Shell options (set -e, set -x) in Linux CLI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the shell option set -e do in a script?

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

beginner

What is the purpose of set -x in a shell script?

set -x turns on debugging mode. It shows each command and its arguments as they run, so you can see what the script is doing step-by-step.

beginner

How can set -e help in real-life scripting?

It stops the script when something goes wrong, like a missing file or failed command. This prevents errors from causing bigger problems later.

intermediate

How do you turn off the effects of set -x in a script?

You use set +x to stop showing commands as they run. This is useful to reduce clutter after debugging.

intermediate

What happens if you run a script with set -e and a command fails inside a loop?

The script will stop immediately at the failed command, even inside loops, unless you handle errors explicitly.

What does set -e do in a shell script?

A Runs the script in the background

B Shows each command before running it

C Ignores errors and continues

D Stops the script if any command fails

set -e stops the script immediately if any command returns an error.

Which option shows commands as they run for debugging?

A set -e

B set -x

C set +e

D set +x

set -x enables debugging by printing commands before execution.

How do you disable the debugging mode started by set -x?

A set +x

B set -n

C set -e

D set +e

set +x turns off the debugging mode.

If a command fails inside a loop with set -e, what happens?

A The script ignores the error and continues

B The loop skips the failed command and continues

C The script stops immediately

D The loop restarts from the beginning

set -e causes the script to stop immediately on any command failure, even inside loops.

Why would you use set -e in a script?

A To stop on errors and avoid unexpected results

B To speed up the script

C To debug commands

D To run commands silently

set -e helps catch errors early by stopping the script when a command fails.

Explain what set -e and set -x do in a shell script and why they are useful.

Think about error handling and debugging.

Describe a situation where using set -e would prevent a problem in a script.

Imagine a script copying files or installing software.

Practice

1. What does the shell option set -e do in a script?

easy

A. Stops the script immediately if any command returns an error

B. Prints each command before executing it

C. Ignores all errors and continues running

D. Runs the script in the background

Solution

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

   This option makes the shell stop running the script if any command fails (returns a non-zero exit code).

2. Step 2: Compare with other options

   set -x prints commands, but set -e stops on errors, so stopping on error is correct.

3. Final Answer:

   Stops the script immediately if any command returns an error -> Option A

4. Quick Check:

   set -e stops on error [OK]

Hint: Remember: 'e' for error stop [OK]

Common Mistakes:

• Confusing set -e with set -x
• Thinking it ignores errors
• Assuming it runs commands silently

2. Which of the following is the correct way to enable both set -e and set -x in a shell script?

easy

A. set -x e

B. set -xe

C. set e -x

D. set -e x

Solution

1. Step 1: Understand combined options syntax

   Shell options can be combined after a single dash, order does not matter, so set -xe works.

2. Step 2: Check options with spaces

   set e -x is invalid syntax, and set -x e or set -e x set only one option.

3. Final Answer:

   set -xe -> Option B

4. Quick Check:

   Combine options after one dash [OK]

Hint: Combine flags after one dash, order doesn't matter [OK]

Common Mistakes:

• Using spaces between flags incorrectly
• Writing flags without dashes
• Assuming order matters

3. Given this script snippet with set -e enabled:

set -e
mkdir /tmp/mydir
cd /tmp/mydir
false
echo "This will not print"

What will be the output when running this script?

medium

A. Fails at mkdir and stops immediately

B. Creates directory, changes directory, prints 'This will not print'

C. Creates directory, changes directory, then stops at false; no echo output

D. Runs all commands including echo

Solution

1. Step 1: Trace commands with set -e

   The script creates /tmp/mydir, changes into it, then runs false which returns error (non-zero).

2. Step 2: Effect of set -e on error

   Because set -e stops on any error, the script stops after false and does not run the echo command.

3. Final Answer:

   Creates directory, changes directory, then stops at false; no echo output -> Option C

4. Quick Check:

   set -e stops script on error [OK]

Hint: Remember: script stops at first error with set -e [OK]

Common Mistakes:

• Assuming echo runs after error
• Thinking mkdir fails by default
• Ignoring effect of set -e

4. You have this script:

#!/bin/bash
set -x
ls /nonexistent
pwd

What is the problem and how to fix it so the script continues after the error?

medium

A. No problem; script runs all commands

B. Problem: script stops on error; fix by removing set -x

C. Problem: script prints commands; fix by removing set -x

D. Problem: script stops on error; fix by removing set -e (not set here)

Solution

1. Step 1: Analyze script options

   The script uses set -x which prints commands but does not stop on errors. There is no set -e so script continues despite ls error and runs pwd.

2. Step 2: Identify problem and fix

   Script already continues after error since no set -e. No problem exists.

3. Final Answer:

   No problem; script runs all commands -> Option A

4. Quick Check:

   set -x prints commands, set -e stops on error [OK]

Hint: Remember: set -x prints, set -e stops [OK]

Common Mistakes:

• Confusing set -x with set -e
• Assuming set -x stops script
• Ignoring missing set -e

5. You want to debug a script that sometimes fails silently. Which combination of shell options helps you see each command as it runs and stops immediately on errors?

hard

A. set -e only

B. set -x e

C. set -x only

D. set -ex

Solution

1. Step 1: Understand debugging needs

   To debug, you want to see commands as they run (set -x) and stop on errors (set -e).

2. Step 2: Combine options correctly

   set -ex enables both correctly.

3. Final Answer:

   set -ex -> Option D

4. Quick Check:

   Show commands and stop on error = set -ex [OK]

Hint: Use both -e and -x together to debug safely [OK]

Common Mistakes:

• Using only one option and missing the other
• Thinking order matters strictly
• Confusing which option stops or prints