#/usr/bin/env python3

import fileinput
from argparse import ArgumentParser

parser = ArgumentParser()
parser.add_argument('-s', '--separator', default=",", help='Separator')
parser.add_argument('files', metavar='FILE', nargs='*', help='files to read, if empty, stdin is used')
args = parser.parse_args()

print(args.separator.join(line.strip() for line in fileinput.input(files=args.files)))