When invoked without further parameters, this command lists the names of all short pseudonym columns that refer to a Castor study. This means that the values in the listed columns are the Castor record IDs for the corresponding participant.
The command accepts an optional `--imported-only` switch. If specified, the command outputs only those columns that are processed when importing data from Castor into PEP. These are the column names that can be passed to the [`castor list-import-columns`](#castor-list-import-columns) and [`castor create-import-columns`](castor-create-import-columns) subcommands.
The command accepts an optional `--imported-only` switch. If specified, the command outputs only those columns that are processed when importing data from Castor into PEP. These are the column names that can be passed to the `--sp-column` switch of the [`castor list-import-columns`](#castor-list-import-columns) and [`castor create-import-columns`](castor-create-import-columns) subcommands.
