Uninstall all rbenv gems

uninstall_gems.sh

#!/usr/bin/env bash

uninstall() {
  list=`gem list --no-versions`
  for gem in $list; do
    gem uninstall $gem -aIx
  done
  gem list
  gem install bundler
}

#rbenv versions --bare
RBENVPATH=`rbenv root`
echo $RBENVPATH
RUBIES=`ls $RBENVPATH/versions`
for ruby in $RUBIES; do
  echo '---------------------------------------'
  echo $ruby
  rbenv local $ruby
  uninstall
done

Updated solution needed, because of the following header:

*** LOCAL GEMS ***

*** LOCAL GEMS ***

aasm (5.3.0)
abbrev (default: 0.1.1)
ace-rails-ap (4.3)
etc...

Fix:

--no-verbose is what removes the header.
(We may need another fix in the future if things change again)

#!/bin/bash

gem_remove() {
  gem list --no-versions --no-verbose | xargs gem uninstall -aIx
  gem list
}

gem_remove_all() {
  #rbenv versions --bare
  RBENVPATH=`rbenv root`
  echo $RBENVPATH
  RUBIES=`ls $RBENVPATH/versions`
  for ruby in $RUBIES; do
    echo '---------------------------------------'
    echo $ruby
    rbenv local $ruby
    gem_remove
  done
}

I don't include gem install bundler at the end.
Many times in Rails, Gemfile.lock will include a specific bundler version, so I prefer to just install that version manually.