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Looking for (and counting) email addresses in a log file
Input / Output example from a Well House Consultants training course
More on Input / Output [link]

This example is described in the following article(s):
   • New Lua Examples - for last weeks delegates - [link]

Source code: emmas Module: U110
--[[
This example looks for all the email addresses in a web server
log file. You might not expect there to be any email addresses
in such a file, but in practise, web crawlers and other automata
often include an email address in their user agent string as a
courtesy to the web server admin (this is not universal - many
provide a more useful URL instead to explain why they're crawling
you. ]]


flow = io.open("../data/ac_20090727","r")
emails = {}
while true do
        line = flow:read()
        if not line then break end

        -- look for all email addresses in the log file line
        -- if there are none, the loop will be skipped
        for name,domain in string.gmatch(line,"([-%a%d%._]+)@([-%a%d.]+)") do

                -- Really no need to split and rejoin the email address
                -- it was a part of the demonstration.
                fulladdy = name .. "@" .. domain

                -- Count up the number of times each address occured

                if emails[fulladdy] then
                        emails[fulladdy] = emails[fulladdy] + 1
                else
                        emails[fulladdy] = 1
                end
        end
end

-- Turn a non-indexed table (a hash) into an indexed one for sorting

mypairs = {}
for name,value in pairs(emails) do
    table.insert(mypairs,{name=name, value=value})
    end

table.sort(mypairs,function(a,b) return a.value < b.value end)

for k,v in pairs(mypairs) do
        io.write (v.value .. " -- " .. v.name .. "\n")
        end
Learn about this subject
This module and example are covered on the following public courses:
 * Learning to program in Lua
 * Lua Programming
 * Lua Programming
Also available on on site courses for larger groups

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Other Examples
This example comes from our "Input / Output" training module. You'll find a description of the topic and some other closely related examples on the "Input / Output" module index page.

Full description of the source code
You can learn more about this example on the training courses listed on this page, on which you'll be given a full set of training notes.

Many other training modules are available for download (for limited use) from our download centre under an Open Training Notes License.

Other resources
• Our Solutions centre provides a number of longer technical articles.
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This is a sample program, class demonstration or answer from a training course. It's main purpose is to provide an after-course service to customers who have attended our public private or on site courses, but the examples are made generally available under conditions described below.

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