macOS command-line tools you might not know about

Needs to mention afplay for playing audio! You can easily use this to make a command-line MP3 player.

Others have mentioned the “say” utility for speech synthesis. There is a lot you can do with it, it supports the TUNE format, which allows you to "shape the overall melody and timing of an utterance... for example ... to make an utterance sound as if it is spoken with emotion".

See: Apple's Speech Synthesis Programming Guide, https://josh8.com/blog/img/speech-synthesis.pdf

I also wrote more about this here: https://josh8.com/blog/commandline-audio-mac.html