Created attachment 71040 [details]
Better check the -u and -c options and document -c

The xdg-su man page says:

>  xdg-su [-u user] -c command
>
>  xdg-su provides a graphical dialog that prompts the user for a
>  password to run command as user or as root if no user was specified.

The '-c' option is not documented and this does not clearly say if one should use 'xdg-su -c echo HelloWorld' or 'xdg-su -c "echo HelloWorld"'.

The example at the end of the page seems to imply the latter but then it's only one example and one may think that a second example could show that the other option is valid too.

>  xdg-su -u root -c "/opt/shinythings/bin/install-GUI --install fast"


I'll further note that the situation is muddied by the fact that

  xdg-su -c sh -c 'echo HelloWorld'

is equivalent to

  xdg-su -c foo -c 'echo HelloWorld'

and to

  xdg-su -c 'echo HelloWorld'

due to the limited parameter checking.


I'm attaching a patch as a starting point for a fix.