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+# Use `$(...)` notation instead of legacy backticked `` `...` ``.
+### Problematic code
+```sh
+echo "You are running on `uname`"
+```
+### Correct code
+```sh
+echo "You are running on $(uname)"
+```
+### Rationale
+Backtick command substitution `` `...` `` is legacy syntax with several issues.
+1. It has a series of undefined behaviors related to quoting in POSIX.
+1. It imposes a custom escaping mode with surprising results.
+1. It's exceptionally hard to nest.
+`$(...)` command substitution has none of these problems, and is therefore strongly encouraged.
+### Exceptions
+None.
+### Related resources:
+
+* [BashFaq: Why is `$(...)` preferred over `` `...` `` (backticks)?](http://mywiki.wooledge.org/BashFAQ/082)
+* [StackOverflow: What is the difference between $(command) and `` `command` `` in shell programming?](https://stackoverflow.com/questions/4708549/shell-programming-whats-the-difference-between-command-and-command)
+* [shfmt](https://github.com/mvdan/sh) will automatically convert the legacy syntax
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