su-和su --login有什么区别？

从su的手册页：

For  backward  compatibility, su defaults to not change the current directory
and to only set the environment variables HOME and SHELL (plus USER and LOGNAME
if the target user is not root).  It is recommended to always use the 
--login option (instead of  its  shortcut -) to avoid side effects caused
by mixing environments.

...

-, -l, --login
    Start the shell as a login shell with an environment similar to a real login:

        o      clears all the environment variables except TERM

        o      initializes the environment variables HOME, SHELL, USER, LOGNAME, and PATH

        o      changes to the target user's home directory

        o      sets argv[0] of the shell to '-' in order to make the shell a login shell

很难说出-和之间--login（或据称只是-l）之间是否存在任何差异。即，手册页显示为“而不是其快捷方式-”，但是所有这些选项都组合在一起，如果完全存在，我看不到差异的解释。

UPD我检查了问题，该问题应该可以解决我的问题。问题基本上是关于su和之间的区别su -。我问的是su -和之间的区别su --login。所以不，它根本无法解决。

Debian的手动输入似乎更具启发性：

   -, -l, --login
       Provide an environment similar to what the user would expect had the user logged
       in directly.

       When - is used, it must be specified before any username. For portability it is
       recommended to use it as last option, before any username. The other forms (-l
       and --login) do not have this restriction.

没有区别，就像跑步；

echo bob | grep -v bob
echo bob | grep --invert-match bob

只是速记...