Using popen & grep

ruby-talk
1

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

···

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2

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

cmd="grep -i #{ARGV[0]} #{ARGV[1]}"
puts cmd

results = IO.popen(cmd, "r")
while output = results.gets
     puts output
end
results.close

you should chech ARGV is correct. you can run cmd on console to see
result,cheers!

···

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Posted via http://www.ruby-forum.com/\.

3

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

···

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

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