Day 21/ 30 Days of Linux Mastery: 'diff' Command

[Lomanu4]

Table of Contents

• Introduction
• What is the diff Command?
• Core diff Commands
• Real-World Scenario: diff Command
• Conclusion
• Let's Connect

Introduction


Welcome back to Day 21 of this practical Linux challenge! Today, we are diving into one of the most useful Linux commands: diff.

Knowing how to compare files is a core skill that shows attention to detail and debugging awareness.


What is the diff Command?


The diff command helps you compare the contents of two files line by line. It’s essential for:

• Verifying configuration changes
• Reviewing file versions
• Debugging or troubleshooting mismatches
• Pre-deployment audits

This is especially useful in production environments where systems grow large and messy fast.


Core diff Commands


Basic Syntax for diff is


diff [options] file1 file2

More commonly used diff commands options are listed in the table below.

diff Options	Description
-y	Displays output side by side
-c	Produces a context diff (shows surrounding lines)
-u	Unified diff format (commonly used for patches)
--color	Adds color to differences in output
-r	Recursively compares directories
--suppress-common-lines	Used with -y, hides lines that are the same

Real-World Scenario: diff Command

• We will create a file, then copy it as a backup and modify it by adding more words inside.

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• Compare the files using diff

diff demologs.txt demologsbackup.txt

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• Let's use side-by-side comparison to view the files easily

diff -y demologs.txt demologsbackup.txt

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you can see the last line that was included.

• Use Unified Format for Patching

diff -u demologs.txt demologsbackup.txt > patch.diff

This creates a .diff file that can be used to patch another demolog file using patch. Shows you the modification and versions of both files.

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Conclusion


Whenever you need to check a file and compare with older versions to see changes or modifications, always think of using the diff command!

The diff command is not flashy, but it is one of those must-know tools that gets real work done. Whether you are reviewing configs, debugging a deployment, or managing drift in production, diff helps you stay in control.

If this is helpful to you, feel free to bookmark, comment, like and follow me for Day 22!


Let's Connect!


If you want to connect or share your journey, feel free to reach out on

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I am always happy to learn and build with others in the tech space.

#30DaysLinuxChallenge #Redhat#RHCSA #RHCE #CloudWhistler #Linux #Rhel #Ansible #Vim #CloudComputing #DevOps #LinuxAutomation #IaC #SysAdmin#CloudEngineer

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