📘 **Command Chaining using **cmd1 && cmd2

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🎯 What You Will Learn

1. Understand the concept of command chaining using && in Bash.
2. Learn how to execute multiple commands conditionally — only when the first succeeds.
3. Explore execution flow and exit status logic behind &&.
4. Apply command chaining for automation, WordPress VPS management, and system maintenance.
5. Identify and correct common mistakes when chaining commands.
6. Implement practical use cases and test them directly on your VPS.

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1. 5W + 1H Framework

Element	Description
What	&& is a logical AND operator in Bash used to chain two or more commands, where each subsequent command runs only if the previous one succeeds (exit status 0).
Why	To create reliable automation where failure in one step prevents the next from executing — e.g., avoiding corrupt deployments or partial updates.
Who	System administrators, DevOps engineers, and WordPress VPS managers.
When	When you need to execute dependent commands that should only run on success (e.g., database backups, updates, deployments).
Where	Within Bash CLI, shell scripts, or aliases for automation (like updating all plugins, restarting PHP-FPM, etc.).
How	By linking multiple commands with &&, forming a conditional execution chain. Example: cmd1 && cmd2 && cmd3

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2. Prerequisites

• Basic knowledge of:
• Bash command-line environment.
• Command exit status codes ($?).
• Understanding of the difference between sequential (;) and conditional (&&) execution.
• Access to a Linux VPS or local terminal.

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3. Core Syntax & Concept

No.	Syntax Formula	Syntax Example	Description
0	command1 && command2	apt update && apt upgrade -y	Runs command2 only if command1 exits successfully (0).
1	cmd1 && cmd2 && cmd3	cd /var/www/html && ls && echo "Listed successfully"	Chains multiple commands — each runs only if the previous succeeds.
2	(cmd1 && cmd2)	(cd /home && mkdir testdir)	Groups chained commands in a subshell.
3	cmd1 && { cmd2; cmd3; }	cd /var/www/html && { ls; pwd; }	Combines logical AND with a command group using {}.
4	cmd1 && echo "Success"	systemctl restart redis && echo "Redis restarted successfully"	Runs a message or follow-up task if the first command succeeds.
5	`cmd1 && cmd2		cmd3`

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4. Conceptual Flow

# Example 1
mkdir /root/test && echo "Directory created successfully"

Expected Output:

Directory created successfully

Explanation:

• The echo command runs only if mkdir /root/test executes without error.
• If /root/test already exists, mkdir fails → echo is skipped.

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# Example 2
cd /var/www/html && ls

Expected Output:

index.php
wp-content
wp-includes
wp-admin
...

Explanation:

• ls executes only if the directory change (cd) is successful.
• Prevents listing a directory that doesn't exist.

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# Example 3 (WordPress Automation)
wp plugin update --all && systemctl restart lsws && echo "All plugins updated and LSWS restarted"

Expected Output:

Success: Updated 12 of 12 plugins.
All plugins updated and LSWS restarted

Explanation:

• systemctl restart lsws runs only if plugin updates succeed.
• echo confirms the final completion.

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5. Use Cases in WordPress VPS

Scenario	Example Command	Description
1. Update System Packages	apt update && apt upgrade -y && apt autoremove -y	Ensures packages are updated only if the previous step succeeds.
2. Plugin & Theme Updates	wp plugin update --all && wp theme update --all	Update themes only if plugins update successfully.
3. Cache & Restart Services	redis-cli flushall && systemctl restart redis && echo "Redis cache cleared!"	Flush cache and restart service conditionally.
4. Backup & Compress Database	mysqldump -u root -p wpdb > /root/backup.sql && gzip /root/backup.sql	Compress backup only if dump creation succeeds.
5. Deployment Automation	git pull && composer install && npm run build	Ensures each build step runs only on success of the previous.
6. Safe Restart Sequence	systemctl restart php8.3-fpm && systemctl restart lsws	Avoids restarting web server if PHP fails to restart.

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6. Best Practices

Practice	Description
✅ Use && for dependent tasks only	Avoid chaining unrelated commands.
✅ Include logging	Example: cmd1 && echo "$(date): Success" >> /var/log/script.log
✅ **Combine with `
✅ Use meaningful messages	Always provide clear feedback after successful commands.
⚠️ Avoid chaining destructive commands	Never do rm -rf /var/www/html && rm -rf /home/user.
⚙️ Test interactively before automation	Always test manually before adding to cron or script.

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7. Common Mistakes & Fixes

Mistake	Example	Problem	Fix
Missing space	cmd1&&cmd2	Works but hard to read	Use cmd1 && cmd2
Wrong chaining logic	cmd1; cmd2	Runs both regardless of failure	Use && for conditional execution
Ignoring exit codes	cmd1 && cmd2	May skip cmd2 if cmd1 fails	Check $? to debug
Using sudo incorrectly	sudo cmd1 && cmd2	cmd2 may run as non-root	Apply sudo consistently where needed

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8. Troubleshooting Matrix

Issue	Cause	Solution
Second command not running	First command failed	Run echo $? to check exit status.
Unexpected behavior in script	Improper syntax or quotes	Use bash -x script.sh to debug.
Commands run even on failure	Used ; instead of &&	Replace ; with &&.
Permission denied	Insufficient privileges	Prefix with sudo or adjust file permissions.

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9. Quick Lab: Practice on VPS

Objective: Update WordPress plugins and restart OpenLiteSpeed conditionally.

wp plugin update --all --allow-root && systemctl restart lsws && echo "✅ WP Plugins updated and LSWS restarted successfully."

Expected Output:

Success: Updated 8 of 8 plugins.
✅ WP Plugins updated and LSWS restarted successfully.

Now simulate failure:

wp plugin update --path=/wrong/path && echo "Done"

Expected Output:

Error: This does not seem to be a WordPress installation.

(→ The echo is not executed.)

10. Cheat Sheet

Pattern	Meaning	Example
cmd1 && cmd2	Run cmd2 if cmd1 succeeds	ls && pwd
cmd1 && cmd2 && cmd3	Chain 3+ success-dependent commands	apt update && apt upgrade -y && reboot
cmd1 && echo "OK"	Print success message only on success	redis-cli ping && echo "Redis OK"
`cmd1 && cmd2		cmd3`

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11. Mini-Quiz

1. What happens if the first command in cmd1 && cmd2 fails? → The second command will not execute.
2. How does && differ from ;? → ; runs all commands regardless of result, while && depends on success.
3. What exit code value represents success? → 0.
4. Which chain restarts Redis only if cache flush is successful? → redis-cli flushall && systemctl restart redis.
5. What’s the output of false && echo "Run"? → Nothing — echo is skipped.

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Would you like me to continue this with cmd1 || cmd2** (logical OR chaining)** next — to complement this lesson in your Bash curriculum?