If you gem install --user-install bcat, the gems will get installed under your
user's home directory (typically ~/.gem) instead of the default RubyGems
install path.
rbenv, however, doesn't know how to discover the binstubs created this way and won't be aware of them during the rehash or execution phase.
This plugin adds support for $GEM_HOME environment variable and for searching
executables inside ~/.gem/RUBY_ENGINE/RUBY_VERSION/bin directory for the
current version when executing a command.