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Log file analysis
Input / Output example from a Well House Consultants training course
More on Input / Output [link]

This example is described in the following article(s):
   • Lua examples - coroutines, error handling, objects, etc - [link]

Source code: loganal Module: U110
--[[

Reads a web access log file ... breaking each line down into a
series of space separated fields in a table.

In this example, all that we have done with the data is then to
identify and count the number of unique values in the first column;
with the web server log file we used, this means that we counted
the number of times each different client called up a page.

]]


fh,err = io.open("../mx/data/access_log.xyz")
if err ~= nil then
        print (err)
        return
        end
lynes = 0
all = {}
counters = {}

while true do
        stuff = fh.read(fh)
        if stuff == nil then break end
        lynetab = {}
        for i in string.gmatch(stuff,"(%S+)") do
                lynetab[#lynetab+1] = i
                -- print (i)
                end
        all[#all+1] = lynetab
        host = lynetab[1]
        if counters[host] == nil then counters[host] = 0 end
        counters[host] = counters[host] + 1
        -- print (stuff)
        lynes = lynes + 1
end
print ("There are",lynes,"lines")

-- Output a table of the visiting clients, and the hit count for each

for k,v in pairs(counters) do
        print (string.format("%-10s %4d",k,v))
        end

-- Now output the same list again, but sorted.

-- You need to make up an indexed table of the keys

ktab = {}
for k,_ in pairs(counters) do
        ktab[#ktab+1] = k
        end

-- and define how the records are to be compared (unless
-- you want a default sort of the keys)

function myway(x,y)
        if counters[x] < counters[y] then return true end
        return false
end

table.sort(ktab,myway)

for _,v in ipairs(ktab) do
        print (string.format("%-10s %4d",v,counters[v]))
        end

--[[ Sample output ------------------------------------

[trainee@easterton nts]$ lua loganal
There are 6912 lines
dolphin 11
magnet 312
mussel 232
tuna 61
aviemore 318
plaice 61
lecht 26
whale 1044
localhost 1
whiting 2
whelk 1
manatee 1
dab 1
seaweed 4
Wed 1
dogfish 22
walrus 310
o_whelk 458
seal 313
trout 302
skate 1995
perch 391
clam 45
catfish 5
pilchard 1
sardine 348
flipper 322
sealion 324
localhost 1
manatee 1
whelk 1
Wed 1
dab 1
pilchard 1
whiting 2
seaweed 4
catfish 5
dolphin 11
dogfish 22
lecht 26
clam 45
tuna 61
plaice 61
mussel 232
trout 302
walrus 310
magnet 312
seal 313
aviemore 318
flipper 322
sealion 324
sardine 348
perch 391
o_whelk 458
whale 1044
skate 1995
[trainee@easterton nts]$

]]


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
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