Created SC2149 (markdown)

SC2149.md

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+## Remove $/${} for numeric index, or escape it for string.
+
+### Problematic code:
+
+    # Regular array
+    index=42
+    echo $((array[$index]))
+
+or
+
+    # Associative array
+    index=banana
+    echo $((array[$index]))
+
+### Correct code:
+    
+    # Regular array
+    index=42
+    echo $((array[index]))
+
+or
+
+    # Associative array
+    index=banana
+    echo $((array[\$index]))
+
+### Rationale:
+
+For a numerically indexed array, the `$` is mostly pointless and can be removed like in [[SC2004]].
+
+For associative arrays, the `$` should be escaped to avoid accidental dereferencing:
+
+    declare -A array
+    index='$1'
+    array[$index]=42   
+    echo "$(( array[$index] ))"    # bash: array: bad array subscript   
+    echo "$(( array[\$index] ))"   # 42
+
+### Contraindications
+
+None.