This was grabbed off of rec.music.makers.guitar, posted by Andrew Rogers.
From the post:

  'Anyway, this is
  a Unix/PostScript hack to generate a one-octave fretboard diagram for any
  fretted string instrument (OK, any chromatic one - no dulcimers) in any
  tuning; you supply the pitches of the open strings (command line arguments)
  and it does the rest.  Default is guitar in standard tuning.

  (If you have PostScript but not Unix, blow away all the Unixisms and edit
  your choice of open string pitches directly into the

          /openstrings [ $openstrings ] def

  line, following the syntax in the preceding comment.)'

To make an executable file from the shell script, type:
  chmod +x <filename>

Then just type <filename> to run it, and pipe the output to a
Postscript printer or viewer.

The output is a 12-fret fretboard with the notes of each string printed
on each fret.  This could be useful when dealing with alternate tunings,
and it can accommodate non-guitar instruments (like mandolin, bass, etc.).