From: Karthikeyan Balasubramanian <karthikb@...>
Date: 2009-09-23T18:55:24+09:00
Subject: Mini Parser

Hi all,

  I have a requirement.  I have a to read some commands from file and
output as another file.  For example if the input file is like below:

6
WRITE  Today
WRITE  is
UNDO  1
WRITE  my
UNDO  2
WRITE birthday

Output file will be like this.

Today is birthday

WRITE basically write's string after the command and UNDO will undo N
number of line preceding it.  Complexity here is last UNDO has to UNDO
the previous undo's work.

So far I have been able to only come up with the below code:

begin
  file = File.new("abc.txt", "r")
  while (line = file.gets)
    line.grep(/WRITE/) { |s|
      puts s
    }
  end
  file.close

rescue => err
  puts "Exception: #{err}"
  err
end

Any help here?
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