[sh] Check if a ruby gem is installed

check_ruby_debug.sh

# gem list -i -e 'debug' -v '>= 1.0.0'
# -i returns true / false
# -e exact match (avoid partial match), could also be a regex e.g. '^debug$'
# -v specify gem version (may also use pessimistic version)

function check_ruby_debug() {
  debug_gem_installed=$(gem list -i -e "debug" -v ">= 1.0.0")
  if [[ $debug_gem_installed = "false" ]]; then
    echo -e "Ruby's debug gem not installed!"
    echo -e "run: gem install debug"
    exit 1
  fi
}