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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/ruby

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

# catching exceptions - file handling

counter = {}
total = 0

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

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

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

#- Action on success

else
        puts "Vunderbahl! we have opened our file"
end

# ----------

# 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
end

#- 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)
end
puts "Total of #{total} records analysed"

__END__

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 83.170.93.77
10968 visits from 157.55.116.37
5483 visits from 217.160.182.81
5208 visits from 67.195.111.173
5175 visits from 66.249.72.203
3546 visits from 157.55.116.27
2885 visits from 66.249.72.76
1508 visits from 94.169.96.238
1386 visits from 67.195.37.188
1295 visits from 207.46.13.97
1105 visits from 66.249.72.111
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
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