I wrote a lot for my own band and that was probably the best way to get into the business and get to know the right people. Our first album was released in 2004 and people still buy it (word of mouth) so I'm still getting royalties. Lately, I've been writing for other artists as well but you never know if they pick your song and when they do, whether it picks up or not. So luck is a huge factor.

It's not something you pick up just like that. I've been making music as long as I've been programming (about 27 years). So take this "passive income" and divide it by all those hours spent. You'll get something close to zero.

There are books on the topic. I recommend "Tunesmith" by Jimmy Webb. It's about the art and the industry.

On another note, it's really hard for me to bring the two things together. I could program audio software but that's programming, hardly any "art" involved. Lately, I've been making music for computer games but that's just the art, no technical knowledge required. As long as I can think, it's been either/or.

I'm actually that "rockstar programmer". ;)