實現簡單的shell sed替換功能

#腳本文件，用於實現文件裏簡單的字符串替換
import sys
f = open('yesterday', 'r', encoding='utf-8')
f_new = open('yesterday.bak', 'w', encoding='utf-8')

find_str = sys.argv[1]
replace_str = sys.agrv[2]

for line in f:
    if find_str in line:
        line = line.replace(find_str, replace_str)
    f_new.write(line)

f.close()
f_new.close()