Python中的subprocess.call没有这样的文件或目录错误

Question

一般来说，我尝试使用 Bash 从命令行而不是 Python 进行读取，这样我就有了制表符补全功能。我想以最简单的方式做到这一点。但是，我无法让以下代码正常工作，我想了解导致问题的原因。

Python 脚本：

from subprocess import call
call(['read', '-ep', 'Path:', 'temporaryPath'])
print temporaryPath

错误回溯：

Traceback (most recent call last):
  File "tmp.py", line 2, in <module>
    call(['read', '-ep', 'Path:', 'temporaryPath'])
  File "/usr/lib64/python2.6/subprocess.py", line 478, in call
    p = Popen(*popenargs, **kwargs)
  File "/usr/lib64/python2.6/subprocess.py", line 642, in __init__
    errread, errwrite)
  File "/usr/lib64/python2.6/subprocess.py", line 1238, in _execute_child
    raise child_exception
OSError: [Errno 2] No such file or directory

Answer 1

您正在尝试调用 read，这是一个内置的 shell：

$ type read
read is a shell builtin

而且这个特殊的内置 shell 没有等效的程序：

$ which read
$ 

因此，根据strace，Python 将无法在您的PATH 环境变量中找到它：

[pid 17266] execve("/usr/local/bin/read", ["read", "-ep", "Path:", "temporaryPath"], [/* 70 vars */]) = -1 ENOENT (No such file or directory)
[pid 17266] execve("/usr/bin/read", ["read", "-ep", "Path:", "temporaryPath"], [/* 70 vars */]) = -1 ENOENT (No such file or directory)
[pid 17266] execve("/bin/read", ["read", "-ep", "Path:", "temporaryPath"], [/* 70 vars */]) = -1 ENOENT (No such file or directory)
[pid 17266] execve("/usr/local/games/read", ["read", "-ep", "Path:", "temporaryPath"], [/* 70 vars */]) = -1 ENOENT (No such file or directory)
[pid 17266] execve("/usr/games/read", ["read", "-ep", "Path:", "temporaryPath"], [/* 70 vars */]) = -1 ENOENT (No such file or directory)
[…]
[pid 17266] write(4, "OSError:", 8 <unfinished ...>

但如果你明确要求 Python 使用 shell 来执行你的命令，shell 本身将能够运行其内置的 read：

$ python3
Python 3.5.3 (default, Jan 19 2017, 14:11:04) 
[GCC 6.3.0 20170118] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import subprocess
>>> subprocess.call('read', shell=True)
/bin/sh: 1: read: arg count
2
>>> subprocess.call('read foo', shell=True)
hello world
0

您现在遇到了一个新问题：内置的 shell read 将读取的值存储为一个 shell 变量，当调用 subprocess.call 后，shell 将立即死亡，该变量将消失。

哦，在read shell 内置你也没有完成。如果您想以交互方式向用户询问某些内容，或者如果不需要交互，您可能应该只使用input，只需使用argparse 来解析用户作为命令行参数提供的内容，这样用户就会有一些键入参数时的 shell 完成，通常不是在标志上，因为用户 shell 不知道它们，而是在路径上。