Get the count of IPs from log file in Linux

awk '{print $1}' apache.log |sort -n | uniq -c |sort -nr | head

1. Get the IPs from first field of apache.log
2. Sort the IPs to process it further
3. Get the count of each IP
4. Sort the IPs based on count

Using regular expression:

grep -E -o "([0-9]{1,3}[\.]){3}[0-9]{1,3}" apache.log |sort -n| uniq -c | sort -nr | head