From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2012-06-04T23:12:04+09:00
Subject: Re: Read from several .txt files by a pattern and write the matched lines to a new file

On Mon, Jun 4, 2012 at 4:01 PM, Robert Hansen <lists@ruby-forum.com> wrote:
> Robert Hansen wrote in post #1063024:
>> $files = Array.new
>>
>> Dir.glob("**/Msg.log").entries.each { |n| $files.push(n) if
>> File.file?(n) }
>> puts "\n#{$files.size} files found\n"
>>
>> pattern = /(failed)/m
>>
>> $files.each do |element|
>>          f = File.open(element, 'r')
>>               lines = f.readlines
>>               lines.each do |line|
>>                   if line.match(pattern)
>>              File.open('newfile.txt', 'w') do |write|  <-- Problem
>>                      write.puts(line)
>>                         end
>>                      end
>>                    end
>>                      f.close
>>                 end
>>
>> My problem is where the "if statement" begins. I am sorry to say that my
>> compiler does not give me any error message, but the "newfile.txt" will
>> not be created and therefore not written to. This makes no sense to me
>> since I am a new beginner at Programming/scripting
>>
>> As for your code,
>>
>> "$ find . -type f -name Msg.log -exec fgrep failed {} + >newfile.txt"
>>
>> looks pretty and neat, but I am afraid it is way over my head.
>>
>> Kind regard, Robert Hansen
>
>
> Somewhere in the script i changed the working directory, so it was my
> mistake, but feel free to suggest better code. Everything will be
> appreciated as I am still learning.

It's always better to use the block form to open files. It ensures
that they are closed even if there are exceptions.
To iterate over the lines of a file one at a time I like to use File#foreach:

pattern = /(failed)/m
File.open('newfile.txt', 'w') do |out|
  Dir.glob("**/Msg.log").entries.each do |file|
    next unless File.file?(file)
    File.foreach(file) do |line|
      out.puts(line) if line.match(pattern)
    end
  end
end

Hope this helps,

Jesus.