Parallel execution patterns in Bash Scripting - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to run two commands in parallel.

Bash Scripting

command1 & [1]

Drag options to blanks, or click blank then click option'

Acommand2 &

Bcommand2

Cwait

Dsleep 1

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting & after the second command runs it sequentially.

Using wait here pauses the script instead of running in parallel.

Adding & after command2 runs it in the background, so both commands run in parallel.

2fill in blank

medium

Complete the code to wait for all background jobs to finish.

Bash Scripting

command1 &
command2 &
[1]

Drag options to blanks, or click blank then click option'

Ajobs

Bfg

Cwait

Dkill

Attempts:

3 left

💡 Hint

Common Mistakes

Using jobs only lists jobs but does not wait.

Using fg brings a job to foreground but does not wait for all.

The wait command pauses the script until all background jobs finish.

3fill in blank

hard

Fix the error in the code to run commands in parallel and wait for them.

Bash Scripting

command1 &
command2 [1]

Drag options to blanks, or click blank then click option'

Ajobs

Bwait

Cfg

Dkill

Attempts:

3 left

💡 Hint

Common Mistakes

Not adding & after the second command runs it sequentially.

Using jobs or fg instead of wait.

The second command needs & to run in background for parallel execution. Then wait waits for all.

4fill in blank

hard

Fill both blanks to run commands in parallel and wait for them.

Bash Scripting

command1 [1]
command2 [2]
wait

Drag options to blanks, or click blank then click option'

A&

B;

C&&

D|

Attempts:

3 left

💡 Hint

Common Mistakes

Using ; or && runs commands sequentially.

Using | pipes output but does not run in background.

Adding & after both commands runs them in background. Then wait pauses until both finish.

5fill in blank

hard

Fill all three blanks to run commands in parallel, wait, and then print done.

Bash Scripting

command1 [1]
command2 [2]
[3]
echo "All done"

Drag options to blanks, or click blank then click option'

A&

Bwait

C;

D&&

Attempts:

3 left

💡 Hint

Common Mistakes

Not using & causes sequential execution.

Not using wait may print message too early.

Use & to run commands in background, then wait to pause until they finish, then print the message.

Practice

1. What does adding & at the end of a command in a bash script do?

easy

A. Runs the command in the background, allowing the script to continue immediately

B. Stops the script until the command finishes

C. Redirects the command output to a file

D. Runs the command with higher priority

Solution

1. Step 1: Understand the role of & in bash

   The & symbol placed at the end of a command tells bash to run that command in the background.

2. Step 2: Effect on script execution

   Running a command in the background means the script does not wait for it to finish and continues to the next command immediately.

3. Final Answer:

   Runs the command in the background, allowing the script to continue immediately -> Option A

4. Quick Check:

   Background execution = & at end [OK]

Hint: Remember & means run in background, no waiting [OK]

Common Mistakes:

• Thinking & pauses the script until command finishes
• Confusing & with output redirection
• Assuming & changes command priority

2. Which of the following is the correct syntax to run two commands in parallel in bash?

easy

A. command1 & command2 &

B. command1 && command2 &

C. command1 && command2

D. command1 & command2

Solution

1. Step 1: Identify how to run commands in parallel

   Appending & to a command runs it in the background. To run two commands in parallel, both must have &.

2. Step 2: Analyze options

   command1 & command2 & runs both commands with &, so both run in background simultaneously. command1 && command2 & uses && which means run second only if first succeeds, then runs second in background (but first runs in foreground). command1 && command2 uses && without background. command1 & command2 runs command1 in background but command2 in foreground, so the script blocks until command2 finishes.

3. Final Answer:

   command1 & command2 & -> Option A

4. Quick Check:

   Both commands need & to run parallel [OK]

Hint: Use & after each command to run both in parallel [OK]

Common Mistakes:

• Using && which runs commands sequentially
• Missing & on second command
• Confusing & with &&

3. What will be the output order of the following script?

echo "Start"
sleep 2 &
echo "Middle"
sleep 1 &
echo "End"
wait

medium

A. Start\nMiddle\nEnd\n(wait blocks output until sleeps finish)

B. Start\n(wait)\nMiddle\nEnd

C. Start\nMiddle\nEnd (then waits for sleeps to finish)

D. Start\nEnd\nMiddle

Solution

1. Step 1: Understand background jobs and output

   The sleep commands run in background due to &, so they do not block the script. The echo commands run immediately in order.

2. Step 2: Analyze output order

   The script prints "Start", then starts sleep 2 in background, then prints "Middle", starts sleep 1 in background, then prints "End". The wait pauses script exit until sleeps finish but does not affect output order.

3. Final Answer:

   Start\nMiddle\nEnd (then waits for sleeps to finish) -> Option C

4. Quick Check:

   Background jobs don't block echo output [OK]

Hint: Background jobs run silently; echo prints immediately [OK]

Common Mistakes:

• Assuming wait delays echo output
• Thinking sleep blocks echo
• Confusing order of background jobs

4. Identify the error in this script snippet that tries to run two commands in parallel and wait for both:

command1 &
command2
wait

medium

A. command1 & syntax is incorrect

B. wait command is missing arguments

C. Both commands run sequentially, no parallelism

D. command2 is not run in background, so wait only waits for command1

Solution

1. Step 1: Check background execution of commands

   Only command1 has & to run in background. command2 runs in foreground, blocking until it finishes.

2. Step 2: Effect on wait

   The wait command waits for all background jobs to finish. Since only command1 is background, wait waits only for it. command2 runs before wait.

3. Final Answer:

   command2 is not run in background, so wait only waits for command1 -> Option D

4. Quick Check:

   All parallel commands need & before wait [OK]

Hint: Add & to all parallel commands before wait [OK]

Common Mistakes:

• Forgetting & on second command
• Thinking wait needs arguments
• Assuming wait waits for foreground commands

5. You want to run 3 independent scripts script1.sh, script2.sh, and script3.sh in parallel and then print "All done" only after all finish. Which is the best way to do this?

hard

A. ./script1.sh && ./script2.sh && ./script3.sh && echo "All done"

B. ./script1.sh &
./script2.sh &
./script3.sh &
wait
echo "All done"

C. ./script1.sh & ./script2.sh & ./script3.sh & echo "All done"

D. ./script1.sh &
./script2.sh &
./script3.sh
echo "All done"

Solution

1. Step 1: Run all scripts in background

   Adding & after each script runs them in parallel without waiting.

2. Step 2: Use wait to pause until all finish

   The wait command pauses the script until all background jobs complete, ensuring synchronization.

3. Step 3: Print message after all finish

   After wait, echo "All done" runs, confirming all scripts finished.

4. Final Answer:

   ./script1.sh &
   ./script2.sh &
   ./script3.sh &
   wait
   echo "All done"

   -> Option B

5. Quick Check:

   Background + wait + echo after = correct pattern [OK]

Hint: Use & for parallel, then wait before next step [OK]

Common Mistakes:

• Using && runs scripts sequentially
• Missing wait causes echo to run too early
• Putting echo on same line with & causes immediate print