Created SC2323 (markdown)

SC2323.md

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+##  `a[(x)]` is the same as `a[x]`. Prefer not wrapping in additional parentheses.
+
+Similarly `$(( (x) ))` is the same as `$(( x ))`, `(( (x) ))` is the same as `(( x ))`.
+
+
+### Problematic code:
+
+```sh
+array[(x+1)]=val
+echo $(( (x+1) ))
+```
+
+### Correct code:
+
+```sh
+array[x+1]=val
+echo $((x+1))
+```
+
+### Rationale:
+
+ShellCheck found an entire arithmetic expression wrapped in parentheses. This does not serve a purpose since the expression is already clearly delimited by the construct it's in, such as `array[..]=` or `$((..))` in the example.
+
+Note: ShellCheck does *not* warn about redundant parentheses in subexpressions, such as `(a*b)+c`. Feel free to use parentheses to clarify the order of operations any way you'd like. ShellCheck only emits this suggestion when the *entire* expression is wrapped *twice*.
+
+### Exceptions:
+
+If you prefer having an extra layer of parentheses for stylistic reasons, you can [[ignore]] this message.
+
+### Related resources:
+
+* Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!