set -e for exit on error in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does set -e do in a bash script?

set -e makes the script stop running immediately if any command returns an error (non-zero exit code).

beginner

Why is set -e useful in bash scripts?

It helps catch errors early by stopping the script, so you don't run commands that depend on failed steps.

beginner

How do you enable set -e in a bash script?

Add set -e near the top of your script, usually after the #!/bin/bash line.

beginner

What happens if a command fails after set -e is set?

The script immediately exits and does not run any more commands.

intermediate

Can set -e be turned off in the middle of a script?

Yes, by running set +e you can disable the exit-on-error behavior.

What does set -e do in a bash script?

A Ignores errors and continues running

B Stops the script if any command fails

C Prints all commands before running them

D Runs the script in debug mode

set -e causes the script to exit immediately if any command returns a non-zero exit code (an error).

Where should you place set -e in your bash script?

A At the very end of the script

B Anywhere in the script, it doesn't matter

C Only inside functions

D Near the top, after the shebang line

Placing set -e near the top ensures the script stops on errors from the start.

How do you disable the exit-on-error behavior after enabling set -e?

A exit 0

B set -x

C set +e

D unset -e

set +e disables the exit-on-error behavior.

If a command fails after set -e is set, what happens?

A The script exits immediately

B The script pauses and waits for user input

C The script continues running

D The command is retried automatically

The script exits immediately to avoid running commands that depend on the failed one.

Which of these is a good reason to use set -e?

A To catch errors early and avoid unexpected results

B To ignore errors and keep going

C To print all commands before running

D To make scripts run faster

set -e helps catch errors early by stopping the script when something goes wrong.

Explain what set -e does in a bash script and why it is helpful.

Think about how scripts behave when a command fails.

Describe how to enable and disable the exit-on-error behavior in a bash script.

Remember the commands start with 'set' and use plus or minus.

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