ci: Fix SDK test script unbound variable error

[Ali-Piccioni]

ci: Fix SDK test script unbound variable error

The problem with the original script is that we set set -u at the top which treats unset variables as errors.
This causes an error when evaluating "$DFX_VER" inside the if statement, because DFX_VER is unset.

${var+x} is a parameter expansion which evaluates to nothing if var is unset, and substitutes the string x otherwise.
https://stackoverflow.com/questions/3601515/how-to-check-if-a-variable-is-set-in-bash

[luc-mercier]

Can you enlighten me? I don't know what "+x" means.

[Ali-Piccioni]

Can you enlighten me? I don't know what "+x" means.

@luc-mercier

The problem with the original script is that we set set -u at the top which treats unset variables as errors.
This causes an error when evaluating "$DFX_VER" inside the if statement, because DFX_VER is unset.

${var+x} is a parameter expansion which evaluates to nothing if var is unset, and substitutes the string x otherwise.

https://stackoverflow.com/questions/3601515/how-to-check-if-a-variable-is-set-in-bash

[luc-mercier]

Can you enlighten me? I don't know what "+x" means.

@luc-mercier

The problem with the original script is that we set set -u at the top which treats unset variables as errors.
This causes an error when evaluating "$DFX_VER" inside the if statement, because DFX_VER is unset.

${var+x} is a parameter expansion which evaluates to nothing if var is unset, and substitutes the string x otherwise.

https://stackoverflow.com/questions/3601515/how-to-check-if-a-variable-is-set-in-bash

Thanks for the explanation! Makes sense. I copied it to the PR description: those types of essential explanations belong to the PR descriptions more than they do to the comment thread.