How to do complex conditionals in bash? (mix of 'and' &&, 'or' || ...)

You almost got it:

if [[ "$a" == "something" || ($n == 2 && "$b" == "something_else") ]]; then

In fact, the parentheses can be left out because of operator precedence, so it might also be written as

if [[ "$a" == "something" || $n == 2 && "$b" == "something_else" ]]; then

bash syntax conditional

if [[ "$a" == "something" ]] || [[ $n == 2 && "$b" == "something_else" ]]; then  ...fi

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