Identify an acceptable variable name in Puppet.

The choice of $server as an acceptable variable name in Puppet is correct due to the naming conventions established for Puppet variables. In Puppet, variable names must begin with a dollar sign ($) followed by a letter or an underscore. The use of alphanumeric characters and underscores is permitted thereafter, but they cannot start with a digit or contain special characters like dashes.

The variable name $server starts with a letter and follows the conventions appropriately without any invalid characters. This adherence to the rules ensures that the variable can be easily recognized and interpreted by Puppet without any parsing issues.

In contrast, other examples fail to meet naming criteria: $12server begins with a digit, which is not allowed, and $server-name contains a hyphen which is not permitted in variable names. These restrictions are put in place to maintain clarity and avoid conflicts in variable recognition within the Puppet language.