I started playing bass a while ago, and now I am getting into the music theory part. Since I got tired of figuring out the keys/modes myself, I wrote some perl to do it.

The scripts takes two command line arguments, the key and then the mode. If the key is not specified, C is assumed, and if the mode is not specified, major is assumed. See the source for valid keys.

Update: I fixed a bug in the notes array (had "G G", instead of "G G#"). Thanks for the msg jeffa.
Update Again: I fixed the bug where invalid keys/modes weren't recognized.
Yet Another Update: Added ionian (instead of just "major").

Things that still need to be fixed:

• Ouput flats (b). See the first comment below. I have no idea how to do this properly, as saying something like A# or Bb is just "known", there aren't any progmatic rules for it.
• Recognize flats on the command line. el-moe suggested adding "rocker keys", which have flats (Ab, Bb, Eb, Gb).
  Maybe I'll fix it when I get the time. Our maybe one of you could do it ;-).

#!/usr/bin/perl

$key = uc(shift || "C");
$mode = lc(shift || "major");

@notes = qw(A A# B C C# D D# E F F# G G# A A# B C C# D D# E F F# G G#)
+;
%modes = ("major", -1, "ionian", -1, "dorian", 0, "phrygian", 1, "lydi
+an", 2, 
          "mixolydian", 3, "aeolian", 4, "locrian", 5);
@steps = qw(2 2 1 2 2 2 1);

$notematch = join "|", @notes;
if (($key !~ /($notematch)/) || !(exists $modes{$mode})) {die "Invalid
+ key or mode!\n"}


while ($notes[0] ne $key) {
       push(@notes, shift(@notes));
}

for (0 .. $modes{"$mode"}) {
       push(@steps, shift(@steps));
}

unshift(@steps, 0);

foreach $i (@steps) {
       $index += $i;
       print $notes[$index] . " ";
}
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