Counting IP Addresses in a Log File

I've been using grep to search through files on linux / mac for years, but one flag I didn't use much until recently is the -o flag. This tells grep to only output the matched pattern (instead of lines that mach the pattern).

This feature turns out to be pretty handy, let's say you want to find all the IP addresses in a file. You just need to come up with a regular expression to match an IP, I'll use this: "[0-9]\+\.[0-9]\+\.[0-9]\+\.[0-9]\+" it's not perfect, but it will work.

grep -o "[0-9]\+\.[0-9]\+\.[0-9]\+\.[0-9]\+" httpd.log

How can I find unique ip addresses in a log file?

We can use the uniq command to remove duplicate ip addresses, but uniq needs a sorted input. We can do that with the sort command, like so:

grep -o "[0-9]\+\.[0-9]\+\.[0-9]\+\.[0-9]\+" httpd.log | sort | uniq

Show me the number of times each IP shows up in the log

Now we can use the -c flag for uniq to display counts:

grep -o "[0-9]\+\.[0-9]\+\.[0-9]\+\.[0-9]\+" httpd.log | sort | uniq -c

This will output something like:

    7 10.0.0.30
    1 10.0.0.80
    3 10.0.0.70

The ip counts are not in order, so we can pass our results through sort again, this time with the -n flag to use a numeric sort.

grep -o "[0-9]\+\.[0-9]\+\.[0-9]\+\.[0-9]\+" httpd.log | sort | uniq -c | sort -n

The above will put them in order from least to greatest, you can pipe the result to tail if you only want to see the top N IP addresses!

Pretty handy right? It works great for counting or finding ip addresses in nginx, apache or any kind of log files with ip addresses.

Other regex patterns to match an IP address

As I mentioned the pattern we are using above is not perfect, but it works pretty well and is reasonably easy to understand. Here are a few regular expressions that can be used to match IP addresses in a log file (note I have taken out some of the escaping):

• [0-9]+\.[0-9]+\.[0-9]+\.[0-9]+ - this is the one used above, the shortfall is that it can match more than 3 numbers in each octet position. We will improve the pattern in the next one.
• [0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3} - this improves the accuracy because each octet is now 1-3 digits, but is a bit long and still not perfect as it can match 999.999.999.999 which is not valid.
• [0-9.]+ - short simple regex, but will end up matching all kinds of numbers and not just ips.
• [0-9.]{6,15} - a simple and short pattern, takes advantage the length of the IP being between 6 and 15 characters.

If you want an even more accurate regex pattern to match an ip address, it gets quite complex and lengthy. You have to account for the fact that the max number is 255 in each octet position. This means using or | statements within the pattern, it gets quite long so if your log file is not getting any false positives you might just stick to a simpler pattern.