4.实现简单的shell sed替换功能

 # -*- coding:utf-8 -*-
 # Author: JACK ZHAO

 # 程序1: 实现简单的shell sed替换功能

 import  sys

 #判断参数个数
 if len(sys.argv) != 3:
     print("Usage: python_sed.py 'old string' 'net string'")
     exit()
 #读取所有行至内存中
 with open("yesterday","r",encoding='utf-8') as f:
     lines = f.readlines()

 #重新生成文件yesterday,读取内存中内容至新文件
 with open("yesterday","w",encoding='utf-8') as f:
     for line in lines:
         if sys.argv[1] in line:
             line = line.replace(sys.argv[1],sys.argv[2]) #sys.argv[1]:要替换的内容 sys.argv[2]:替换后的内容
         f.write(line)