Created SC2170 (markdown)

SC2170.md

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+## Numerical -eq does not dereference in [..]. Expand or use string operator.
+
+### Problematic code:
+
+```sh
+read -r n
+if [ n -lt 0 ]
+then
+   echo "bad input"
+fi
+```
+
+### Correct code:
+
+```sh
+read -r n
+if [ "$n" -lt 0 ]
+then
+   echo "bad input"
+fi
+```
+### Rationale:
+
+You are comparing a string value with a numerical operator, such as `-eq`, `-ne`, `-lt` or `-gt`.
+
+In `[[ .. ]]`, this would automatically dereference the string, looking to see if there are variables by that name.
+
+In `[ .. ]`, which you are using, the string is just treated as an invalid number.
+
+If you want to compare numbers, expand yourself (e.g. use `$var` instead of `var`). If you are trying to compare strings and not numbers, use `=`, `!=` `\<` or `\>` instead.
+
+### Exceptions:
+
+None.