This chapter presents HTCondor’s ClassAd mechanism in three parts.

The first part may be of interest to advanced job submitters as well as HTCondor administrators: it describes how to write ClassAds and ClassAd expressions, including details of the ClassAd language syntax, evaluation semantics, and its built-in functions.

The second part is likely only of interest to HTCondor administrators: it describes the generic mechanism provided by HTCondor to transform ClassAds, as used in the schedd and the job routers, and as available via a command-line tool.

The third part describes how to format ClassAds for printing from command-line tools like condor_q, condor_history, and condor_status. Advanced users may specify their own custom formats, or adminstrators may set custom defaults.