Created SC1028 (markdown)

SC1028.md

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+## In [..] you have to escape \\( \\) or preferably combine [..] expressions.
+
+### Problematic code:
+
+```sh
+[ -e ~/.bashrc -a ( -x /bin/dash -o -x /bin/ash ) ]
+```
+
+### Correct code:
+
+In POSIX:
+```sh
+[ -e ~/.bashrc ] &&  { [ -x /bin/dash ] || [ -x /bin/ash ]; }
+```
+
+Obsolete XSI syntax:
+```sh
+[ -e ~/.bashrc -a \( -x /bin/dash -o -x /bin/ash \) ]
+```
+
+### Rationale:
+
+`[` is implemented as a regular command, so `(` is not special.
+
+The preferred way is not to group inside `[ .. ]` and instead compose multiple `[ .. ]` statments using the shell's `&&`, `||` and `{ ..; }` syntax, since this is well defined by POSIX.
+
+Some shells, such as Bash, support grouping with `\( .. \)`, but this is an obsolete XSI-only extension.
+
+### Exceptions:
+
+None