Filter IP Adresses to file

[Newbie08]

I'm a Linux newbie, so please forgive me if this is an easy question.

I need to filter (grep, awk, etc.) out all the IP addresses from /var/log/secure that attempt to access a my server to a file and sort them.

I can get the lines containing the addresses with grep and know to use sort | uniq -u to get them in order and delete duplicate entries, but I don't know how to accurately get out each IP address.

It would be possible to awk out each entry based on it's position in the string, but there must be a more accurate and more efficient way to do this.

Thanks so much for your assistance!

[anomie]

This question is common enough that some diligence on the forums / google likely would have yielded dozens of related answers.

Blunt tool approach:

# grep -o '[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}' /var/log/secure

You may need to refine that further, as it could generate false positives (e.g. 999.500.0.30 is not a real IP address).