Created SC2111 (markdown)

SC2111.md

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+## ksh does not allow 'function' keyword and '()' at the same time.
+
+### Problematic code:
+
+```sh
+#!/bin/ksh
+function foo() {
+  echo "Hello World"
+}
+```
+
+### Correct code:
+
+```sh
+# POSIX sh function
+foo() {
+  echo "Hello World"
+}
+```
+
+or
+
+```sh
+# ksh extended function
+function foo {
+  echo "Hello World"
+}
+```
+
+### Rationale:
+
+Ksh allows two ways of defining functions: POSIX sh style `foo() { ..; }` and Ksh specific `function foo { ..; }`.
+
+ShellCheck found a function definition that uses both at the same time, `function foo() { ..; }` which is not allowed. Use one or the other.
+
+Note that the two are not identical, for example:
+
+* Using `typeset` in a `function foo` will create a local variable, while in `foo()` it will create a global variable.
+* `function foo` has its own trap context, while `foo()` shares them with the current process.
+* `function foo` will set `$0` to foo, while `foo()` will inherit `$0` from the current process.
+
+### Exceptions:
+
+In Bash, `function foo() { ..; }` is allowed, and `function foo` and `foo()` are identical. This warning does not trigger when the shebang is e.g. `#!/bin/bash`. 
+
+### Related resources:
+
+* Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!