Control a command with a variable or class parameter in Puppet

example.pp

# Run a command saved as a variable:
$desired_command = '/bin/ls -ld /etc'

exec { 'some arbitrary command':
  command => $desired_command,
}

# Run a command inside a class, with a parameter to control the command:

class oracle::setup (
  $someparam,
  $desired_command,
  $someparam,
) {
  # some arbitrary puppet code

  exec { 'setup command':
    command => $desired_command,
  }

  # some more arbitrary puppet code
}