🐧 diff Command Guide (Compare Files in Linux)

The diff command is used to compare two files or directories line by line and show the differences between them. It’s widely used in development, scripting, and troubleshooting.

▶️ Basic Syntax

diff [options] file1 file2

📄 Simple Example

diff file1.txt file2.txt

Output shows:

• Lines only in file1
• Lines only in file2
• Where changes occurred

🔍 Useful Options

Side-by-side comparison

diff -y file1.txt file2.txt

Ignore whitespace

diff -w file1.txt file2.txt

Ignore case differences

diff -i file1.txt file2.txt

Show unified format (best for readability)

diff -u file1.txt file2.txt

✔ Commonly used for patches and code reviews

📂 Compare Directories

diff -r dir1 dir2

✔ Recursively compares all files

🧪 Practical Examples

Check config changes

diff -u old.conf new.conf

Compare backups

diff -r /backup1 /backup2

📌 Understanding Output

Example:

2c2
< old line
---
> new line

• c = change
• < = from first file
• > = from second file

⚡ Highlight Differences with Color

Install tools like:

• colordiff (wrapper for diff)

colordiff file1.txt file2.txt

⚠️ Common Issues

No output

✔ Files are identical

Large output

✔ Use:

diff -u file1 file2 | less

🧠 When to Use diff

• Comparing configuration files
• Reviewing code changes
• Debugging scripts
• Verifying backups

💡 Pro Tip

Use diff -u for clean, readable output—it’s the standard format used in patches and version control systems.