Python的子进程不允许使用shell = True进行进程替换?

2022-01-18 00:00:00 python shell subprocess bash process-substitution

问题描述

这是一个在 Bash 中运行良好的进程替换的玩具示例:

Here is a toy example of process substitution that works fine in Bash:

$ wc -l <(pwd)
1 /proc/self/fd/11

那么，为什么在 shell=True 的 Python 子进程中调用同一命令时会出现语法错误?

So why does the same command give a syntax error when invoked from Python's subprocess with shell=True? 

>>> subprocess.check_call('wc -l <(pwd)', shell=True)
/bin/sh: 1: Syntax error: "(" unexpected
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/path/to/my/python/lib/python3.5/subprocess.py", line 581, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command 'wc -l <(pwd)' returned non-zero exit status 2

解决方案

/bin/sh: 1: 语法错误:("意外

/bin/sh: 1: Syntax error: "(" unexpected

你有一个 bashism.根据 POSIX 是无效的，这是 /bin/sh 实现的.

You have a bashism. It is not valid according to POSIX, which is what /bin/sh implements.

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