Rework sourcing of .bashrc

.profile

@@ -43,11 +43,11 @@ export GCC_COLORS=auto
 	ssh-add "$HOME/.ssh/admin@homeserver" >/dev/null 2>&1
 }
 
-# if executing interactively
-# execute .bashrc in the current login context
-case $- in
-*i*) ;;
-*) return ;;
-esac
-[ -z "${PS1-}" ] && return
-[ -f "$HOME/.bashrc" ] && . "$HOME/.bashrc"
+#shellcheck disable=SC1091
+# Source ~/.bashrc, when in interactive mode, but not POSIX/sh mode.
+[ "$BASH" ] &&
+	[ "$PS1" ] &&
+	[ -z "$POSIXLY_CORRECT" ] &&
+	[ "${0#-}" != 'sh' ] &&
+	[ -r "$HOME/.bashrc" ] &&
+	. "$HOME/.bashrc"