Not sure if there's any use for it upstream, but I figure I might as well alert you all to an adaption of debootstrap's pkgdetails [1] and the extract functionality of ar [2] into posix shell.
The ar adaption is dead simple; I'm surprised nobody has done it before (or maybe they have, and my cursory searches didn't turn it up).
The pkgdetails adaption was less simple, and while it works (and of course produces the same output as the C and Perl versions, as far as I can tell), it's definitely slower than the other two.
These scripts work well for running debootstrap in a standard Chromium OS environment (no Perl, Python, or build tools), so perhaps the Debian community could find something useful to do with them as well.
-David
[1]
https://github.com/dnschneid/crouton/blob/master/installer/pkgdetails[2]
https://github.com/dnschneid/crouton/blob/master/installer/ar