Equery

equery is a tool to make several common portage operations simpler. Among other operations, it can display package dependencies, metadata, and installed files.

Installation
Install :

Capabilities
To see a list of all equery's capabilities, simply run it without arguments:

Module (b)elongs
List what package  belongs to:

Module (d)epends
List all packages directly depending on udev:

Module (f)iles
List all files installed by ncmpcpp:

Descriptions of other modules and additional command line flags can be found in the equery man page.

Aliases
If you found yourself using equery all the time you could write down a few handy aliases. When using bash you can usually edit the file: