用管道链接多个 Popen 命令

Question

我知道如何使用 cmd = subprocess.Popen 然后使用 subprocess.communicate 运行命令。 大多数时候，我使用 shlex.split 标记的字符串作为 Popen 的“argv”参数。 使用“ls -l”的示例：

import subprocess
import shlex
print 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 subprocess
import shlex
print subprocess.Popen(shlex.split(r'ls -l | sed "s/a/b/g"'), stdin = subprocess.PIPE, stdout = subprocess.PIPE, stderr = subprocess.PIPE).communicate()[0]

您能告诉我我做错了什么吗？

谢谢

Answer 1

我认为您想在这里实例化两个单独的 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。

示例：

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，您可以继续以这种方式链接：

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

请参阅子流程文档了解有关如何使用子流程的更多信息。

Answer 2

我做了一个小功能来帮助管道，希望它有帮助。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规则分割空格，但不处理管道。

然而，它应该这样工作：

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)'s

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]

HTH

Answer 4

"""
Why don't you use shell

"""

def output_shell(line):

    try:
        shell_command = Popen(line, stdout=PIPE, stderr=PIPE, shell=True)
    except OSError:
        return None
    except ValueError:
        return None

    (output, err) = shell_command.communicate()
    shell_command.wait()
    if shell_command.returncode != 0:
        print "Shell command failed to execute"
        return None
    return str(output)

Answer 5

感谢@hernvnc、@glglgl 和@Jacques Gaudin 的回答。我修复了@hernvnc 的代码。他的版本在某些情况下会导致挂起。

import shlex
from subprocess import PIPE
from subprocess import Popen
def run(cmd, input=None):
    """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:
            if input:
                p[i]=Popen(shlex.split(cmd_part),stdin=PIPE, stdout=PIPE, stderr=PIPE)
            else:
                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
    # close the stdin explicitly, otherwise, the following case will hang.
    if input:
        p[0].stdin.write(input)
        p[0].stdin.close()
    (output, err) = p[i-1].communicate()
    exit_code = p[0].wait()
    return str(output), str(err), exit_code

# test case below
inp = b'[  CMServer State   ]\n\nnode        node_ip         instance state\n--------------------------------------------\n1  linux172 10.90.56.172    1        Primary\n2  linux173 10.90.56.173    2        Standby\n3  linux174 10.90.56.174    3        Standby\n\n[    ETCD State     ]\n\nnode        node_ip         instance state\n--------------------------------------------------\n1  linux172 10.90.56.172    7001     StateFollower\n2  linux173 10.90.56.173    7002     StateLeader\n3  linux174 10.90.56.174    7003     StateFollower\n\n[   Cluster State   ]\n\ncluster_state   : Normal\nredistributing  : No\nbalanced        : No\ncurrent_az      : AZ_ALL\n\n[  Datanode State   ]\n\nnode        node_ip         instance state            | node        node_ip         instance state            | node        node_ip         instance state\n------------------------------------------------------------------------------------------------------------------------------------------------------------------------\n1  linux172 10.90.56.172    6001     P Standby Normal | 2  linux173 10.90.56.173    6002     S Primary Normal | 3  linux174 10.90.56.174    6003     S Standby Normal'
cmd = "grep -E 'Primary' | tail -1 | awk '{print $3}'"

run(cmd, input=inp)