启动包含管道命令的子进程时找不到文件错误 [英] File not found error when launching a subprocess containing piped commands

问题描述

我需要运行命令 date |grep -o -w '"+tz+"'' |wc -w 在我的本地主机上使用 Python.我正在使用 subprocess 模块，并使用 check_output 方法，因为我需要捕获相同的输出.

但是它给我一个错误:

回溯(最近一次调用最后一次):文件test.py"，第 47 行，在 <module> 中check_timezone()文件test.py"，第 40 行，在 check_timezone计数 = subprocess.check_output(命令)文件/usr/lib/python2.7/subprocess.py"，第 537 行，在 check_output 中进程 = Popen(stdout=PIPE, *popenargs, **kwargs)文件/usr/lib/python2.7/subprocess.py"，第 679 行，在 __init__ 中错误读取，错误写入)文件/usr/lib/python2.7/subprocess.py"，第 1249 行，在 _execute_child 中提出 child_exception-OSError: [Errno 2] 没有那个文件或目录

解决方案

您必须添加 shell=True 才能执行 shell 命令.check_output 正在尝试查找名为的可执行文件:date |grep -o -w '"+tz+"'' |wc -w 他找不到它.(不知道你为什么从错误消息中删除了基本信息).

查看两者的区别:

<预><代码>>>>subprocess.check_output('date | grep 1')回溯(最近一次调用最后一次):文件<stdin>"，第 1 行，在 <module> 中文件/usr/lib/python3.4/subprocess.py"，第 603 行，在 check_output 中使用 Popen(*popenargs, stdout=PIPE, **kwargs) 作为进程:文件/usr/lib/python3.4/subprocess.py"，第 848 行，在 __init__ 中restore_signals，start_new_session)文件/usr/lib/python3.4/subprocess.py"，第 1446 行，在 _execute_child 中引发 child_exception_type(errno_num, err_msg)FileNotFoundError: [Errno 2] 没有这样的文件或目录:'date |格雷普 1'

还有:

<预><代码>>>>subprocess.check_output('date | grep 1', shell=True)b'gio 19 giu 2014, 14.15.35, CEST '

阅读有关常用参数的文档以了解更多信息关于 shell 参数的信息以及它如何改变其他参数的解释.

<小时>

请注意，您应该尽量避免使用 shell=True，因为生成 shell 可能存在安全隐患(即使您不执行像 Shellshock 这样的不受信任的输入攻击，仍然可以执行！).

subprocess 模块的文档有一小部分是关于更换外壳管道.您可以通过在 python 中生成两个进程并使用 subprocess.PIPE 来实现:

date_proc = subprocess.Popen(['date'], stdout=subprocess.PIPE)grep_proc = subprocess.check_output(['grep', '1'], stdin=date_proc.stdout, stdout=subprocess.PIPE)date_proc.stdout.close()输出 = grep_proc.communicate()[0]

您可以编写一些简单的包装函数来轻松定义管道:

导入子流程从 shlex 导入拆分从集合导入namedtuple从 functools 导入减少proc_output = namedtuple('proc_output', 'stdout stderr')定义管道(starter_command，*commands):如果不是命令:尝试:starter_command, *commands = starter_command.split('|')除了属性错误:经过starter_command = _parse(starter_command)starter = subprocess.Popen(starter_command, stdout=subprocess.PIPE)last_proc = reduce(_create_pipe, map(_parse, commands), starter)返回 proc_output(*last_proc.communicate())def _create_pipe(上一个，命令):proc = subprocess.Popen(command, stdin=previous.stdout, stdout=subprocess.PIPE)以前的.stdout.close()退货流程def_parse(cmd):尝试:返回拆分(cmd)除了例外:返回命令

有了这个，你可以编写 pipeline('date | grep 1') 或 pipeline('date', 'grep 1') 或 pipeline(['date'], ['grep', '1'])

I need to run the command date | grep -o -w '"+tz+"'' | wc -w using Python on my localhost. I am using subprocess module for the same and using the check_output method as I need to capture the output for the same.

However it is throwing me an error :

Traceback (most recent call last):
  File "test.py", line 47, in <module>
    check_timezone()
  File "test.py", line 40, in check_timezone
    count = subprocess.check_output(command)
  File "/usr/lib/python2.7/subprocess.py", line 537, in check_output
    process = Popen(stdout=PIPE, *popenargs, **kwargs)
  File "/usr/lib/python2.7/subprocess.py", line 679, in __init__
    errread, errwrite)
  File "/usr/lib/python2.7/subprocess.py", line 1249, in _execute_child
    raise child_exception-
OSError: [Errno 2] No such file or directory

解决方案

You have to add shell=True to execute a shell command. check_output is trying to find an executable called: date | grep -o -w '"+tz+"'' | wc -w and he cannot find it. (no idea why you removed the essential information from the error message).

See the difference between:

>>> subprocess.check_output('date | grep 1')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.4/subprocess.py", line 603, in check_output
    with Popen(*popenargs, stdout=PIPE, **kwargs) as process:
  File "/usr/lib/python3.4/subprocess.py", line 848, in __init__
    restore_signals, start_new_session)
  File "/usr/lib/python3.4/subprocess.py", line 1446, in _execute_child
    raise child_exception_type(errno_num, err_msg)
FileNotFoundError: [Errno 2] No such file or directory: 'date | grep 1'

And:

>>> subprocess.check_output('date | grep 1', shell=True)
b'gio 19 giu 2014, 14.15.35, CEST
'

Read the documentation about the Frequently Used Arguments for more information about the shell argument and how it changes the interpretation of the other arguments.

---

Note that you should try to avoid using shell=True since spawning a shell can be a security hazard (even if you do not execute untrusted input attacks like Shellshock can still be performed!).

The documentation for the subprocess module has a little section about replacing the shell pipeline. You can do so by spawning the two processes in python and use subprocess.PIPE:

date_proc = subprocess.Popen(['date'], stdout=subprocess.PIPE)
grep_proc = subprocess.check_output(['grep', '1'], stdin=date_proc.stdout, stdout=subprocess.PIPE)
date_proc.stdout.close()
output = grep_proc.communicate()[0]

You can write some simple wrapper function to easily define pipelines:

import subprocess
from shlex import split
from collections import namedtuple
from functools import reduce

proc_output = namedtuple('proc_output', 'stdout stderr')


def pipeline(starter_command, *commands):
    if not commands:
        try:
            starter_command, *commands = starter_command.split('|')
        except AttributeError:
            pass
    starter_command = _parse(starter_command)
    starter = subprocess.Popen(starter_command, stdout=subprocess.PIPE)
    last_proc = reduce(_create_pipe, map(_parse, commands), starter)
    return proc_output(*last_proc.communicate())

def _create_pipe(previous, command):
    proc = subprocess.Popen(command, stdin=previous.stdout, stdout=subprocess.PIPE)
    previous.stdout.close()
    return proc

def _parse(cmd):
    try:
        return split(cmd)
    except Exception:
        return cmd

With this in place you can write pipeline('date | grep 1') or pipeline('date', 'grep 1') or pipeline(['date'], ['grep', '1'])

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