multigem.pp

$versions = ['5.3.3', '4.9.0', '2.7.4', '3.6.2', '3.8.5' ]

# ...

if $versions {
  $_versions = $versions.sort.reverse.join(', ')
  $_packages = $versions.map |$version| {
    "puppet:${version}"
  }.join(' ')

  exec { "gem install ${_packages} --bindir /tmp --no-document":
    path     => '/usr/local/bin:/usr/bin:/bin:/opt/puppetlabs/bin',
    unless   => "[[ \"$(gem list ^puppet$ | tail -1)\" == \"puppet (${_versions})\" ]]",
    provider => shell,
  }
}