用管道链接几个Popen命令

Question

我知道如何使用cmd = subprocess.Popen和subprocess.communicate运行命令。大多数情况下，我将使用shlex.split标记的字符串用作Popen的'argv'参数。“ ls -l”的示例：import subprocessimport shlexprint subprocess.Popen(shlex.split(r'ls -l'), stdin = subprocess.PIPE, stdout = subprocess.PIPE, stderr = subprocess.PIPE).communicate()[0]但是，管道似乎不起作用...例如，以下示例返回注释：import subprocessimport shlexprint subprocess.Popen(shlex.split(r'ls -l | sed "s/a/b/g"'), stdin = subprocess.PIPE, stdout = subprocess.PIPE, stderr = subprocess.PIPE).communicate()[0]你能告诉我我做错了吗？谢谢

Answer 1

我认为您想在此处实例化两个单独的Popen对象，一个用于“ ls”，另一个用于“ sed”。您需要将第一个Popen对象的stdout属性作为stdin参数传递给第二个Popen对象。

例：

p1 = subprocess.Popen('ls ...', stdout=subprocess.PIPE)

p2 = subprocess.Popen('sed ...', stdin=p1.stdout, stdout=subprocess.PIPE)

print p2.communicate()

如果您有更多命令，则可以保持链接的方式：

p3 = subprocess.Popen('prog', stdin=p2.stdout, ...)

请参阅子流程文档以获取有关如何使用子流程的更多信息。

Answer 2

我已经做了一些功能来帮助管道，希望对您有所帮助。它将根据需要链接Popens。

from subprocess import Popen, PIPE

import shlex

def run(cmd):

  """Runs the given command locally and returns the output, err and exit_code."""

  if "|" in cmd:    

    cmd_parts = cmd.split('|')

  else:

    cmd_parts = []

    cmd_parts.append(cmd)

  i = 0

  p = {}

  for cmd_part in cmd_parts:

    cmd_part = cmd_part.strip()

    if i == 0:

      p[i]=Popen(shlex.split(cmd_part),stdin=None, stdout=PIPE, stderr=PIPE)

    else:

      p[i]=Popen(shlex.split(cmd_part),stdin=p[i-1].stdout, stdout=PIPE, stderr=PIPE)

    i = i +1

  (output, err) = p[i-1].communicate()

  exit_code = p[0].wait()

  return str(output), str(err), exit_code

output, err, exit_code = run("ls -lha /var/log | grep syslog | grep gz")

if exit_code != 0:

  print "Output:"

  print output

  print "Error:"

  print err

  # Handle error here

else:

  # Be happy :D

  print output

Answer 3

shlex 仅根据shell规则拆分空间，但不处理管道。

但是，它应该以这种方式工作：

import subprocess

import shlex

sp_ls = subprocess.Popen(shlex.split(r'ls -l'), stdin = subprocess.PIPE, stdout = subprocess.PIPE, stderr = subprocess.PIPE)

sp_sed = subprocess.Popen(shlex.split(r'sed "s/a/b/g"'), stdin = sp_ls.stdout, stdout = subprocess.PIPE, stderr = subprocess.PIPE)

sp_ls.stdin.close() # makes it similiar to /dev/null

output = sp_ls.communicate()[0] # which makes you ignore any errors.

print output

根据help(subprocess)的

Replacing shell pipe line

-------------------------

output=`dmesg | grep hda`

==>

p1 = Popen(["dmesg"], stdout=PIPE)

p2 = Popen(["grep", "hda"], stdin=p1.stdout, stdout=PIPE)

output = p2.communicate()[0]

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