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lang-bash
$boolis set to either 1 or a null string,((bool))works just like[[ $bool ]], which is the same as[[ -n $bool ]]. To test for a false value,((! bool))is equal to[[ ! $bool ]]. It can even be used for parameter expansion such asecho "${bool:+This variable is true}". The values 0 and 1 do not provide this much flexibility.