Python subprocess.run shell kwarg behavior

Question

There has been a lot of questions regarding shell keyword argument. But I still don't really get it especially if we use the sequence argument instead of the string.

My understanding is that if shell=False , the subprocess module will run the executable in args[0] and pass the rest as arguments to the executable. But if we run it with shell=True , it will be ran as something like "sh -c {}".format(format_escaping(args)) .

But why does this happen?

# Ran in OSX

subprocess.run(["touch", "12; touch 34"]) # successfuly make the file '12; touch 34'

subprocess.run(["touch", "56; touch 78"], shell=True) # does not work:
# usage:
# touch [-A [-][[hh]mm]SS] [-acfhm] [-r file] [-t [[CC]YY]MMDDhhmm[.SS]] file ...
# CompletedProcess(args=['touch', '123; touch 456'], returncode=1)

What actually happen in subprocess.run(["touch", "56; touch 79"], shell=True) ?

Answer 1

我认为使用shell=True ，成功操作只会首先运行touch的第一个parameter ，因此您会从命令中获取帮助消息，而是尝试如下操作：

subprocess.run("touch 56; touch 78", shell=True)

Answer 2

The behavior when you pass in a list with shell=True is platform-dependent. On Unix-like platforms, Python simply passes in the first argument of the list. On Windows, it happens to work, though it probably shouldn't.