问题描述
我正在尝试让 python 的 subprocess.call 方法按照 python 文档中的建议通过列表(由一系列字符串组成)接受一些 args 命令.为了在将它放入我的实际脚本之前探索这种行为，我打开了 IPython，运行了一些涉及 shell 设置和 args 命令的不同组合的命令，并得到了以下行为:
I am trying to get python's subprocess.call method to accept some args commands through a list (consisting of a sequence of strings) as advised in the python documentation. To explore this behavior before putting it into my actual script, I opened up IPython, ran some commands involving different combinations of shell settings and args commands and got the following behavior:
In [3]: subprocess.call(['ls', '-%sl' %'a'])
total 320
drwxr-xr-x 20 Kohaugustine staff 680 Oct 15 16:55 .
drwxr-xr-x 5 Kohaugustine staff 170 Sep 12 17:16 ..
-rwxr-xr-x 1 Kohaugustine staff 8544 Oct 15 16:55 a.out
-rwxr-xr-x 1 Kohaugustine staff 8544 Oct 3 10:28 ex1-6
-rw-r--r--@ 1 Kohaugustine staff 204 Oct 3 10:28 ex1-6.c
-rwxr-xr-x 1 Kohaugustine staff 8496 Oct 3 10:15 ex1-7
-rw-r--r--@ 1 Kohaugustine staff 71 Oct 3 10:15 ex1-7.c
-rwxr-xr-x 1 Kohaugustine staff 8496 Sep 12 16:22 hello
-rw-r--r--@ 1 Kohaugustine staff 58 Sep 12 16:27 hello.c
-rwxr-xr-x 1 Kohaugustine staff 8496 Sep 12 16:24 hello.o
-rwxr-xr-x 1 Kohaugustine staff 8496 Sep 12 16:24 hello_1.o
-rwxr-xr-x 1 Kohaugustine staff 8496 Sep 12 16:27 hello_2.o
-rwxr-xr-x 1 Kohaugustine staff 8496 Sep 12 16:27 hello_3.o
-rwxr-xr-x 1 Kohaugustine staff 8544 Oct 15 16:55 lesson_1-5
-rw-r--r--@ 1 Kohaugustine staff 185 Sep 28 10:35 lesson_1-5.c
-rwxr-xr-x 1 Kohaugustine staff 8496 Sep 21 10:06 temperature.o
-rw-r--r--@ 1 Kohaugustine staff 406 Sep 21 09:54 temperature_ex1-3.c
-rw-r--r--@ 1 Kohaugustine staff 582 Sep 21 10:06 temperature_ex1-4.c
-rw-r--r--@ 1 Kohaugustine staff 178 Sep 23 17:21 temperature_ex1-5.c
-rwxr-xr-x 1 Kohaugustine staff 8496 Sep 23 17:21 temperature_ex1-5.o
Out[3]: 0
In [4]: subprocess.call(['ls', '-%sl' %'a'], shell=True)
a.out ex1-7 hello.c hello_2.o lesson_1-5.c temperature_ex1-4.c
ex1-6 ex1-7.c hello.o hello_3.o temperature.o temperature_ex1-5.c
ex1-6.c hello hello_1.o lesson_1-5 temperature_ex1-3.c temperature_ex1-5.o
Out[4]: 0
In [6]: subprocess.call(['ls', '-al'])
total 320
drwxr-xr-x 20 Kohaugustine staff 680 Oct 15 16:55 .
drwxr-xr-x 5 Kohaugustine staff 170 Sep 12 17:16 ..
