For some reason,
opkg, the package manager of OpenWRT, has a function to list all upgradable packages, but none to upgrade them all – you need to type each one in by hand.
Or you do it like this:
opkg list-upgradable | cut -d " " -f 1 | xargs opkg upgrade
As usual, just paste the three lines of script above into a plain text file and make it executable with
chmod u+x <filename>.
Hope this can help some people out there! 🙂