$ spot
 Spotlight CLI.

If a command takes a [path], the results will be restricted to that directory.

apps                      Installed applications.
attr                      Attributes that can be used with "spot <query>".
author <query> [path]     Files from author.
ext <query> [path]        Any files with that extension.
                          $ spot ext pdf ~
file <query> [path]       Find files.
                          $ spot file vimrc ~/dotfiles
group <group|gid> [path]  All files from user.
                          $ spot group $GID /etc
size <rel> <size> [path]  Find all files of a certain size in bytes.
                          Or (k)ilobytes, (m)egabytes, (g)igabytes.
                          $ spot size '>=' 1g ~
text <query> [path]       Find files containing text.
                          $ spot text 'ascii porn' ~
user <user|uid> [path]    All files from user.
                          $ spot user $UID /var

<path>                    Get all attributes for that path.
                          $ spot ~/fancy.gif
<query> [path]            Generic query. Supports any attributes from "spot attr".
                          See link at the bottom for the syntax.
                          $ spot foo
                          $ spot 'kMDItemMusicalGenre == *Metal*' /data/music

The Spotlight query syntax explained:
https://developer.apple.com/library/mac/documentation/Carbon/Conceptual/SpotlightQuery/Concepts/QueryFormat.html

It's also fiendishly easy to add new commands to spot. For adding a command "music", simply add an executable shell script called "spot-music" to your $PATH:

#!/usr/bin/env bash

# The following line is optional and outputs a small reminder,
# if not enough arguments were given to the "music" command.
required $# '<genre>'

mdfind "kMDItemMusicalGenre == $1"

Using this, you can simply list all songs of a certain genre:

$ spot music Metal
$ spot music "Alpine folk music"

You could also change spot-music to take a second optional argument, to restrict the matches to a certain directory:

#!/usr/bin/env bash

required $# '<genre>'

genre=$1
dir=$2

mdfind "kMDItemMusicalGenre == $genre" ${dir:+ -onlyin "$dir"}

Now, you can also use it like this:

$ spot music Metal ~/music