Access logfiles from a web server need to be filtered before the data is passed on to gnuplot. Listing 5, the Perl script that was used in the previous article, can be used in this one as well. Each line in the access logfile produces one line of output; of the many items in a line of the access logfile, four items are extracted: the timestamp, URL, IP address, and status code of the request. The URL in the output is not the actual URL but its rank in the list of URLs in the file. Similarly, the IP address is the rank of the actual IP address in a sorted list. Both of these are integer numbers. The output file so created can be read directly by gnuplot, as you will see later in this article.

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