checking whether a package is installed

[Aaron Maxwell <amaxwell@phy.ucsf.edu>]

Is there a quick, elegant way to check if a particular package is
installed?

Right now I just use dpkg -L.  E.g.,

yomama[26]% dpkg -L msword
Package `msword' is not installed.

Use dpkg --info (= dpkg-deb --info) to examine archive files,
and dpkg --contents (= dpkg-deb --contents) to list their contents.
yomama[27]% dpkg -L emacs20 | wc -l
    904
yomama[28]% 

This is more what I have in mind:
yomama[34]% dpkg -s junkbuster | grep "^Status:"
Status: install ok installed
yomama[35]% 

... just a lotta keystrokes.  i can make an alias/shell function, but it's
good to have something portable when helping others debug their system,
etc. 

Aaron