Coming at this from a web perspective, here's some admin tools I've written in Perl which I use frequently from the command-line. Feel free to use, borrow, modify (or criticise :-)

WebConf: grep stuff out of the apache, samba, passwd and group files and the like...
http://webdev.co.nz/Perl/WebConf

MetaGeta: read STDIN for a list of HTML filenames, each of which is parsed looking for meta-data and URLs...
http://webdev.co.nz/Perl/MetaGeta