Shell options (set -e, set -x) in Linux CLI - Commands & Configuration

Introduction

Sometimes scripts fail silently or it's hard to see what commands are running. Shell options like set -e and set -x help catch errors early and show commands as they run, making scripts easier to debug and safer to use.

When you want your script to stop immediately if any command fails to avoid unexpected results.

When you want to see each command printed before it runs to understand the script's flow.

When debugging a script that behaves unexpectedly and you need to trace its execution.

When running a critical automation where silent failures could cause bigger problems.

When learning shell scripting and you want clearer feedback on what your script does.

Commands

This command tells the shell to stop running the script immediately if any command returns a non-zero exit status. It helps prevent continuing after a failure.

Terminal

set -e

Expected Output

No output (command runs silently)

This command makes the shell print each command before it runs it. This helps you see exactly what the script is doing step-by-step.

Terminal

set -x

Expected Output

No output (command runs silently)

Runs a small script where set -e stops execution after the false command fails, so the echo command does not run.

Terminal

bash -c 'set -e; false; echo "This will not print"'

Expected Output

No output (command runs silently)

Runs a small script with set -x enabled, so each echo command is printed before its output.

Terminal

bash -c 'set -x; echo Hello; echo World'

Expected Output

+ echo Hello

Hello

+ echo World

World

Key Concept

If you remember nothing else from this pattern, remember: set -e stops your script on errors, and set -x shows each command as it runs.

Common Mistakes

Using set -e but not realizing some commands return non-zero codes even when successful.

The script may stop unexpectedly because some commands use non-zero exit codes for normal behavior.

Check command exit codes and handle exceptions or disable set -e temporarily around those commands.

Using set -x in a script with sensitive data without caution.

set -x prints all commands, which may expose passwords or secrets in logs.

Avoid set -x when handling secrets or disable it around sensitive commands.

Expecting set -e to catch errors in all cases, including commands in pipelines or subshells without extra care.

set -e does not always stop on errors inside pipelines or subshells by default.

Use set -o pipefail along with set -e to catch errors in pipelines.

Summary

Use set -e to make your script stop immediately on any error to avoid unexpected results.

Use set -x to print each command before it runs, helping you trace and debug your script.

Combine these options carefully to write safer and easier-to-understand shell scripts.

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