How do sudo environment variables work in linux?

Question

I'm currently perplexed by the following:

sudo echo $MYVAR

outputs my variable from my .bashrc,

but

sudo ./test.sh

does not, where test.sh is the below executable:

#!/bin/sh
echo $MYVAR                 

I'm running Ubuntu 14.04. Can someone enlighten me as to what's going on here?

Answer 1

When you run sudo echo $MYVAR, the environment variable is expanded in your shell ... before the sudo command gets to see it.

When you run a script using sudo, that script only sees the environment variables that sudo has included in the environment. The default is to not to include them ... for security reasons.

The sudo command has an option -E that tells the command that the user wants to pass through all environment variables. The sudoers configuration file may or may not permit this.