Why is zenity executed twice?

Question

I have the following script (called ./script), which I want to run with $( ./script ) because the result should set some environment variable. Strangely the zenity dialog is displayed twice before the script terminates when I run it in $( ), while it is only displayed once if I run it as is.

#!/bin/bash

export select=`zenity --list --column=select "option1" "option2"`
echo "export SELECTION_VAR=$select"

Can anybody explain, why it is executed twice and how I can avoid this?

Answer 1

Since script is trying to affect the parent environment, you need to eval its resulting output. This pattern is common, and you can find a similar case done by the keychain tool. If you invoke keychain, it spits out to stdout an eval-able statement like:

SSH_AGENT_PID=1234; export SSH_AGENT_PID;

So for your case, you’d invoke script with:

% eval $(./script)  # choose option2
% echo $SELECTION_VAR
option2

Also, you shouldn’t need the export on your select= line.