Using Ruby command line options by Arjan van der Gaag http://arjanvandergaag.nl/blog/using-ruby-command-line-options.html

before.rb

#!/usr/bin/env ruby -w
# This tranforms input files that look like CSV and strips comments and
# filters out every line not about "Suriname".

# Define some basic variables that control how records and fields
# are defined.
input_record_separator  = "\n"
field_separator         = ','
output_record_separator = "\n"
output_field_separator  = ';'
filename = ARGV[0]

File.open(filename, 'r+') do |f|

  # Read the entire contents of the file in question
  # in an input array.
  input = f.readlines(input_record_separator)
  output = ''

  # Loop over all the lines in the file with a counter
  input.each_with_index do |last_read_line, i|

    # Remove the ending newline from the line for easier
    # processing.
    last_read_line.chomp!(input_record_separator)

    # Extract all fields in this record.
    fields = last_read_line.split(field_separator)

    # Only proceed for non-comment lines about Suriname
    if fields[5] == 'Suriname' && !(last_read_line =~ /^# /)

      # Write the output lines including the line number
      # and combine fields using our custom separator
      fields.unshift i
      output << fields.join(output_field_separator)
      output << output_record_separator
    end
  end

  # Rewind back to the start of the file and replace all its
  # contents with the content in `output`.
  f.rewind
  f.write output
  f.flush
  f.truncate(f.pos)
end