When would you use the -v option in the grep command?

The -v option in the grep command is used to invert the match. This means that instead of displaying lines that match the specified pattern, it will display lines that do not match the pattern. You would use the -v option in the following scenarios:

Filtering Out Unwanted Lines: When you want to exclude certain lines from the output. For example, if you want to see all lines in a file except those that contain a specific word.
```
grep -v "unwanted_word" filename.txt
```
Finding Non-Matching Patterns: When you need to identify lines that do not conform to a certain pattern, which can be useful for data validation or cleaning.
Combining with Other Options: The -v option can be combined with other options, such as -i for case-insensitive matching or -r for recursive searches, to refine the output further.

Using the -v option is helpful when you want to focus on the absence of certain data in your search results.