URL encoding in pure Bash

urlencode.sh

#!/usr/bin/env bash
set -o nounset

while IFS= read -r -n 1 char; do
  case "$char" in
    [-_.~a-zA-Z0-9])
      printf %s "$char"
      ;;
    *)
      printf '%%%02x' "'$char"
      ;;
  esac
done