If you want to get rid of duplicate lines from a file or pipe, use
sort -uor
sort | uniq
For example, maybe you're searching for another front-end to
libpurple, the library underneath
pidgin. You try to use
apt-cache rdepends but find the output is cluttered with
duplicate entries (bug #335925).
$ apt-cache rdepends libpurple0 | tail -n +3 | sort finch finch libpurple-bin libpurple-bin libpurple-dev libpurple-dev msn-pecan pidgin pidgin pidgin-dbg pidgin-dbg pidgin-facebookchat pidgin-librvp pidgin-mpris pidgin-nateon pidgin-plugin-pack pidgin-privacy-please pidgin-privacy-please pidgin-sipe telepathy-haze telepathy-haze
Note that I've trimmed off the header (with tail) and sorted the
list (with sort) here to make this more obvious.
Using the above tip to see only unique lines, you can easily work around this bug:
$ apt-cache rdepends libpurple0 | tail -n +3 | sort -u finch libpurple-bin libpurple-dev msn-pecan pidgin pidgin-dbg pidgin-facebookchat pidgin-librvp pidgin-mpris pidgin-nateon pidgin-plugin-pack pidgin-privacy-please pidgin-sipe telepathy-haze