Translate .csv files to .json objects using the first line of the csv file as a list of keys

csv_to_json.rb

# csv_to_json.rb
# a simple utility to translate csv files to json objects 
# using the first line of the csv file as a list of keys

# The keys in the first line of the csv file are downcased and
# underscored (ex: "First Name" => "first_name")

# Example usage:
# csv_to_json.rb my_csv_file.csv 
# => outputs JSON interpretation of my_csv_file.csv to STDOUT
# csv_to_json.rb *.csv 
# => translates each .csv file to a .json file and writes 
# these files to disk

# Example translation:
# =test.csv
# First Name, Last Name, Email
# John, Doe, [email protected]
# Jane, Doe, [email protected]
# 
# $ ruby csv_to_json.rb test.csv > test.json
# or
# $ csv_to_json *.csv
# 
# =test.json
# [{"first_name":"John","last_name":" Doe","email":" [email protected]"},{"first_name":"Jane","last_name":" Doe","email":" [email protected]"}]

def parse_csv(filename)
  require 'csv'
  keys = nil
  data = []
  CSV.foreach(filename) do |row|
    # set keys as the first row
    if keys.nil?
     keys = row.map{|k| k.downcase.strip.gsub(" ", '_')} 
     next
    end

    item = {}
    row.each_with_index{|e, i|
      item[keys[i]] = e
    }
    data << item
  end
  data
end

def csv_to_json(filename)
  require 'json'
  parse_csv(filename).to_json
end

# ===main===
if ARGV.size == 1
  # print a single file to STDOUT
  puts csv_to_json(ARGV[0])
elsif ARGV.size > 1
  # we recieved a block of filenames
  # translate each one and write it to disk
  ARGV.each do |filename|
    print "Processing \"#{filename}\" => "
    output_filename = filename.sub(/\.csv$/, ".json")
    File.open(output_filename, 'w'){|f|
      f.puts csv_to_json(filename)
    }
    puts "\"#{output_filename}\""
  end
end