Created SC2108 (markdown)

SC2108.md

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+## In [\[..]], use && instead of -a.
+
+### Problematic code:
+
+    [[ "$1" = "-v" -a -z "$2" ]]
+
+### Correct code:
+
+    [[ "$1" = "-v" && -z "$2" ]]
+
+### Rationale:
+
+`-a` for logical AND is not supported in a `[[ .. ]]` expression. Use `&&` instead.
+
+### Exceptions:
+
+None.