Python：通过读取标准输出来关闭 for 循环

Question

import os

dictionaryfile = "/root/john.txt"
pgpencryptedfile = "helloworld.txt.gpg"

array = open(dictionaryfile).readlines()


for x in array:
    x = x.rstrip('\n')
    newstring = "echo " + x + " | gpg --passphrase-fd 0 " + pgpencryptedfile
    os.popen(newstring)

我需要在 for 循环中创建一些东西来读取 gpg 的输出。当gpg输出这个字符串gpg: WARNING: message was not integrity protected时，我需要循环关闭并打印成功！

我该怎么做，背后的原因是什么？

谢谢大家！

Answer 1

import subprocess


def check_file(dictfile, pgpfile):
    # Command to run, constructed as a list to prevent shell-escaping accidents
    cmd = ["gpg", "--passphrase-fd", "0", pgpfile]

    # Launch process, with stdin/stdout wired up to `p.stdout` and `p.stdin`
    p = subprocess.Popen(cmd, stdin = subprocess.PIPE, stdout = subprocess.PIPE)

    # Read dictfile, and send contents to stdin
    passphrase = open(dictfile).read()
    p.stdin.write(passphrase)

    # Read stdout and check for message
    stdout, stderr = p.communicate()
    for line in stdout.splitlines():
        if line.strip() == "gpg: WARNING: message was not integrity protected":
            # Relevant line was found
            return True

    # Line not found
    return False

然后使用：

not_integrity_protected = check_file("/root/john.txt", "helloworld.txt.gpg")
if not_integrity_protected:
    print "Success!"

如果 "gpg: WARNING:" 消息实际上是在 stderr 上（我怀疑是这样），请将 subprocess.Popen 行更改为：

p = subprocess.Popen(cmd, stdin = subprocess.PIPE, stderr = subprocess.PIPE)

..还有从stdout到stderr的for循环，像这样：

for line in stderr.splitlines():

Answer 2

使用subprocess.check_output 调用gpg 并根据其输出中断循环。

类似这样的东西（未经测试，因为我对gpg一无所知）：

import subprocess

dictionaryfile = "/root/john.txt"
pgpencryptedfile = "helloworld.txt.gpg"

with open(dictionaryfile, 'r') as f:
    for line in f:
        x = line.rstrip('\n')
        cmd = ["echo " + x + " | gpg --passphrase-fd 0 " + pgpencryptedfile]
        output = subprocess.check_output(cmd, shell=True)
        if 'gpg: WARNING: message was not integrity protected' in output:
            break

Answer 3

您可以使用subprocess 模块，它允许您使用：

subprocess.call(args, *, stdin, stdout, stderr, shell)

（如何使用参数请参见Python Documentation。）

这很好，因为您可以轻松读取您调用的任何程序的退出代码。

例如，如果您将 'newstring' 更改为：

"echo " + x + " | gpg --passphrase-fd 0 " + pgpencryptedfile | grep 'gpg: WARNING: message was not integrity protected'

grep 如果有匹配则返回 0，如果没有匹配则返回 1。 (Source)

这个 grep 的退出代码将从 subprocess.call() 函数返回，您可以轻松地将其存储在变量中并使用 if 语句。

编辑：正如 Matthew Adams 在下面提到的，您还可以阅读 gpg 本身的退出代码。