What are common diff options?

Here are some common options for the diff command that are frequently used:

-u: Unified format output, which shows a few lines of context around the differences.
```
diff -u file1.txt file2.txt
```
-c: Context format output, providing more context around the differences than the default output.
```
diff -c file1.txt file2.txt
```
-r: Recursively compare directories and their contents.
```
diff -r dir1 dir2
```
-i: Ignore case differences in the file contents.
```
diff -i file1.txt file2.txt
```
-w: Ignore all white space when comparing lines.
```
diff -w file1.txt file2.txt
```
-q: Report only whether the files differ, without showing the actual differences.
```
diff -q file1.txt file2.txt
```
-y: Display the differences side by side.
```
diff -y file1.txt file2.txt
```
--suppress-common-lines: When used with -y, this option suppresses lines that are the same in both files.
```
diff -y --suppress-common-lines file1.txt file2.txt
```

These options can be combined to customize the output according to your needs. For example:

diff -urN dir1 dir2

This command will recursively compare dir1 and dir2, treating absent files as empty and providing a unified output format.