📘 ** 0 Exit Status Code in Bash**

---

---

🎯 What You Will Learn

1. Understand what the **exit status code **0 represents in Bash.
2. Learn how Bash interprets success or failure based on exit codes.
3. Detect and verify exit code 0 using $? and logical operators.
4. Apply exit code 0 effectively in WordPress VPS scripts for automation.
5. Identify when 0 is returned, how to test it, and how to use it in flow control.

---

1. 5W + 1H Framework

Element	Description
What	Exit status 0 is a numeric signal that a command or script completed successfully.
Why	It lets Bash (and you) decide whether to continue, stop, or perform another action automatically.
Who	Bash users, WordPress VPS administrators, and DevOps engineers.
When	Every time a command or script completes execution.
Where	Stored in the special variable $?.
How	Bash automatically sets $?=0 if a command finishes without errors.

---

2. Concept Overview

In Bash, every command that executes returns an exit status code. This code tells the shell whether the command ran successfully or failed.

• 0 → Success (command completed without errors)
• Non-zero (1–255) → Failure (some form of error occurred) In logic:
• 0** is “true”** (success condition)
• Non-zero is “false” (failure condition)

Bash treats exit code 0 as a green light for continuing a script or chain.

---

3. Core Syntax and Examples

1️⃣ Check Exit Code of a Command

ls /var/www/html
echo $?

If the directory exists, $? prints 0. If it doesn’t exist, you’ll get a non-zero value like 2.

2️⃣ Use $? to Verify Success

ping -c1 google.com > /dev/null
if [ $? -eq 0 ]; then
  echo "Network connection is active."
else
  echo "Network check failed."
fi

When ping succeeds, exit code is 0 and the message confirms success.

3️⃣ Using true Command for Testing

true
echo $?

true is a built-in Bash command that always returns ****0, useful for testing script logic.

4️⃣ Chain Commands with &&

wp plugin update --all && echo "✅ All plugins updated successfully!"

The message prints only if the previous command exits with 0. If any error occurs, it skips the second command.

5️⃣ Manual Success Return

#!/bin/bash
echo "Script executed correctly."
exit 0

Here, exit 0 explicitly tells Bash that the script ended without errors.

6️⃣ Combined Conditional Example

tar -czf /root/backup.tar.gz /var/www/html
if [ $? -eq 0 ]; then
  echo "Backup created successfully."
else
  echo "Backup failed!"
fi

tar exits 0 if the archive was created properly. Any issue (e.g., missing path) would produce a non-zero code.

4. Expected Output Demonstration

Command	Output	Exit Code	Meaning
ls /var/www/html; echo $?	0	0	Directory exists → success
ping -c1 google.com > /dev/null; echo $?	0	0	Network reachable
true; echo $?	0	0	Always successful
wp core is-installed --path=/var/www/html; echo $?	0	0	WordPress installation detected

---

5. WordPress & VPS Use Cases

Scenario	Example Command	Expected Result
Core update check	wp core update && echo "WordPress updated successfully"	Confirmation message appears only when exit code is 0.
Backup verification	tar -czf /backup/site.tar.gz /var/www/html && echo "Backup OK"	Prints “Backup OK” if no errors occur.
Network validation before sync	ping -c1 wpstrategist.com >/dev/null && rsync -av /data remote:/backup	rsync only runs when ping returns 0.
Service restart sequence	systemctl restart redis && echo "Redis restarted cleanly"	Prints success message when restart worked.

---

6. Conditional Logic Behavior

Bash operators use 0 as their logic base:

• && → Execute next command if previous exited 0
• || → Execute next command if previous exited non-zero
• if → Condition passes if exit code = 0 Example:

if wp core is-installed; then
  echo "WordPress detected."
fi

if executes the block only if wp core is-installed returns 0.

7. Inside a Script

#!/bin/bash
wp core is-installed --path=/var/www/html

if [ $? -eq 0 ]; then
  echo "✅ WordPress detected"
  exit 0
else
  echo "❌ WordPress not installed"
  exit 1
fi

Expected Behavior

• If installed → prints “✅ WordPress detected” and exits 0
• If not installed → prints “❌ WordPress not installed” and exits 1

---

8. Testing & Validation

Test different return cases interactively:

true; echo $?          # → 0
ls /var/www/html; echo $?   # → 0 if exists
wp help >/dev/null; echo $? # → 0 if wp-cli works

Each command that runs without failure will produce an exit code of 0.

9. Best Practices

• **Always check **$? after critical operations (e.g., backups, updates).
• Use exit 0 explicitly at the end of scripts to mark success.
• For reliability, combine with conditional logic like && or if.
• When automating WordPress tasks via cron, log both output and $?.
• Treat “silence” carefully — some commands produce no output but still fail; rely on $? for certainty.

---

10. Troubleshooting Notes

Symptom	Explanation	Solution
Script always returns 0	Some commands succeed even when output looks empty.	Use explicit checks and logs.
Conditional always passes	Comparison operator mistake (= instead of -eq).	Use [ $? -eq 0 ].
Automation proceeds even after failure	Missing set -e or not checking $?.	Add set -e or manual condition validation.

---

11. Quick Lab

Task

Write a script that checks if /var/www/html/wp-config.php exists, and prints a success message only when exit code is 0.

Script

#!/bin/bash
ls /var/www/html/wp-config.php >/dev/null 2>&1
if [ $? -eq 0 ]; then
  echo "✅ WordPress configuration detected."
  exit 0
else
  echo "❌ Configuration file missing."
  exit 1
fi

Expected Result

• If file exists → ✅ WordPress configuration detected.
• If not → ❌ Configuration file missing. Run:

echo $?

→ will return 0 if successful, 1 if not.

12. Cheat Sheet

Command	Description
echo $?	Show exit status of last command
exit 0	End script successfully
true	Always return exit code 0
command && next	Execute next command only on success
if [ $? -eq 0 ]	Check if last command succeeded

---

13. Summary

• Exit code 0 is the universal indicator of success in Bash.
• $? stores this value after each command.
• 0 acts as “true” in conditionals (if, &&).
• Proper use of 0 improves automation reliability and script stability.
• Always verify exit codes — never assume success from silence.

---