pwfilter (which also includes shdwfilter and grpfilter) is an easy way to filter through passwd, shadow, and group files by ID.
It's meant to be simple, intuitive, and very portable. It should work on just about every form of *nix and in nearly every Bourne shell — with some small caveats. Please see the PORTABILITY file and the BUGS/CORNER CASES section of the manpage for more information.
If you're interested in helping out, just drop me an email or send a pull request. Patches and (constructive) input are always welcome.
Tests are written using sharness. To
run, simply run make test in the tests directory. To test across the
numerous shells supported by pwfilter, use the test_shells.sh script also
located in the tests directory.