SoX harp - simplest cross-platform musical instrument in a few lines of Bash (depends on SoX)

soxharp.sh

#!/bin/bash

function idx() {
  local t=${1%%$2*}
  [[ "$1" == "$t" ]] && echo "-1" || echo ${#t}
}

oct=0

while IFS= read -r -s -n1 i; do
  [[ "$i" == "a" ]] && (( oct > -3 )) && oct=$((oct - 1)) && echo "Octave: $((oct + 3))"
  [[ "$i" == "1" ]] && (( oct < 3 )) && oct=$((oct + 1)) && echo "Octave: $((oct + 3))"
  noteIdx=$(idx 'zsxdcvgbhnjmq2w3er5t6y7ui9o0p[=]' "$i")
  (( noteIdx > -1 )) && play -q -n synth 3 pluck %$(( noteIdx - 12 + 12 * oct )) &
done

Pretty dang cool!