Created SC2163 (markdown)

SC2163.md

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+## Exporting an expansion rather than a variable. 
+
+### Problematic code:
+
+    MYVAR=foo
+    export $MYVAR
+
+### Correct code:
+
+    MYVAR=foo
+    export MYVAR
+
+### Rationale:
+
+`export` takes a variable name, but shellcheck has noticed that you give it an expanded variable instead. The problematic code does not export `MYVAR` but a variable called `foo` if any. 
+
+### Exceptions:
+
+If you do want to export the variable's value, e.g. due to indirection, you can disable this message with a directive:
+
+    # shellcheck disable=SC2163
+    export "$MYVAR"