#!/bin/env python3

import sys

if __name__ == '__main__':
    if len(sys.argv) < 3:
        sys.exit()

    data = []
    with open(sys.argv[3], 'r+') as file:
        data = file.read()
        data = data.replace(sys.argv[1], sys.argv[2])
        file.close()
    with open(sys.argv[3], 'w') as filew:
        filew.write(data)