How to Use Exit Codes in Linux: A Comprehensive Guide

- February 02, 2025

Introduction

Exit codes in Linux are essential indicators that provide feedback on the success or failure of executed commands or scripts. Whether you're debugging a script, automating system tasks, or handling errors effectively, understanding exit codes can significantly enhance your workflow. This guide will explain what exit codes are, how to use them, and why they are crucial for scripting and automation.

What Are Exit Codes in Linux?

Understanding Exit Codes

Exit codes are numeric values returned by a process upon its termination. They help determine if a command executed successfully or encountered an error.

Why Are Exit Codes Important?

They provide feedback on command execution.
Useful for debugging scripts.
Allow automation scripts to handle failures gracefully.

Common Exit Codes and Their Meanings

Exit Code	Meaning	Description
0	Success	Command executed successfully.
1	General error	Command failed due to an unspecified reason.
2	Misuse of shell built-ins	Syntax error or invalid usage of commands.
126	Command not executable	Permission issue or incorrect execution.
127	Command not found	The specified command does not exist.
130	Terminated by Ctrl+C	Process was manually interrupted.
137	Killed by SIGKILL	Process was forcefully terminated.

How to Check Exit Codes

Checking Exit Codes of Commands

To check the exit code of a command, use:

echo $?

Example:

touch file.txt
echo $?
# Output: 0 (Success)

Using Exit Codes in Scripts

Example of a basic script utilizing exit codes:

#!/bin/bash
mkdir /root/test-folder
if [ $? -eq 0 ]; then
    echo "Directory created successfully."
else
    echo "Failed to create directory." >&2
    exit 1
fi

Advanced Use Cases of Exit Codes

Handling Multiple Exit Codes in Scripts

#!/bin/bash
echo "Checking system updates..."
sudo apt update
status=$?

if [ $status -eq 0 ]; then
    echo "Update successful."
elif [ $status -eq 100 ]; then
    echo "Updates available, please upgrade."
else
    echo "Update failed." >&2
    exit $status
fi

Using Exit Codes in Conditional Execution

mkdir /tmp/myfolder && echo "Success" || echo "Failure"

Exit Codes with Logical Operators

&& executes the second command only if the first succeeds.
|| executes the second command only if the first fails.

Example:

touch testfile && echo "File created" || echo "File creation failed"

Frequently Asked Questions (FAQs)

What happens if no exit code is specified in a script?

By default, the exit status is the last executed command’s exit code.

Can I define custom exit codes?

Yes, you can define exit codes in your scripts using exit <code>.

Example:

exit 42  # Custom exit code

How do I capture the exit code of a background process?

Use:

command &
pid=$!
wait $pid
echo $?  # Exit code of the background process

Where can I find more information on exit codes?

Refer to:

Conclusion

Exit codes play a vital role in scripting and automation within Linux. They provide feedback on process execution, helping developers debug errors and optimize their scripts. By mastering exit codes, you can write more robust and efficient scripts to manage Linux systems effectively.

By following this guide, you’ll gain the expertise needed to handle exit codes effectively in your Linux workflows. Thank you for reading the huuphan.com page!

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