Created SC2081 (markdown)

SC2081.md

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+## `[ .. ]` can't match globs. Use `[[ .. ]]` or grep.
+
+### Problematic code:
+
+```sh
+if [ $var == *[^0-9]* ]
+then
+  echo "$var is not numeric"
+fi 
+```
+
+### Correct code:
+
+```sh
+if [[ $var == *[^0-9]* ]]
+then
+  echo "$var is not numeric"
+fi 
+```
+### Rationale:
+
+`[ .. ]` aka `test` can not match against globs. 
+
+In bash/ksh, you can instead use `[[ .. ]]` which supports this behavior.
+
+In sh, you can rewrite to use `grep`. 
+
+### Exceptions:
+
+None. If you are not trying to match a glob, quote the argument (e.g. `[ $var == '*' ]` to match literal asterisk.