Created SC2193 (markdown)

SC2193.md

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+## The arguments to this comparison can never be equal. Make sure your syntax is correct.
+
+### Problematic code:
+
+```sh
+[[ "{$var}" == "value" ]]      # Swapped around $ and {
+[[ "$(cmd1) | cmd2" == "42" ]] # Ended with ) too soon
+[[ "$var " == *.png ]]         # Trailing space
+```
+
+### Correct code:
+
+```sh
+[[ "${var}" == "value" ]]      # Correct variable expansion
+[[ "$(cmd1 | cmd2)" == "42" ]] # Correct command substitution
+[[ "$var" == *.png ]]          # No trailing space
+```
+### Rationale:
+
+ShellCheck has determined that the two values you're comparing can never be equal. 
+
+Most of the time, this happens because of a syntax issue that introduced unintended literal characters into one of the arguments.
+
+The left-hand side in the problematic examples will always contain (respectively) curly braces, pipe and trailing space. The right-hand sides are literal values and a pattern without trailing spaces, so they will never be equal. The statement is therefore useless, strongly indicating a bug. 
+
+### Exceptions:
+
+None.