From: Florian Gross <flgr@...>
Date: 2004-03-06T13:54:42+09:00
Subject: Re: Ruby translation for UNIX scripting command

Mark Hubbart wrote:

> If, on the other hand, you want a script that you can call like this:
> 
> % myscript input_file output_file
> 
> then you will be needing to read up a little more in ruby, I think. But 
> here's some code for an example:
> 
>   filtered_data = File.open("input_file") do |file|
>     file.read.grep(/pattern/).map{|line| line.split[3]}.join "\n"
>   end
> 
>   File.open("output_file") do |file|
>     file.write filtered_data
>   end

This can be simplified to:

   filtered_data = File.read("input_file").grep(/pattern/) \
     .map { |line| line.split[3] }

   File.open("output_file") do |file|
     file.puts filtered_data
   end


It might however be better to do all this in one pass over the data 
without using any buffers -- I'd do that like this:

   filtered_data = Array.new
   File.foreach("input_file") do |line|
     if md = /^(#\w+) ([\d:]+) (<\w+>) (.*?)$/.match(line)
       channel, time, nick, text = md.captures
       filtered_data << text
     end
   end

   File.open("output_file") do |file|
     file.puts filtered_data
   end

This implementation does also allow one to keep a part of the matching 
line not surrounded by whitespace. (Which means that one could also use 
it on CSV data or similar input.)