From: Michael Malone <michael.malone@...>
Date: 2009-03-25T05:22:26+09:00
Subject: Re: problem with gsub! in file


>> I am new to Ruby and trying to do a find and replace on a text file
>> based on a regular expression.  When I step through the code line by
>> line, it appears that the appropriate line in the file is changed, but
>> when I exit the function, the file hasn't been modified.  Are in-place
>> edits of files allowed? can you see what it wrong here?
>>
>> Here is the body of the function:
>>
>> def ReplaceGuid(guid)
>>         r = nil
>>         sconfProj = File.open("myfile.vcproj", "r+").each do |line|
>>                 m = @guidExp.match(line)
>>                 if !m.nil?
>>                         str = m[1]
>>                         r = %r{#{str}}
>>                         line.gsub!(r, guid)
>>                         break
>>                 end
>>         end
>> end
>>
>> Many thanks,
>> Jen
>>     
The problem is this: you're reading the contents of your file into 
memory, changing the copy in memory and expecting it to propagate to the 
physical file.  Try this: (though I haven't tested or run it, so there 
might be some errors)

def ReplaceGuid(guid)
   outfile = File.new("Some_filename", 'w')
   found_match = false
   IO.read("myfile.vcproj").each_line do |line|
      if (@guidExp =~ (line)) && !found_match
         line.gsub!($1, guid)
         found_match = true
      end
      outfile.puts line
   end
   outfile.close
end

That reads in the original and writes the output to a new file.  I'm assuming you wanted to stop at the first match, which is what would happen in your original code.

HTH,
Michael


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