[[ -v var ]] behaves differently inside bash script vs CLI

Question

I want a bash script that will set several environment variables (userid, password, token) to some default values if they don't already exist. The existence test works on the CLI but not in the script.

magilla@raspberrypi:~ $ ps -p $$
    PID TTY          TIME CMD
   3005 pts/0    00:00:05 bash
magilla@raspberrypi:~ $ echo "${BASH_VERSION}"
5.1.4(1)-release

magilla@raspberrypi:~ $ env | grep var
magilla@raspberrypi:~ $ [[ -v var ]] && echo "\${var} not defined" || echo "\${var} is defined"
${var} not defined

magilla@raspberrypi:~ $ cat myscript
#!/bin/bash
[[ -v var ]] && echo "\${var} not defined" || echo "\${var} is defined"
magilla@raspberrypi:~ $ bash myscript
${var} is defined
magilla@raspberrypi:~ $ bash < myscript
${var} is defined

Answer 1

Apparently var is set in your interactive shell (it's not in the environment though). Then [[ -v var ]] returns success and echo "\${var} not defined" is executed.

You see not defined because the logic of your code is wrong.

In the script var is not set, [[ -v var ]] returns failure and echo "\${var} is defined" is executed.

You see is defined because again the logic is wrong. The following logic makes sense:

[[ -v var ]] && echo "\${var} is defined" || echo "\${var} not defined"

It's opposite to the logic of your code.