Created SC2312 (markdown)

SC2312.md

@@ -0,0 +1,37 @@
+## Consider invoking this command separately to avoid masking its return value (or use '|| true' to ignore).
+
+This is an optional suggestion enabled with `shellcheck -o check-extra-masked-returns` or `enable=check-extra-masked-returns` in a `# shellcheck` directive or `.shellcheckrc`.
+
+### Problematic code:
+
+```sh
+set -e
+cd "$(get_chroot_dir)/etc"
+tar xf "$config"
+```
+
+### Correct code:
+
+```sh
+set -e
+dir="$(get_chroot_dir)"
+cd "$dir/etc"
+tar xf "$config"
+```
+### Rationale:
+
+In the problematic example, the exit code for `get_chroot_dir` is ignored because it is used in a command substitution in the argument of another command.
+
+If the command shows `error: Can't determine chroot` and exits with failure without outputting a directory, then the command being run will be `cd "/etc"` and the script will proceed to overwrite the host system's configuration.
+
+By assigning it to a variable first, the exit code of the command will propagate into the exit code of the assignment, so that it can be checked explicitly with `if` or implicitly with `set -e`.
+
+### Exceptions:
+
+If you don't care about the command's exit status, or already handle it through a side channel like `<(cmd; echo $? > status)`, then you can either [[ignore]] the suggestion with a directive, or use `|| true`  (or `|| :`) to suppress it.
+
+Note that this suggestion is optional, and only shows up when explicitly enabled in the script, on the command line, or in a `.shellcheckrc`.
+
+### Related resources:
+
+* Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!