Infinite loops in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an infinite loop in bash scripting?

An infinite loop is a loop that never stops running because its exit condition is never met or it has no exit condition.

beginner

How do you write a simple infinite loop using while in bash?

You can write it as:

while true; do
  # commands
 done

This runs the commands forever until you stop it.

beginner

What command can you use to stop an infinite loop running in the terminal?

Press Ctrl + C to send an interrupt signal that stops the running infinite loop.

intermediate

Why might infinite loops be useful in scripting?

They are useful for tasks that need to run continuously, like monitoring a system or waiting for events.

intermediate

Show an example of an infinite loop using for in bash.

Example:

for (( ; ; )); do
  echo "Looping forever"
  sleep 1
 done

This loops forever because there are no conditions.

Which of these is a correct way to write an infinite loop in bash?

A while true; do echo "Hi"; done

B while false; do echo "Hi"; done

C for i in 1..10; do echo "Hi"; done

D if true; then echo "Hi"; fi

Option A runs forever because 'true' is always true. Option B never runs. Option C runs once, not infinite. Option D is a single condition, not a loop.

How do you stop a running infinite loop in the terminal?

A Press Ctrl + C

B Press Ctrl + Z

C Close the terminal window

D Type 'exit' inside the loop

Ctrl + C sends an interrupt signal to stop the loop immediately. Ctrl + Z pauses the process but does not stop it.

What will this loop do?

for (( ; ; )); do echo "Hello"; done

A Print 'Hello' once

B Print 'Hello' forever

C Cause an error

D Print 'Hello' 10 times

The for loop has no conditions, so it runs forever printing 'Hello'.

Why should you be careful when writing infinite loops?

A They always run faster than normal loops

B They automatically stop after 10 minutes

C They use less memory

D They can crash your system if not controlled

Infinite loops can use up CPU and memory, causing your system to slow down or crash if not managed.

Which command inside an infinite loop can help avoid high CPU usage?

A ls

B echo "Running"

C sleep 1

D exit

Using 'sleep 1' pauses the loop for 1 second each time, reducing CPU load.

Explain what an infinite loop is and how you can create one in bash.

Think about loops that never stop running.

Describe how to safely stop an infinite loop running in your terminal and why you might want to use infinite loops.

Consider both stopping and using infinite loops.