MusicBrainz Picard naming scripts

Tracks with release IDs

$upper(%_extension%)/
$set(_aartist,$substr($if2(%albumartist%,%artist%),0,1))
$if($in(0123456789,%_aartist%),#,$if($not($in(ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz,%_aartist%)),#,$upper(%_aartist%)))
/$if2(%albumartist%,%artist%) (%musicbrainz_albumartistid%)/
%album% (%musicbrainz_albumid%)/
$if($gt(%totaldiscs%,1),$if($gt(%totaldiscs%,9),$num(%discnumber%,2),%discnumber%)-,)$num(%tracknumber%,2) - %title%

Line by line:
Extension/
Set variable to first letter of artist.
First letter - A-Z, or fall back to # for numbers, symbols and other scripts/
Album artist if available, fall back to artist (MusicBrainz Artist ID)/
Album title (MusicBrainz Album ID)/
For multiple disc releases, use 1-01

Example result: FLAC/P/PNAU (b04df404-eefa-4ae4-9f3e-ba220d9dce16)/Changa (90009c4b-e930-41f7-b221-d54daa15a71b)/03 - Go Bang.flac

Tracks without release IDs

$upper(%_extension%)/
$set(_aartist,$substr($if2(%albumartist%,%artist%),0,1))
$if($in(0123456789,%_aartist%),#,$if($not($in(ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz,%_aartist%)),#,$upper(%_aartist%)))
/$if2(%albumartist%,%artist%)/
%album%/
$if($gt(%totaldiscs%,1),$if($gt(%totaldiscs%,9),$num(%discnumber%,2),%discnumber%)-,)$num(%tracknumber%,2) - %title%

Example result: FLAC/P/PNAU/Changa/03 - Go Bang.flac