SC2254 – ShellCheck Wiki

Quote expansions in case patterns to match literally rather than as a glob.

Problematic code:

case $input in
  -       ) echo "Reading from stdin..." ;;
  $output ) echo "Input should be different from output" ;;
esac

Correct code:

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.

SC2053, where the same effect can be seen with [[ $x = $x ]].
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