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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
                        emails[fulladdy] = 1

-- 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})

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")
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

Books covering this topic
Yes. We have over 700 books in our library. Books covering Lua are listed here and when you've selected a relevant book we'll link you on to Amazon to order.

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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The Horse's mouth provides a daily tip or thought.
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• And there's a global index here.

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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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