Created SC2235 (markdown)

SC2235.md

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+## Use `{ ..; }` instead of `(..)` to avoid subshell overhead.
+
+### Problematic code:
+
+```sh
+([ "$x" ] || [ "$y" ]) && [ "$z" ]
+```
+
+### Correct code:
+
+```sh
+{ [ "$x" ] || [ "$y" ]; } && [ "$z" ]
+```
+
+### Rationale:
+
+You appear to be using `(..)` to group test commands. This creates a subshell, making it unnecessarily slow. Avoid this by using `{ ..; }` to group.
+
+Be careful to note that unlike `(..)`, this requires both a space after the `{` and a semicolon before the `}`.
+
+For example, `(cmd)`, `(cmd;)` and `( cmd )` are all valid, but `{cmd}`, `{cmd;}` and `{ cmd }` are all syntax errors because they lack either or both of the spaces and semicolon. The correct form is `{ cmd; }`
+
+Here's a small benchmark showing that the subshell version is more than 100x slower:
+
+```
+$ i=0; time for i in {1..10000}; do ([ "$x" ] || [ "$y" ]) && [ "$z" ]; done
+real    0m7.122s
+user    0m4.204s
+sys     0m2.825s
+
+$ i=0; time for i in {1..10000}; do { [ "$x" ] || [ "$y" ]; } && [ "$z" ]; done
+real    0m0.055s
+user    0m0.055s
+sys     0m0.000s
+```
+
+
+
+### Exceptions:
+
+None.
+
+### Related resources:
+
+* Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!