Question

I have a simple Ruby script that looks like this

require 'csv'
while line = STDIN.gets
  array = CSV.parse_line(line)
  puts array[2]
end

But when I try using this script in a Unix pipeline like this, I get 10 lines of output, followed by an error:

ruby lib/myscript.rb < data.csv  | head

12080450
12080451
12080517
12081046
12081048
12081050
12081051
12081052
12081054
lib/myscript.rb:4:in `write': Broken pipe - <STDOUT> (Errno::EPIPE)

Is there a way to write the Ruby script in a way that prevents the broken pipe exception from being raised?

Answer 1

head is closing the standard output stream after it has read all the data it needs. You should handle the exception and stop writing to standard output. The following code will abort the loop once standard output has been closed:

while line = STDIN.gets
  array = CSV.parse_line(line)
  begin
    puts array[2]
  rescue Errno::EPIPE
    break
  end
end