From: Robert Klemme <shortcutter@...>
Date: 2010-04-13T15:35:08+09:00
Subject: Re: Using popen & grep

On 04/12/2010 01:40 AM, Dan King wrote:
> I'm relatively new to ruby and to practice I've put together the code
> below - it's supposed take two arguments then apply it to a grep command
> and display the output. Currently, nothing is outputted to the console.
> Anyone see what I'm doing wrong, thanks.
> 
>   1 #!/usr/bin/ruby
>   2
>   3 results = IO.popen("grep -i #{ARGV[0]} #{ARGV[1]}", "r")
>   4 while output = results.gets
>   5     puts output
>   6 end
>   7 results.close

A few remarks: the block form of IO.popen is more robust because it 
ensures proper closing of file handles.  Also, using an array as first 
argument avoids quoting issues - you need 1.9 for this.  Thus you could do:

IO.popen ["grep", "-i", *ARGV[0..1]], "r" do |io|
   io.each_line do |line|
     puts line
   end
end

However, much easier would be to read and grep yourself in Ruby:

rx = Regexp.new(ARGV[0], Regexp::IGNORECASE)

File.foreach ARGV[1] do |line|
   puts line if rx =~ line
end

Kind regards

	robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/