [ -f ready.txt ]; do sleep 1; done
echo "File is ready"

💡 Hint

The until loop runs while the condition is false, so it waits until the file exists.

Option D waits until the file exists (-f ready.txt is true), then exits the loop and prints the message.

🧠 Conceptual

expert

Behavior of until loop with command exit status

What does this script print? count=1 until ping -c1 -W1 8.8.8.8 >/dev/null 2>&1 echo "Attempt $count failed" ((count++)) done echo "Ping successful after $count attempts"

A Infinite loop without any output

B Prints success message immediately without any attempts

C Prints 'Attempt 1 failed' repeatedly until ping succeeds, then prints success message with count

D Runs once and prints 'Attempt 1 failed' then exits without success message

💡 Hint

The until loop runs while the command returns failure (non-zero exit).

The loop repeats ping attempts until it succeeds. Each failure prints a message and increments count. When ping succeeds, loop ends and success message prints.