The log file look like this:

examples/data/apache_access.log

127.0.0.1 - - [10/Apr/2007:10:39:11 +0300] "GET / HTTP/1.1" 500 606 "-" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
127.0.0.1 - - [10/Apr/2007:10:39:11 +0300] "GET /favicon.ico HTTP/1.1" 200 766 "-" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
139.12.0.2 - - [10/Apr/2007:10:40:54 +0300] "GET / HTTP/1.1" 500 612 "-" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
139.12.0.2 - - [10/Apr/2007:10:40:54 +0300] "GET /favicon.ico HTTP/1.1" 200 766 "-" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
127.0.0.1 - - [10/Apr/2007:10:53:10 +0300] "GET / HTTP/1.1" 500 612 "-" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
127.0.0.1 - - [10/Apr/2007:10:54:08 +0300] "GET / HTTP/1.0" 200 3700 "-" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
127.0.0.1 - - [10/Apr/2007:10:54:08 +0300] "GET /style.css HTTP/1.1" 200 614 "http://machine.local/" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
127.0.0.1 - - [10/Apr/2007:10:54:08 +0300] "GET /img/machine-round.jpg HTTP/1.1" 200 17524 "http://machine.local/" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
127.0.0.11 - - [10/Apr/2007:10:54:21 +0300] "GET /unix_sysadmin.html HTTP/1.1" 200 3880 "http://machine.local/" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
217.0.22.3 - - [10/Apr/2007:10:54:51 +0300] "GET / HTTP/1.1" 200 34 "-" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
217.0.22.3 - - [10/Apr/2007:10:54:51 +0300] "GET /favicon.ico HTTP/1.1" 200 11514 "-" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
217.0.22.3 - - [10/Apr/2007:10:54:53 +0300] "GET /cgi/machine.pl HTTP/1.1" 500 617 "http://contact.local/" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
127.0.0.1 - - [10/Apr/2007:10:54:08 +0300] "GET / HTTP/0.9" 200 3700 "-" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
217.0.22.3 - - [10/Apr/2007:10:58:27 +0300] "GET / HTTP/1.1" 200 3700 "-" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
217.0.22.3 - - [10/Apr/2007:10:58:34 +0300] "GET /unix_sysadmin.html HTTP/1.1" 200 3880 "http://machine.local/" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"
217.0.22.3 - - [10/Apr/2007:10:58:45 +0300] "GET /talks/Fundamentals/read-excel-file.html HTTP/1.1" 404 311 "http://machine.local/unix_sysadmin.html" "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.3) Gecko/20061201 Firefox/2.0.0.3 (Ubuntu-feisty)"

The Algorithm:

We need two counters, one for counting the hits from 127.0.0.1 and one to count all the other hits. Then we need to go over all the lines. Extract the IP address, and based on its value to increment one of the counters.

We expect the program to be used as ruby apache_localhost.rb data/apache_access.log. That is, we expect the user to provide the name of the Apache log file as a parameter on the command line.

Therefore in the first few lines we check if the user has supplied any filename on the command line by checking the number of elements in ARGV. If the given number of parameters is not 1, then we tell the user how to use our program and exit.

Then we copy the name of the file from ARGV to an internal variable called filename. Mostly for readability of the code.

Then we create the two counters and initialize them to 0.

The we open the file for reading and read it line-by-line using each. On each iteration the variable line will hold the current line form the file.

The IP address is the first value in every row up till the first space. There are a number of ways to extract it from the line. In this case we used the index method on the line passing a space to it. That will return the location of the first space in the line. Because the string indexing starts with 0, this number will be also the length of the IP address. Hence we have assigned the result to a variable called length.

We can use this variable then to extract the substring from the line that starts on character 0 and includes length characters. We can do that by providing the index of the beginning of the substring and the length of the substring we would like to extract. That will be the IP address from the current line.

What remains is to check if this equals to 127.0.0.1 (localhost) and increment the appropriate counter.

examples/ruby/apache_localhost.rb

if ARGV.length != 1 then
    puts "We need the name of the log file"
    exit
end

filename = ARGV[0]

local = 0
remote = 0

fh = open filename
fh.each do |line|
    length = line.index(' ')
    ip = line[0, length]
    if ip == '127.0.0.1' then
        local = local+1
    else
        remote = remote+1
    end
end

puts "Number of remote requests is #{remote}. Number of local requests was #{local}"