#!/usr/bin/env python
# Exercise 9
# sed command

import re
import sys
import argparse
from pathlib import Path


def parse(expression):
    try:
        match = re.fullmatch(r's/(.*)/(.*)/(g{0,1})', expression)
        count = 0 if match.group(3) == "g" else 1
        return {
            "rgx": re.compile(match.group(1)),
            "rep": match.group(2),
            "n": count
        }
    except Exception:
        print(f"sed: expresión «{expression}» inválida")
        sys.exit(1)


parser = argparse.ArgumentParser()
parser.add_argument("stream", default=sys.stdin, nargs="*")
parser.add_argument(
    "-e", "--expression", required=True, type=str, action="append"
)
args = parser.parse_args()
res = ""

for exp in args.expression:
    exp = parse(exp)
    for stream in args.stream:
        if isinstance(args.stream, list):
            stream = Path(stream).read_text()
        else:
            stream = stream.strip()
        if res == "":
            res = stream
        res = re.sub(exp["rgx"], exp["rep"], res, count=exp["n"])
print(res)