if statement with variable comparison not working in bash shell

Question

I'm trying to write a very simple script to check whether iptables are already updated for Synergy to work. The current script is:

if [[ $SYNERGY = "yes" ]]
then
    echo "Synergy is active"
else
    sudo iptables -I INPUT -p tcp --dport 24800 -j ACCEPT
    export SYNERGY=yes
fi

But it does not work (I'm always asked for the sudo password each time I open a new terminal)
I also tried with this modified version, but the result is the same

syn="yes"
if [ "$SYNERGY" = "$syn" ]
then
    echo "Synergy is active"
else
    sudo iptables -I INPUT -p tcp --dport 24800 -j ACCEPT
    export SYNERGY=yes
fi

Where is the issue?

it might be asking root password to execute the command sudo iptables -I INPUT -p tcp --dport 24800 -j ACCEPT — RBH
– RBH, Commented Dec 3, 2014 at 14:11
@anubhava variable SYNERGY is set in the export command in the else statement — sthor69
– sthor69, Commented Dec 3, 2014 at 16:07
@RBH scope of the script is just to avoid passing the sudo password each time I open a new terminal — sthor69
– sthor69, Commented Dec 3, 2014 at 16:09

Etan Reisner · Accepted Answer · 2014-12-03 14:12:34Z

3

If you are expecting this to be run from one terminal/shell session and to affect other unrelated terminals/shell sessions then the issue is that that isn't how export works.

export sets the variable in the environment of the current process so that any processes spawned from this process also have it in their environment. Notice how I said "spawned from"? It only applies to processes that process spawns. Unrelated processes aren't affected.

If you want something globally checkable then you either need a flag/lock/state file of some sort or an actual runtime check of the iptables configuration.

answered Dec 3, 2014 at 14:12

Etan Reisner

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7 Comments

sthor69 Over a year ago

My first attempt was exactly to check iptables, but I soon understood it was the wrong way to approach the problem, as to check iptables I need to be root and I fall again in the password checking each time I open a new terminal. Do you have any suggestion to find a simple solution? As you understood I didn't work too much in linux scripting

Etan Reisner Over a year ago

@sthor69 Why is this something you need to be doing often? Can you not just set this as the normal configuration of the system and be done with it? As I said in my answer you can use a flag/lock/state file instead of an exported variable for the check (but then you also need to ensure that the file is cleaned up when appropriate).

sthor69 Over a year ago

As I said I'm rather a newbie in linux scripting, so I'd like to find a solution working with file and I don't know how to manage flags and states. Before starting working on them, I tried another solution that seems to work, putting the iptables command in /etc/profile. Is there any drawbacks with this solution?

Etan Reisner Over a year ago

@sthor69 flags and state aren't magic terms. They are descriptive ones. The point was that you get to maintain a file (somewhere in the filesystem) which indicates that the iptables rule has been added and test that file instead of the variable. And yes, putting it in /etc/profile is not a good solution but it is on the right path to making it a proper system setting. What distribution is this?

sthor69 Over a year ago

It is an Ubuntu 14.04

|

sthor69 · Accepted Answer · 2014-12-05 16:25:21Z

0

Just to help those who have the same question, this is how I managed to persist firewall settings:

sudo apt-get install iptables-presistent

and then the rules specified in the files rules.v4 or rules.v6 in /etc/iptables are automatic loaded at startup

answered Dec 5, 2014 at 16:25

sthor69

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