Question

我目前正在使用

p1 = subprocess.Popen(['ps', 'ax'], stdout=subprocess.PIPE)
p2 = subprocess.Popen(['grep', 'bash'], stdin=p1.stdout,    stdout=subprocess.PIPE)
p3 = subprocess.Popen(['wc', '-l'], stdin=p2.stdout, stdout=subprocess.PIPE)
count = int(p3.stdout.read())

if count == 2:
   print count
   print "yes"
else:
   print "fail"

检查我的python当前是否已经运行。它工作正常。

但是，我想知道我是否可以将p1 p2和p3合并为一行。

我试过

p = subprocess.Popen(['ps ax | grep bash | wc -l'], stdout=subprocess.PIPE)

还有更多，但它不起作用。有没有办法将所有这3个组合成一行？

Answer 1

如果将|关键字参数传递给shell=True，则只能使用shell样式的管道（Popen）：

p = subprocess.Popen('ps ax | grep bash | wc -l', stdout=subprocess.PIPE, shell=True)

否则，您传递的整个字符串将被视为可执行文件的名称，这将失败，因为您没有名为ps ax | grep bash | wc -l的程序。

此外，您不应该将命令作为带有shell=True的列表传递，您只需传递一个字符串。

另一个注意事项：您可能需要调整命令才能使其正常工作，因此grep bash命令本身不会计入ps ax | grep bash的输出中。这样做的一个技巧是使用ps ax | grep [b]ash。此外，使用shell=True可能最终会启动bash实例来运行命令，因此您可能需要使用if count == 3而不是if count == 2。

完全放弃：

p = subprocess.Popen('ps ax | grep [b]ash | wc -l', stdout=subprocess.PIPE, shell=True)

count = int(p.stdout.read())

if count == 2: # Or maybe 3?
   print count
   print "yes"
else:
   print "fail"

修改

这是在我的机器上运行不同版本代码的输出

>>> p1 = subprocess.Popen(['ps', 'ax'], stdout=subprocess.PIPE) >>> p2 = subprocess.Popen(['grep', 'bash'], stdin=p1.stdout, stdout=subprocess.PIPE) >>> p3 = subprocess.Popen(['wc', '-l'], stdin=p2.stdout, stdout=subprocess.PIPE); p3.stdout.read() '42\n' >>> p1 = subprocess.Popen(['ps', 'ax'], stdout=subprocess.PIPE) >>> p2 = subprocess.Popen(['grep', 'bash'], stdin=p1.stdout, stdout=subprocess.PIPE) >>> p3 = subprocess.Popen(['wc', '-l'], stdin=p2.stdout, stdout=subprocess.PIPE); p3.stdout.read() '42\n' >>> p1 = subprocess.Popen(['ps', 'ax'], stdout=subprocess.PIPE) >>> p2 = subprocess.Popen(['grep', 'bash'], stdin=p1.stdout, stdout=subprocess.PIPE) >>> p3 = subprocess.Popen(['wc', '-l'], stdin=p2.stdout, stdout=subprocess.PIPE); p3.stdout.read() '42\n' >>> p1 = subprocess.Popen(['ps', 'ax'], stdout=subprocess.PIPE) >>> p2 = subprocess.Popen(['grep', 'bash'], stdin=p1.stdout, stdout=subprocess.PIPE) >>> p3 = subprocess.Popen(['wc', '-l'], stdin=p2.stdout, stdout=subprocess.PIPE); p3.stdout.read() '42\n' >>> p1 = subprocess.Popen(['ps', 'ax'], stdout=subprocess.PIPE) >>> p2 = subprocess.Popen(['grep', 'bash'], stdin=p1.stdout, stdout=subprocess.PIPE) >>> p3 = subprocess.Popen(['wc', '-l'], stdin=p2.stdout, stdout=subprocess.PIPE); p3.stdout.read() '42\n' >>> p = subprocess.Popen('ps -ef | grep bash | wc -l ', stdout=subprocess.PIPE, shell=True) ; print(''.join(p.stdout.readlines())) 44 >>> p = subprocess.Popen('ps -ef | grep bash | wc -l ', stdout=subprocess.PIPE, shell=True) ; print(''.join(p.stdout.readlines())) 44 >>> p = subprocess.Popen('ps -ef | grep bash | wc -l ', stdout=subprocess.PIPE, shell=True) ; print(''.join(p.stdout.readlines())) 44 >>> p = subprocess.Popen('ps -ef | grep [b]ash | wc -l ', stdout=subprocess.PIPE, shell=True) ; print(''.join(p.stdout.readlines())) 42 >>> p = subprocess.Popen('ps -ef | grep [b]ash | wc -l ', stdout=subprocess.PIPE, shell=True) ; print(''.join(p.stdout.readlines())) 42 >>> p = subprocess.Popen('ps -ef | grep [b]ash | wc -l ', stdout=subprocess.PIPE, shell=True) ; print(''.join(p.stdout.readlines())) 42

Answer 2

这是一个明显的答案。我所做的就是用第一个作业替换第二个p1和p2。

p3 = subprocess.Popen(['wc', '-l'], stdin=subprocess.Popen(['grep', 'bash'], \
     stdin=subprocess.Popen(['ps', 'ax'], stdout=subprocess.PIPE).stdout, \
     stdout=subprocess.PIPE).stdout, stdout=subprocess.PIPE)

如何将三个subprocess.popen组合成一行？

2 个答案: