Running commands in background (&) in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this background command?

Consider the following bash command run in a terminal:

sleep 2 & echo "Done"

What will be printed immediately after running this command?

Bash Scripting

sleep 2 & echo "Done"

A Done

B No output until 2 seconds pass

C Done\nsleep 2

D sleep: command not found

💡 Hint

The ampersand (&) runs the first command in the background, so the next command runs immediately.

The command 'sleep 2 &' runs sleep in the background, so the shell immediately runs 'echo "Done"' which prints 'Done'.

💻 Command Output

intermediate

What happens if you run multiple background commands?

What will be the output of this script?

echo Start
sleep 1 &
sleep 2 &
echo End

Choose the correct output order.

Bash Scripting

echo Start
sleep 1 &
sleep 2 &
echo End

A Start\nEnd\n(sleep 1 and sleep 2 outputs)

B Start\nEnd

C Start\nsleep 1\nsleep 2\nEnd

D End\nStart

💡 Hint

Background commands do not produce output unless they have their own output commands.

Only 'echo' commands produce output here. 'sleep' commands run silently in background. So output is 'Start' then 'End'.

🔧 Debug

advanced

Why does this background command fail to run?

Look at this command:

my_script.sh &

It gives an error: 'my_script.sh: command not found'. Why?

Bash Scripting

my_script.sh &

A Background commands cannot run scripts

B The ampersand (&) is misplaced and causes syntax error

C The script is not executable or not in PATH

D The shell does not support background commands

💡 Hint

Check if the script file has execute permission and is in the current directory or PATH.

The error means the shell cannot find 'my_script.sh' as a command. Usually because it's not executable or not in PATH.

🚀 Application

advanced

How to run a command in background and save its output to a file?

You want to run long_task.sh in background and save its output to output.log. Which command does this correctly?

A long_task.sh & > output.log

B long_task.sh & output.log >

C long_task.sh &> output.log &

D long_task.sh > output.log &

💡 Hint

Redirect output before the ampersand to capture it.

Redirecting output with > before & sends output to file while running command in background.

🧠 Conceptual

expert

What is the effect of running a pipeline with background (&)?

Consider this command:

cat file.txt | grep 'hello' &

What happens when you run it?

A The whole pipeline runs in background, output goes to terminal

B Only 'grep' runs in background, 'cat' runs in foreground

C Syntax error because & cannot be used with pipelines

D The pipeline runs in background, output is discarded

💡 Hint

The ampersand puts the entire pipeline in background.

The & at the end runs the entire pipeline in background. Output still goes to terminal unless redirected.