set -e for exit on error in Bash Scripting - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to make the script exit immediately if any command fails.

Bash Scripting

#!/bin/bash
[1]
echo "Start script"
false
echo "This will not print if exit on error is set"

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

Aset -e

Bexit 1

Cset +e

Dtrap 'exit' ERR

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'set +e' which disables exit on error.

Using 'exit 1' without condition, which exits immediately.

Using 'trap' incorrectly without understanding its purpose.

Using 'set -e' makes the script stop running if any command returns an error.

2fill in blank

medium

Complete the code to enable exit on error and print a message before exiting.

Bash Scripting

#!/bin/bash
set -e
trap 'echo "Error occurred, exiting."' [1]
echo "Running script"
false
echo "This will not print"

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

AEXIT

BERR

CTERM

DINT

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'EXIT' which triggers on any exit, not just errors.

Using 'INT' or 'TERM' which are signals for interrupts or termination.

The 'ERR' trap runs when a command fails, allowing a message before exit.

3fill in blank

hard

Fix the error in the script to ensure it exits on any command failure.

Bash Scripting

#!/bin/bash
[1]
echo "Start"
false
echo "End"

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

Aset +e

Bset -x

Cset -e

Dset -u

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'set +e' which disables exit on error.

Using 'set -u' which treats unset variables as errors but doesn't exit on command failure.

'set -e' ensures the script exits immediately on any command failure.

4fill in blank

hard

Fill both blanks to create a script that exits on error and prints a custom message on failure.

Bash Scripting

#!/bin/bash
[1]
trap '[2] "Script failed."' ERR
echo "Running"
false
echo "Done"

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

Aset -e

Becho

Cexit

Dset +e

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'set +e' disables exit on error.

Using 'exit' in trap without message.

Using wrong commands in trap.

'set -e' enables exit on error, and 'echo' prints the message when trap triggers.

5fill in blank

hard

Fill all three blanks to create a script that exits on error, prints a message on error, and disables exit on error after a command.

Bash Scripting

#!/bin/bash
[1]
trap '[2] "Error detected."' ERR
echo "Start"
set [3]
false
echo "This will print because exit on error is disabled"

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

Aset -e

Becho

C-x

D+e

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'set +e' too early disables exit on error.

Using wrong trap commands.

Confusing '+e' and '-e' options.

'set -e' enables exit on error, 'echo' prints the message on error, and 'set +e' disables exit on error.

Practice

1. What does the set -e command do in a bash script?

easy

A. It stops the script immediately if any command returns a non-zero exit status.

B. It prints all commands before executing them.

C. It ignores errors and continues running the script.

D. It runs the script in debug mode.

Solution

1. Step 1: Understand the purpose of set -e

   The set -e option tells bash to exit the script if any command fails (returns a non-zero status).

2. Step 2: Compare with other options

   Options like printing commands or ignoring errors do not match set -e's behavior.

3. Final Answer:

   It stops the script immediately if any command returns a non-zero exit status. -> Option A

4. Quick Check:

   set -e = exit on error [OK]

Hint: Remember: set -e means exit on any error [OK]

Common Mistakes:

• Confusing set -e with set -x (debug mode)
• Thinking it ignores errors instead of stopping
• Assuming it prints commands before running

2. Which of the following is the correct way to enable exit on error in a bash script?

easy

A. set -e

B. set +e

C. exit -e

D. enable -e

Solution

1. Step 1: Recall the syntax for enabling exit on error

   The correct syntax to enable exit on error is set -e.

2. Step 2: Eliminate incorrect options

   set +e disables exit on error, exit -e and enable -e are invalid commands.

3. Final Answer:

   set -e -> Option A

4. Quick Check:

   Enable exit on error = set -e [OK]

Hint: Use set -e to turn on exit on error [OK]

Common Mistakes:

• Using set +e which disables exit on error
• Confusing exit command with set
• Typing invalid commands like enable -e

3. Consider this script with set -e enabled:

#!/bin/bash
set -e
echo "Start"
false
echo "End"

What will be the output when this script runs?

medium

A. Start
End

B. No output

C. End

D. Start

Solution

1. Step 1: Analyze script commands with set -e

   The script prints "Start", then runs false which returns a non-zero exit status causing the script to exit immediately.

2. Step 2: Determine which commands run

   Because of set -e, the script stops after false, so "End" is never printed.

3. Final Answer:

   Start -> Option D

4. Quick Check:

   set -e stops script on error, so only "Start" prints [OK]

Hint: Script stops at first error, so later lines don't run [OK]

Common Mistakes:

• Expecting all echo statements to run
• Ignoring that false returns error
• Thinking set -e allows script to continue

4. You have this script:

#!/bin/bash
set -e
echo "Start"
ls /nonexistent_directory
echo "End"

The script exits immediately after the ls command. How can you fix it to continue even if ls fails?

medium

A. Remove set -e from the script.

B. Add || true after the ls command.

C. Change ls to ls -e.

D. Add set +e at the start of the script.

Solution

1. Step 1: Understand why script exits

   set -e causes the script to exit on any command failure, so ls /nonexistent_directory failing stops the script.

2. Step 2: Use || true to ignore error

   Appending || true makes the command always succeed, preventing exit.

3. Final Answer:

   Add || true after the ls command. -> Option B

4. Quick Check:

   Use command || true to bypass set -e exit [OK]

Hint: Add || true to ignore errors on specific commands [OK]

Common Mistakes:

• Removing set -e loses error protection
• Using invalid ls -e option
• Trying set +e disables exit globally, not selective

5. You want a bash script to stop on any error except for a specific command that might fail but should not stop the script. How do you write this script snippet correctly?

#!/bin/bash
set -e
# Your command here
other_command

Which snippet correctly allows your_command to fail without stopping the script?

hard

A. your_command ; true
other_command

B. set +e
your_command
other_command

C. your_command || true
other_command

D. trap '' ERR
your_command
other_command

Solution

1. Step 1: Understand selective error ignoring

   To allow one command to fail without stopping the script under set -e, append || true to that command.

2. Step 2: Compare other options

   your_command ; true other_command: your_command ; true fails because set -e exits after your_command before true. set +e your_command other_command disables set -e but doesn't re-enable it for other_command. trap '' ERR your_command other_command ignores ERR trap but doesn't restore it, affecting other_command.

3. Final Answer:

   your_command || true other_command -> Option C

4. Quick Check:

   Use command || true to ignore errors selectively [OK]

Hint: Add || true after command to ignore its errors [OK]

Common Mistakes:

• Disabling set -e globally instead of locally
• Using if without handling exit status properly
• Using traps unnecessarily complicates script