Well, firstly you read and print the entire file and then try to search in the remaining parts of the file (i.e nowhere). If you really want to work this way, you should seek to the beginning of the file.

Also, your $IP variable is declared inly inside the while loop. Declare it earlier (outside the loop) or print something from @IPS instead.

Also, you need another syntax for your matching:

($IP) = $line =~ /(\d+\.\d+\.\d+\.\d+)/;
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Pattern matching returns an array, and you should assign an array (anonymous array is fine) if you want to get what matched (not the count of matches = array in scalar context).