Please do not count on 22LR for any sort of self defense purposes. It’s a great round for shooting paper targets and small critters, but against a human it has the stopping power of a letter opener. Sure, it might stop someone if you hit just the right spot, or pain might shock someone inexperienced into pausing long enough for you to run, but you don’t really want to be counting on either of those in a life or death scenario.

You’re probably wanting [ -z "${VAR1}" -a -z "${VAR2}" ]. Note in bash that there are minor differences in how [ ] and [[ ]] tests are handled. You can pull up a handy cheat sheet of the operands on most distros by running man test, though you’ll need to read through the CONDITIONAL EXPRESSIONS section of man bash if you want to see the minor differences of the single vs double square bracket commands (mostly whether locale applies to string order, as well as whether operands are evaluated in numeric comparisons).