python - 我无法在子进程中从 os.system 获得相同的结果

Question

我想从 os.system 转换成子进程如下

os.system("egrep 'Invalid user' /home/bits/Desktop/Assessment/auth.log | cut -d ' ' -f 11 >tempfile.txt ") 

它有效，但是当我使用子进程编写相同的语句时，它会创建一个空文件，有人知道为什么以及如何解决这个问题吗？谢谢

a1=subprocess.Popen(["egrep \"Invalid users\" /home/bits/Desktop/Assessment/auth.log"],shell=True,stdout=subprocess.PIPE)   ### instead of /home/bits/Desktop/Assessment/auth.log please modify with your full path of auth.log
a2=subprocess.Popen(["cut -d \" \" -f 11 > /home/bits/Desktop/Assessment/rezolvare/tempfile.txt"],shell=True,stdin=a1.stdout,stdout=subprocess.PIPE)

Answer 1

您应该将输出文件作为 stdout 提供:

with open("/home/bits/Desktop/Assessment/rezolvare/tempfile.txt", "wb") as output:
    a1 = subprocess.Popen(["egrep",  "Invalid users", "/home/bits/Desktop/Assessment/auth.log"], stdout=subprocess.PIPE)
    a2 = subprocess.Popen(["cut", "-d", " ", "-f", "11"], stdin=a1.stdout, stdout=output)

用纯 python 编写更简单:

with open("/home/bits/Desktop/Assessment/auth.log") as lines:
    with open("/home/bits/Desktop/Assessment/rezolvare/tempfile.txt", "wb") as output:
        for line in lines:
            if "Invalid users" in line:
                output.write(line.split(" ")[10] + "\n")