Two types of events cause the execution of a CLIST to halt prematurely: attention interrupts and errors. The CLIST language provides two statements that enable you to code routines to handle attention interrupts and errors. They are ATTN and ERROR. The ATTN statement is described in Writing attention routines. The ERROR statement is described in Writing error routines.

An attention interrupt occurs when the user presses the attention key (typically PA1 or ATTN) on the terminal keyboard. The user may enter an attention interrupt for any number of reasons, such as to terminate an infinite loop or to end the CLIST. The user cannot enter an attention interrupt when a CLIST error routine is in execution as a result of a CLIST-invoked command processor abend or before a TSO/E command is executed within the CLIST. Any attention interruption received while a command abend is in progress is ignored.

An error can occur for any number of reasons, such as a numeric value that exceeds 2³¹-1, an end-of-file condition, or a non-zero return code from a TSO/E command.