The isql utility is a command-line Interactive SQL utility that uses the Adaptive Server Enterprise Open Client API. isql is functionally identical to the iqisql utility.
For syntax and parameters, see the Adaptive Server Enterprise documentation: Adaptive Server Enterprise 15.5 > Utility Guide > Utility Commands Reference > isql.
Neither isql nor iqisql let you create user-defined database options. If you need to add your own database options, use the dbisql Interactive SQL utility instead.