Problem with gsub! in file

ruby-talk
1

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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