Created SC2233 (markdown)

SC2233.md

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+## Remove superfluous `(..)` around condition.
+
+### Problematic code:
+
+```sh
+if ([ "$x" -gt 0 ])
+then true; fi
+```
+
+### Correct code:
+
+```sh
+if [ "$x" -gt 0 ]
+then true; fi
+```
+
+### Rationale:
+
+The shell syntax is `if cmd`, `elif cmd`, `while cmd` and `until cmd` without any parentheses. Instead, parentheses are an independent construct used to create subshells.
+
+ShellCheck has noticed that you're wrapping `(..)` around one or more test commands. This is unnecessary, and the resulting fork adds quite a lot of overhead:
+
+```
+$ i=0; time while ( [ "$i" -lt 10000 ] ); do i=$((i+1)); done
+real    0m6.998s
+user    0m3.453s
+sys     0m3.464s
+
+$ i=0; time while [ "$i" -lt 10000 ]; do i=$((i+1)); done
+real    0m0.055s
+user    0m0.054s
+sys     0m0.001s
+```
+
+Just delete the surrounding `(..)` since they serve no purpose and only slows the script down.
+
+### Exceptions:
+
+None.
+
+### Related resources:
+
+* Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!