Prepend path

mergepaths.pp

class test::mergepaths (
  $envpath = undef,
) {

  $_envpath = $envpath ? {
    undef   => $::path,
    default => join([$envpath, $::path], ':'),
  }

  notify { 'newpath':
    message => $_envpath,
  }
}

shell.sh

[root@puppet2017 /opt/puppetlabs/puppet/modules]# puppet apply -e 'class { "test::mergepaths": }'
Notice: Compiled catalog for puppet2017.3.0.puppetlabs.vm in environment production in 0.04 seconds
Notice: /opt/puppetlabs/puppet/bin:/opt/puppetlabs/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin:/root/bin
Notice: /Stage[main]/Test::Mergepaths/Notify[newpath]/message: defined 'message' as '/opt/puppetlabs/puppet/bin:/opt/puppetlabs/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin:/root/bin'
Notice: Applied catalog in 0.32 seconds

[root@puppet2017 /opt/puppetlabs/puppet/modules]# puppet apply -e 'class { "test::mergepaths": envpath => "/add/this/path", }'
Notice: Compiled catalog for puppet2017.3.0.puppetlabs.vm in environment production in 0.04 seconds
Notice: /add/this/path:/opt/puppetlabs/puppet/bin:/opt/puppetlabs/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin:/root/bin
Notice: /Stage[main]/Test::Mergepaths/Notify[newpath]/message: defined 'message' as '/add/this/path:/opt/puppetlabs/puppet/bin:/opt/puppetlabs/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin:/root/bin'
Notice: Applied catalog in 0.26 seconds