use strict;

sub chord_progression
{
    # The parameter is the index of the root note in the @notes array
    my $i = shift;
    my @notes = ('C', 'C#/Db', 'D', 'D#/Eb', 'E', 'F', 'F#/Gb',
                 'G', 'G#/Ab', 'A', 'A#/Bb', 'B');
    my @intervals = (0, 2, 4, 5, 7, 9, 11, 12);

    # Create a scale based on the intervals in a major scale
    my @scale = map {$notes[($i + $intervals[$_]) % 12]} (0..7);

    # Create triads.  Increment each note within the scale.
    # All notes in the chord progression fall within the
    # major scale.
    my ($root, $third, $fifth) = (0, 2, 4);
    my @name = ('Maj', 'min', 'min', 'Maj', 'Maj', 'min', 'Dim', 'Maj'
+);
    for (0..7) {
        printf "%6s %3s: %6s, %6s, %6s\n",
               $scale[$root], $name[$_], $scale[$root], 
               $scale[$third], $scale[$fifth];
        $root++;
        $third++;
        $fifth++;
        $root %= 7;
        $third %= 7;
        $fifth %= 7;
    }
    print "\n";
}

# Call the subroutine for each note in the scale
for (0..11)
{
    chord_progression($_);
}
[download]

     C Maj:      C,      E,      G
     D min:      D,      F,      A
     E min:      E,      G,      B
     F Maj:      F,      A,      C
     G Maj:      G,      B,      D
     A min:      A,      C,      E
     B Dim:      B,      D,      F
     C Maj:      C,      E,      G

 C#/Db Maj:  C#/Db,      F,  G#/Ab
 D#/Eb min:  D#/Eb,  F#/Gb, A#, Bb
     F min:      F,  G#/Ab,      C
 F#/Gb Maj:  F#/Gb, A#, Bb,  C#/Db
 G#/Ab Maj:  G#/Ab,      C,  D#/Eb
A#, Bb min: A#, Bb,  C#/Db,      F
     C Dim:      C,  D#/Eb,  F#/Gb
 C#/Db Maj:  C#/Db,      F,  G#/Ab

...