old_contents: import json
  import argparse
  
  parser = argparse.ArgumentParser()
  parser.add_argument('json_file', nargs='+')
  parser.add_argument('output_file')
  
  if __name__ == "__main__":
      args = parser.parse_args()
  
      list_all = []
      for jf in args.json_file:
          with open(jf) as in_f:
              list_all += json.load(in_f)
  
      with open(args.output_file, 'w') as out_f:
          json.dump(list_all, out_f)
  
new_contents: import json
  import argparse
  
  parser = argparse.ArgumentParser()
  parser.add_argument('json_file', nargs='+')
  parser.add_argument('output_file')
  
  if __name__ == "__main__":
      args = parser.parse_args()
  
      list_all = []
      for jf in args.json_file:
          with open(jf) as in_f:
              file_jsons = json.load(in_f)
              for fj in file_jsons:
                  if fj not in list_all:
                      list_all.append(fj)
  
      with open(args.output_file, 'w') as out_f:
          json.dump(list_all, out_f)
  
subject: Remove duplicate JSON gaferences when concatenating