How can grep be used to narrow down the results of 'apropos'?

You can use grep in combination with apropos to filter the results based on specific keywords. Here’s how you can do it:

Basic Usage: You can pipe the output of apropos to grep to search for specific terms. For example, if you want to find commands related to "file", you can use:
```
apropos . | grep file
```
Case Insensitive Search: If you want to ignore case sensitivity, you can use the -i option with grep:
```
apropos . | grep -i file
```
Multiple Keywords: To search for multiple keywords, you can use the -E option for extended regex:
```
apropos . | grep -E 'file|directory'
```
Count Matches: If you want to count how many matches there are, you can add the -c option:
```
apropos . | grep -c file
```

These commands will help you narrow down the results of apropos to find exactly what you're looking for.