List of (activated) fonts with shell command in os x
I know that this is quite an old post, but I just stumbled upon it from Google while searching for something similar (mostly just wanting to list active fonts via Terminal.) I ended up remembering that activated fonts are listed in System Information which can be pulled from the system_profiler command.
That being said here's the command to pull font information from system_profiler:

system_profiler SPFontsDataType


That's it. It should return a huge list of font data in the format of:

Fonts:

Arial Narrow.ttf:

  Kind: TrueType
  Valid: Yes
  Enabled: Yes
  Location: /Library/Fonts/Arial Narrow.ttf
  Typefaces:
    ArialNarrow:
      Full Name: Arial Narrow
      Family: Arial Narrow
      Style: Regular
      Version: Version 2.38.1x
      Vendor: The Monotype Corporation
      Unique Name: Arial Narrow Regular : 2007
      Designer: Robin Nicholas, Patricia Saunders
      Copyright: © 2007 The Monotype Corporation. All Rights Reserved.
      Trademark: Arial is a trademark of The Monotype Corporation in the United States and/or other countries.
      Description: Monotype Drawing Office 1982. A contemporary sans serif design, Arial contains more humanist characteristics than many of its predecessors and as such is more in tune with the mood of the last decades of the twentieth century. The overall treatment of curves is softer and fuller than in most industrial-style sans serif faces. Terminal strokes are cut on the diagonal which helps to give the face a less mechanical appearance. Arial is an extremely versatile family of typefaces which can be used with equal success for text setting in reports, presentations, magazines etc, and for display use in newspapers, advertising and promotions.
      Outline: Yes
      Valid: Yes
      Enabled: Yes
      Duplicate: No
      Copy Protected: No
      Embeddable: Yes


which you should be able to grep and manipulate as you'd like.