-rwxr-xr-x 1 Kohaugustine staff 8544 Oct 15 16:55 a.out
-rwxr-xr-x 1 Kohaugustine staff 8544 Oct 3 10:28 ex1-6
-rw-r--r--@ 1 Kohaugustine staff 204 Oct 3 10:28 ex1-6.c
-rwxr-xr-x 1 Kohaugustine staff 8496 Oct 3 10:15 ex1-7
-rw-r--r--@ 1 Kohaugustine staff 71 Oct 3 10:15 ex1-7.c
-rwxr-xr-x 1 Kohaugustine staff 8496 Sep 12 16:22 hello
-rw-r--r--@ 1 Kohaugustine staff 58 Sep 12 16:27 hello.c
-rwxr-xr-x 1 Kohaugustine staff 8496 Sep 12 16:24 hello.o
-rwxr-xr-x 1 Kohaugustine staff 8496 Sep 12 16:24 hello_1.o
-rwxr-xr-x 1 Kohaugustine staff 8496 Sep 12 16:27 hello_2.o
-rwxr-xr-x 1 Kohaugustine staff 8496 Sep 12 16:27 hello_3.o
-rwxr-xr-x 1 Kohaugustine staff 8544 Oct 15 16:55 lesson_1-5
-rw-r--r--@ 1 Kohaugustine staff 185 Sep 28 10:35 lesson_1-5.c
-rwxr-xr-x 1 Kohaugustine staff 8496 Sep 21 10:06 temperature.o
-rw-r--r--@ 1 Kohaugustine staff 406 Sep 21 09:54 temperature_ex1-3.c
-rw-r--r--@ 1 Kohaugustine staff 582 Sep 21 10:06 temperature_ex1-4.c
-rw-r--r--@ 1 Kohaugustine staff 178 Sep 23 17:21 temperature_ex1-5.c
-rwxr-xr-x 1 Kohaugustine staff 8496 Sep 23 17:21 temperature_ex1-5.o
Out[6]: 0
In [7]: subprocess.call(['ls', '-al'], shell = True)
a.out ex1-7 hello.c hello_2.o lesson_1-5.c temperature_ex1-4.c
ex1-6 ex1-7.c hello.o hello_3.o temperature.o temperature_ex1-5.c
ex1-6.c hello hello_1.o lesson_1-5 temperature_ex1-3.c temperature_ex1-5.o
Out[7]: 0
似乎每当 shell=True 时，输出似乎与以下内容相同:
It seems like whenever shell=True, the output seems to be the same as:
In [9]: subprocess.call(['ls'])
a.out ex1-7 hello.c hello_2.o lesson_1-5.c temperature_ex1-4.c
ex1-6 ex1-7.c hello.o hello_3.o temperature.o temperature_ex1-5.c
ex1-6.c hello hello_1.o lesson_1-5 temperature_ex1-3.c temperature_ex1-5.o
Out[9]: 0
我很困惑；当我设置 shell=True 时，'-a' 选项发生了什么?壳没读吗?我已经阅读了文档，它说当 shell=True 时，这意味着我指定的命令将通过 shell 执行，所以这应该意味着 ls -a 被馈送到 shell 并由 shell 执行.那么为什么会出现 [4] 和 [7] 中的行为?pydocs 也没有直接解释它(尽管它确实说明了当我们设置 shell=False 时 subpprocess 不会做的事情)；当我们让 shell=False 时是什么意思?是否在 OS 中生成了一个新进程，而没有 shell 实际控制它?
I'm puzzled; what happened to the '-a' option when I set shell=True? Didn't the shell read it? I've read the Docs and that it says that when shell=True, it means that my specified command will be executed through the shell, so it should mean that ls -a was fed to the shell and acted upon by the shell. Then why the behavior in [4] and [7] ? Also the pydocs doesn't explain it directly (although it does say what subpprocess will NOT DO when we set shell=False); what does it mean when we let shell=False? Is a new process spawned in the OS without having the shell actually control it?
另外，如果我在 [3] 和 [4] 中使用格式字符串可能看起来很尴尬，这是因为在我将使用 subprocess.call 的实际脚本中，我将不得不依赖在这些格式字符串上替换为适当的命令选项.我无法对某些命令行选项进行硬编码.对 args 使用纯字符串也是不可能的，因为在我的脚本中将有一个方法必须对命令执行列表操作.我不知道是否有更好的方法来解决这个问题，所以如果有人可以提出不同的建议，如果真的会有所帮助.
Also, in case it might seem really awkward that I'm using a format string in [3] and [4], its because in my actual script where I'll be using subprocess.call, I will have to rely on these format strings to substitute in the appropriate command options. I cannot hardcode some of the command line options. Using a pure string for args is out of the question too because in my script there will be a method that has to do list operations on the commands. I don't know if there might be a better way to go about this though, so if will really help if anyone can suggest something different.
非常感谢！
推荐答案
当shell为True时，将第一个参数追加到["/bin/sh", "-c"].如果该参数是一个列表，则结果列表是
When shell is True, the first argument is appended to ["/bin/sh", "-c"]. If that argument is a list, the resulting list is
["/bin/sh", "-c", "ls", "-al"]
也就是说，只有 ls，而不是 ls -al 用作 -c 选项的参数.-al 用作 shell 本身的第一个参数，而不是 ls.
That is, only ls, not ls -al is used as the argument to the -c option. -al is used as the first argument the shell itself, not ls.
当使用 shell=True 时，您通常只想传递一个字符串，然后让 shell 根据 shell 的正常分词规则对其进行拆分.
When using shell=True, you generally just want to pass a single string and let the shell split it according the shell's normal word-splitting rules.
# Produces ["/bin/sh", "-c", "ls -al"]
subprocess.call("ls -al", shell=True)
在您的情况下，您根本不需要使用 shell=True.
In your case, it doesn't see like you need to use shell=True at all.
这篇关于使用带有列表的 shell=True 时忽略 subprocess.call() 参数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，WP2