Created SC3047 (markdown)

SC3047.md

@@ -0,0 +1,39 @@
+## In POSIX sh, trapping ERR is undefined.
+
+(or "In dash, ... is not supported." when using `dash`)
+
+Also applies to RETURN and DEBUG.
+
+### Problematic code:
+
+```sh
+#!/bin/sh
+trap 'Command failed with $?' ERR
+```
+
+### Correct code:
+
+Switch to a shell like `ksh` or `bash` that *does* support the kind of trap you want:
+
+```sh
+#!/bin/bash
+trap 'Command failed with $?' ERR
+```
+
+Otherwise, rewrite the script to not rely on the trap.
+
+### Rationale:
+
+You are trying to install a trap that is not supported by your current shell (`dash` or POSIX `sh`). There is no simple replacement. The script should be rewritten to avoid depending on the trap, or simply be run with a shell that supports it.
+
+### Exceptions:
+
+If you only intend to target shells that supports this feature, you can change
+the shebang to a shell that guarantees support, or [[ignore]] this warning.
+
+You can use `# shellcheck disable=SC3000-SC4000` to ignore all such compatibility
+warnings.
+
+### Related resources:
+
+* Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!