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catching exceptions - file handling
Exceptions. example from a Well House Consultants training course
More on Exceptions. [link]

This example is described in the following article(s):
   • Sorta sorting a hash, and what if an exception is NOT thrown - Ruby - [link]

Source code: chq Module: R111
#!/usr/bin/env ruby

def byvalue (a,b,datasource)
        return datasource[b] - datasource[a]

# catching exceptions - file handling

counter = {}
total = 0

# --------- Read whole file

        stuff = (File.new ARGV[0]).readlines

# - Action on FAILURE
        STDERR.puts("Problem was #{$!} ...")
        STDERR.puts("should we shut down nicely?")
        stuff = []
        # could exit instead

#- Action on success

        puts "Vunderbahl! we have opened our file"

# ----------

# Analysis of Data

for line in stuff
        ip = (line.split)[0]

        # create a new element in the hash if necessary
        counter[ip] = 0 unless counter[ip]
        # and count the IP addresses
        counter[ip] += 1
        total += 1

#- Ruby sorting via a sort function
#- How to sort a ruby hash by key

tops = 0
for ipv in counter.keys.sort { |a,b| byvalue a,b,counter }
        puts "#{counter[ipv]} visits from #{ipv}"
        break if ((tops += 1) > 10)
puts "Total of #{total} records analysed"


munchkin:rs grahamellis$ ./chq ac_20110907
Problem was No such file or directory - ac_20110907 ...
should we shut down nicely?
Total of 0 records analysed
munchkin:rs grahamellis$ ./chq ac_20110908
Vunderbahl! we have opened our file
12751 visits from
10968 visits from
5483 visits from
5208 visits from
5175 visits from
3546 visits from
2885 visits from
1508 visits from
1386 visits from
1295 visits from
1105 visits from
Total of 127387 records analysed
munchkin:rs grahamellis$

Learn about this subject
This module and example are covered on the following public courses:
 * Learning to program in Ruby
 * Ruby 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 Ruby 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 "Exceptions." training module. You'll find a description of the topic and some other closely related examples on the "Exceptions." 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.
• Further resources are available via the resources centre.
• All of these resources can be searched through through our search engine
• And there's a global index here.

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