printjson.rb

#!/usr/bin/env ruby
# -*- ruby -*-

# Usage: 
#   ruby printjson.rb field1 fields2 file
#
# if file == '-' then read from stdin
#
# Install the json gem first:
#
#   gem install json
#
# Build your own console twitter-wall with
#
# curl -s http://stream.twitter.com/1/statuses/filter.json?track=<terms-to-track> -u<username>:<password> | ruby printjson.rb created_at text -

require 'rubygems'
require 'json'

fields = ARGV[0...-1]
file = ARGV[-1]

def print_field(json, fields)
  fields = fields.split('.')
  for f in fields
    json = json[f]
  end
  return json
end

def print_json(line, fields)
  begin
    json = JSON.parse(line)
    puts fields.map {|field| print_field(json, field)}.join "\t"
  rescue JSON::ParserError
  end
end

if file == '-'
  $stdin.each_line do |line| print_json(line, fields) end
else
  open(file).each_line do |line| print_json(line, fields) end
end