Created SC1097 (markdown)

SC1097.md

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+## Unexpected ==. For assignment, use =. For comparison, use [/[[.
+
+### Problematic code:
+
+    var==value
+
+### Correct code:
+
+Assignment:
+
+    var=value
+
+Comparison:
+
+    [ "$var" = value ] 
+
+### Rationale:
+
+ShellCheck has noticed that you're using `==` in an unexpected way. The two most common reasons for this is:
+
+* You wanted to assign a value but accidentally used `==` instead of `=`.
+
+* You wanted to compare two values, but neglected to use `[ .. ]` or `[[ .. ]]`.
+
+### Exceptions:
+
+If you wanted to assign a literal equals sign, use quotes to make this clear:
+
+    var="=sum(A1:A10)"