If you are adding customizations to your zshrc, such as adding auto completion for a certain gem, you want to make sure that the gem is installed before performing any action.
gem list [gemname] -i command returns a boolean representing whether a gem is installed or not.
if `gem list lunchy -i`; then echo "Lunchy gem is installed!"; # do some configurtion here fi
If you wish to be more granular you can check whether a specific version is installed by adding the
--version [version] flag.
if `gem list lunchy -i --version 0.10.4`; then echo "Lunchy v0.10.4 is installed!"; # do some configurtion here fi