Created SC2299 (markdown)

SC2299.md

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+## Parameter expansions can't be nested. Use temporary variables.
+
+### Problematic code:
+
+```sh
+path="/path/to/MyFile.mp3"
+echo "Playing ${${path##*/}%.*}"    # Expect: Playing MyFile
+```
+
+### Correct code:
+
+```sh
+path="/path/to/MyFile.mp3"
+tmp=${path##*/}
+echo "Playing ${tmp%.*}"
+```
+
+### Rationale:
+
+ShellCheck found what appears to be a nested parameter expansion. In the example, it was hoping to combine `${var##*/}` to strip the directory and `${var%.*}` to strip the extension.
+
+Parameter expansions can't be nested. Use temporary variables instead, so that each parameter expansion only does a single operation.
+
+Alternatively, if the goal is to dynamically generate and expand a variable name, see [[SC2082]].
+
+### Exceptions:
+
+None
+
+### Related resources:
+
+* Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!