Python小程序之sed命令替换

需求：

　　编写sed命令脚本

代码如下

# Author:Lee Sir

import sys,os

des_file = r'E:StartPythonday3	est.txt'
des_file1 = r'E:StartPythonday3	est1.txt'

parameter = ['0','Somehow','123',des_file]

def usage(parameter):
    if len(parameter) == 4:
        if isinstance(parameter[1],str) and isinstance(parameter[2],str):
            old_str = parameter[1]
            new_str = parameter[2]
            if os.path.exists(parameter[3]):
                des_file = parameter[3]
                return True, old_str, new_str, des_file
    return False

def check_string_exist(old,file):
    with open(file,encoding='utf-8') as fd:
        for line in fd:
            if old not in line:
                return False
            else:
                return True

def replace(old,new,file):
    with open(file,'r+',encoding='utf-8') as fd,open(des_file1,'w+',encoding='utf-8') as fd1:
        for line in fd:
            if old in line:
                new_line = line.replace(old,new)
            else:
                new_line = line
            print(new_line)
            fd1.write(new_line)

def main():
    result = usage(parameter)
    if result:
        if check_string_exist(result[1],result[3]):
            replace(result[1],result[2],result[3])
        else:
            print('the %s is not found in %s ' % (result[1],result[3]))
    else:
        exit('USAGE: %s  old_str  new_str  des_file' % sys.argv[0])

if __name__ == '__main__':
    main()