python - 子进程 Popen 中 "&>"的奇怪行为

Question

我注意到 subprocess.Popen() 调用中的“&>”运算符会立即提供返回代码，即使在直觉上不应该这样做的情况下也是如此。举例说明:

>>> import subprocess
>>> a = subprocess.Popen("sleep 5 > a.txt", shell = True)
>>> print(a.poll()) # immediately try printing
None
>>> print(a.poll()) # wait 5 seconds
0
>>> a = subprocess.Popen("sleep 5 &> a.txt", shell = True)
>>> print(a.poll()) # immediately try printing
0
>>> a = subprocess.Popen("sleep 5 > a.txt 2>&1", shell = True) # this should be the same as using &>
>>> print(a.poll()) # immediately try printing
None
>>> print(a.poll()) # wait 5 seconds
0

我在 Python 3.5.2 上运行它。我的机器默认运行 bash。

有谁知道为什么子流程在这里不支持正确的“&>”行为？

Answer 1

那是因为 &> 是一个 bashism，当 shell=True。

来自subprocess.Popen docs :

The executable argument specifies a replacement program to execute. It is very seldom needed. When shell=False, executable replaces the program to execute specified by args. However, the original args is still passed to the program. Most programs treat the program specified by args as the command name, which can then be different from the program actually executed. On POSIX, the args name becomes the display name for the executable in utilities such as ps. If shell=True, on POSIX the executable argument specifies a replacement shell for the default /bin/sh.

修复方法是显式指定executable参数，例如:

subprocess.Popen("sleep 5 &> a.txt", shell=True, executable='/bin/bash')