Created SC2254 (markdown)

SC2254.md

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+## Quote expansions in case patterns to match literally rather than as a glob.
+
+### Problematic code:
+
+```sh
+case $input in
+  -       ) echo "Reading from stdin..." ;;
+  $output ) echo "Input should be different from output" ;;
+esac
+```
+
+### Correct code:
+
+```sh
+case $input in
+  -         ) echo "Reading from stdin..." ;;
+  "$output" ) echo "Input should be different from output" ;;
+esac
+```
+### Rationale:
+
+When unquoted variables and command expansions are used in case branch patterns, they will be interpreted as globs. 
+
+This can lead to some surprising behavior, such as `case $x in $x) trigger;; esac` not triggering in some cases, such as when `x='Pride and Prejudice [1813].epub'`.
+
+To match the literal content of the variable or expansion, make sure to double quote the expansion.
+
+### Exceptions:
+
+If you intended to match a dynamically generated pattern, you can ignore this suggestion with a directive.
+
+### Related resources:
+
+* [[SC2053]], where the same effect can be seen with `[[ $x = $x ]]`.
+* Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!