python 的流程自动化

Question

我正在尝试编写一个 python 脚本来启动一个进程并在后面执行一些操作。我想通过脚本自动执行的命令在图中用红色圈出。问题是在执行第一个命令后，qemu 环境将是运行而其他命令应该在 qemu 环境中执行。所以我想知道如何通过 python 中的脚本执行这些命令？因为据我所知，我可以执行第一个命令，但我不知道在进入 qemu 环境时如何执行这些命令。

你能帮我看看我该怎么做吗？

Answer 1

别忘了 Python 包含电池。查看标准库中的 Suprocess module 。管理流程有很多陷阱，模块会处理所有这些问题。

您可能想要启动一个 qemu 进程并将下一个命令发送到其标准输入 (stdin)。子流程模块将允许您这样做。看到qemu有command line options连接到stdi：-chardev stdio ,id=id

Answer 2

首先想到的是 pexpect, a quick search on google turned up this blog post automatically-testing-vms-using-pexpect-and-qemu，这似乎与您所做的大致相同：

import pexpect

image = "fedora-20.img"
user = "root"
password = "changeme"

# Define the qemu cmd to run
# The important bit is to redirect the serial to stdio
cmd = "qemu-kvm"
cmd += " -m 1024 -serial stdio -net user -net nic"
cmd += " -snapshot -hda %s" % image
cmd += " -watchdog-action poweroff"

# Spawn the qemu process and log to stdout
child = pexpect.spawn(cmd)
child.logfile = sys.stdout

# Now wait for the login
child.expect('(?i)login:')

# And login with the credentials from above
child.sendline(user)
child.expect('(?i)password:')
child.sendline(password)
child.expect('# ')

# Now shutdown the machine and end the process
if child.isalive():
    child.sendline('init 0')
    child.close()

if child.isalive():
    print('Child did not exit gracefully.')
else:
    print('Child exited gracefully.')

您也可以使用 subprocess.Popen 来完成，检查 (qemu) 行的标准输出并写入标准输入。大致是这样的：

from subprocess import Popen,PIPE

# pass initial command as list of individual args
p = Popen(["./tracecap/temu","-monitor",.....],stdout=PIPE, stdin=PIPE)
# store all the next arguments to pass
args = iter([arg1,arg2,arg3])
# iterate over stdout so we can check where we are
for line in iter(p.stdout.readline,""):
    # if (qemu) is at the prompt, enter a command
    if line.startswith("(qemu)"):
        arg = next(args,"") 
        # if we have used all args break
        if not arg:
            break
        # else we write the arg with a newline
        p.stdin.write(arg+"\n")
    print(line)# just use to see the output

其中 args 包含所有后续命令。

python 的流程自动化

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