Yeah, I don't think Bourne shell (the original /bin/sh) supports this, and it works many places because the powers-that-be link /bin/sh to /bin/bash or some other advanced Bourne-y shell.
Bash is everywhere, so madmarcel's change would make it more "correct", but you could go the other way too:
Though that is a little line-noise-ish. :-)
Thanks for this, marcusmoller!
You can take it one step further and build it into a single texture (using the 256x32 pngs):
That will create a 1024x736 png with all the sprites. I put up a copy here:
Remember to credit him: