Use [[ -n "$whatever" ]] rather than [[ "$whatever" ]] about bashstyle

[progrium]

Mmmm, it kind of goes both ways. I like the simplicity of not using -n because for people that forget all the operators it's actually more readable. Esp if they know they can not use -n for the same thing they'll wonder "why is -n being used? what does it mean again?"

On top of that, I'm trying to focus on Bash and double-brace tests. So if your plan is to be portable to non-Bash shells, this is important, but not what my guide is optimizing for.

[stuartpb]

There's [[ ! -z "whatever" ]] if you're trying to be minimal with operators.

I think that, on the scale of "making people remember hard things", [[ ! -z is the best way to represent "string not null", but [[ -n is less of a burden to comprehend than [[ "$string" ]]. -n involves remembering one more test flag (which, when not clear from context/comments, are always one quick Google search away): [[ "$variable" ]] requires understanding that, unlike commands (including the single-brace [ test), expanding the first argument to [[ is not equivalent to substituting the content of the string, and double-brace has this whole special syntax that applies to how it evaluates arguments that doesn't apply for anything else.

And, to go back to my initial point, a forgotten operand is easier to type by accident.