echo $USER/ sudo echo $USER

jamescondron · 06-03-2009, 06:41 PM

Could anybody explain why in a script run as sudo, echo $USER will return root, but sudo echo $USER will always return the username running sudo. For a more clear question:

Code:

jc@jcmain:~$ sudo echo $USER
jc
jc@jcmain:~$ sudo ./sudo_demo.sh 
root
jc@jcmain:~$ cat sudo_demo.sh
#!/usr/bin/env bash
echo $USER

I essentially need the code running as sudo to return 'jc', checking the wd is not viable here, either. Ideas?

bigearsbilly · 06-03-2009, 06:53 PM

well $USER is set by the shell.

I reckon...
the line is evaluated first by the shell and all the variables
interpolated, then the command is forked off to execute

so:

sudo echo $USER

runs as:

sudo echo jc

it happens before the sudo

jamescondron · 06-03-2009, 07:05 PM

That actually sounds reasonable put that way, I really hadn't thought it like that. Ah well, I may just script in an extra arg to handle this stuff instead, feels messier, but nevermind

raconteur · 06-03-2009, 07:06 PM

The difference is because you are telling sudo to apply the privilege elevation to the echo command in the first case, and the script in the second case.
The echo command is running as root, but it is reporting the current shell user. If you were to modify the code for echo to report its user, it would be root.
I don't know of any elegant method to get the invoker's UID or LOGNAME. I'd probably use a brute-force method of some sort. Hopefully someone else here may know a better trick.

edit: heh, bigearsbilly beat me to it ;-)

bigearsbilly · 06-03-2009, 07:28 PM

maybe try the id command?

jamescondron · 06-03-2009, 10:12 PM

id does exactly the same thing when called in a script run as sudo

ntubski · 06-03-2009, 11:58 PM

Code:

 $ man sudo
...
ENVIRONMENT
...
SUDO_USER       Set to the login of the user who invoked sudo