Python：理解linux和freeBSD上os.system的行为

我在脚本中使用os.system（）调用shell命令。我编写了一个示例脚本来了解os.system（）如何执行该命令

import os
os.system("sleep 20")

我在freeBSD和linux机器上运行了上述代码，然后执行了ps aux | grep sleep，结果如下：

freeBSD:

:~]# ps aux | grep sleep
root  94832  0.0  0.0  2768   984   0  S+    5:31AM   0:00.00 sleep 20 

linux（ubuntu）：

在这两台机器中，Shell都是bash

既然

os.system（cmd）

在子shell中执行

cmd

，那么在freeBSD上不也应该有

sh-c sleep 20

进程运行吗？有人能解释一下这种行为吗？

“sh”在Linux和FreeBSD上是不一样的。Linux的/bin/sh进行fork（）调用，但FreeBSD的/bin/sh进行execve（）调用以执行命令，因此它不会生成Linux中显示的新进程

Linux：

sh-4.1$ sh --version
sh --version
GNU bash, version 4.1.2(1)-release (x86_64-redhat-linux-gnu)
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

os.system（）

本质上是

system（3）

的传递，因此您的答案将在那里。

sh-4.1$ sh --version
sh --version
GNU bash, version 4.1.2(1)-release (x86_64-redhat-linux-gnu)
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

man sh
DESCRIPTION
     The sh utility is the standard command interpreter for the system.  The
     current version of sh is close to the IEEE Std 1003.1 (“POSIX.1”)
     specification for the shell.  It only supports features designated by
     POSIX, plus a few Berkeley extensions.  This man page is not intended to
     be a tutorial nor a complete specification of the shell
HISTORY
     A sh command, the Thompson shell, appeared in Version 1 AT&T UNIX.  It was
     superseded in Version 7 AT&T UNIX by the Bourne shell, which inherited the
     name sh.

     This version of sh was rewritten in 1989 under the BSD license after the
     Bourne shell from AT&T System V Release 4 UNIX.

AUTHORS
     This version of sh was originally written by Kenneth Almquist.