Created SC2165 (markdown)

SC2165.md

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+## This nested loop overrides the index variable of its parent.
+
+And companion warning "This parent loop has its index variable overridden."
+
+### Problematic code:
+
+    for((i=0; i<10; i++))
+    do
+      for i in *
+      do
+        echo "$i"
+      done
+    done
+
+### Correct code:
+
+    for((i=0; i<10; i++))
+    do
+      for j in *
+      do
+        echo "$j"
+      done
+    done
+
+### Rationale:
+
+When nesting loops, especially arithmetic for loops, using the same loop variable can cause unexpected results.
+
+In the problematic code, `i` will contain the last filename from the inner loop, which will be interpreted as a value in the next iteration out the outer loop. This results in either an infinite loop or a syntax error, depending on whether the last filename is a valid shell variable name.
+
+In nested for-in loops, variable merely shadow each other and won't cause infinite loops or syntax errors, but reusing the variable name is rarely intentional.
+
+### Exceptions:
+
+None.