Set env variable inside sudo statement - Linux shell

Question

I need to modify an environment variable inside a sudo statement. The sudo statement includes some instructions.

In the example, I set the environment variable VAR1 with the value "ABC".

Then, in the sudo statement (and only here), I need to change that value to "DEF". But the value did not change after I set the value to "DEF". Echo commands return "ABC" as the value of VAR1.

How can I change/set the value of the variable inside the sudo statement?

Here an example of the code I run:

#!/bin/bash
export VAR1="ABC"

sudo -u <user> -i sh -c "
         export VAR1="DEF";
         echo $VAR1;
"

echo $VAR1;

Extra info: I tryed the option -E of sudo, to preserve the environment variable at the moment of sudo invocation (source: https://unix.stackexchange.com/questions/337819/how-to-export-variable-for-use-with-sudo/337820), but the result did not change:

#env VAR1="DEF" sudo -u <user> -E -i sh -c " [...]"

sudo env VAR1="DEF" sh -c '...' may be less trouble -- you don't need to worry about making your definitions eval-safe, which is certainly a concern if you're trying to pass data from untrusted sources to a script running with escalated privileges. Though of course that doesn't solve the problem of double quotes causing early expansion -- you do indeed need to use single quotes for your script (same as without sudo; sh -c "foo=bar; echo $foo" is always broken, sudo or no). — Charles Duffy
– Charles Duffy, Commented Jul 9, 2018 at 23:10

John Kugelman · Accepted Answer · 2018-07-09 23:15:42Z

3

Use single quotes to prevent the outer shell from interpolating $VAR1. You need $VAR1 to be passed to the inner shell so it can expand it.

sudo -u <user> -i sh -c '
         export VAR1="DEF"
         echo "$VAR1"
'

It's also a good idea to quote variable expansions to prevent globbing and splitting mishaps: write "$VAR1" instead of $VAR1.

(The semicolons aren't necessary since you have newlines.)

edited Jul 9, 2018 at 23:15

answered Jul 9, 2018 at 23:03

John Kugelman

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Comments

Gustavo Topete · Accepted Answer · 2018-07-09 23:23:03Z

0

Try this

export VAR1="ABC"

sudo -u <user> -i sh -c '
         export VAR1="DEF"
         echo "${VAR1}"
'

echo $VAR1;

as John Kugelman pointed out, you should use ' instead of " to wrap your command to avoid shell vars interpolation. Also, when referencing to VAR inside the command, use "${}" instead of $, this is what did the trick for me

answered Jul 9, 2018 at 23:23

Gustavo Topete

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9 Comments

Barmar Over a year ago

I can't think of any reason why it should matter whether you write $VAR1 or ${VAR1}. Why do you think it makes a difference?

Gustavo Topete Over a year ago

it did with me, using just $ didn't work for me, I'm using bash so there shouldn't be any problem, and I honestly don't know why is not working

Barmar Over a year ago

I just tried it. I didn't need the curly braces, but I did need to change sh to bash (combining export with the variable assignment is a bash extension) and add ; at the end of the export line (it wasn't treating the newline as a statement terminator).

Gustavo Topete Over a year ago

Mmmm, this is exactly what I run: export V=1; sudo -i bash -c 'export V=2; echo "${V}"; echo "$V";'; echo $V;, only the ${V} and the last $V (outside sudo cmd) are being printed. Do you know why? I'm not an expert with bash and this is really interesting

Barmar Over a year ago

It seems to be version-specific. I see what you see on OS X running bash 3.2.57, but not on Linux running 4.2.37.

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