Updated SC3044 (markdown)

SC3044.md

@@ -1 +1,60 @@
-In POSIX sh, 'declare' is undefined.
+## In POSIX sh, `declare` is undefined.
+
+### Problematic code:
+
+```sh
+#!/bin/sh
+declare var="value"
+```
+
+or
+
+```sh
+#!/bin/sh
+declare -r readonly
+```
+
+or
+
+```sh
+#!/bin/sh
+declare ...
+```
+
+### Correct code:
+
+If assigning a simple variable outside of a function, skip `declare` all together:
+
+```sh
+var=value
+```
+
+If declaring a variable read-only:
+```
+var=value
+readonly var
+```
+
+If you are unable to find a suitable replacement, consider switching to a shell that supports `declare`:
+
+```sh
+#!/bin/bash
+declare ...
+```
+
+Indexed arrays, associative arrays, local variables, namerefs, and integer variables are not supported in POSIX sh.
+
+### Rationale:
+
+The `declare` command is non-standard, and most of its functionality is not available across shells.
+
+Either find a POSIX replacement, or switch to a shell that is guaranteed to support them.
+
+
+### Exceptions:
+
+If your `declare` command is guarded by a check of the shell version, such as inspecting `$BASH_VERSION`, you can ignore this message.
+
+### Related resources:
+
+* Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!