If a UDC calls another UDC, the called UDC m ust be de￿ned in the UDC catalog (see below) after the calling UDC unless recursion is speci￿cally enabled.

To activate the UDCs in a UDC ￿le, the ￿le m ust be identi￿ed to MPE/iX as a catalog. Use the :SETCATALOG command to catalog a UDC ￿le. Eac h time you execute :SETCATALOG , the speci￿ed ￿le becomes the only enabled UDC ￿le, unless y ou specify that more ￿les should be appended. An enabled UDC ￿le is frequen tly called a UDC catalog.

Executing :SETCATALOG without any ￿le names disables all UDC catalogs. Y ou must ￿rst disable the UDC catalog to sa ve a new version of a it to the same ￿le name. If y ou do not want to disable the UDC catalog, y ou can save a new version of it under a di￿eren t ￿le name. Executing :SHOWCATALOG shows a list of all UDC catalogs (enabled UDC ￿les) and the UDCs within them.

The ￿le named COMMAND.PUB.SYS contains a table of UDC users and catalogs. Purging or putting a lockword on this ￿le disables all UDCs.

When you use a UDC, catalogs are searc hed for the speci￿ed command name in the follo wing order of catalogs set at:

User level (Us)

Account level (Ac)

System level (Sy)

The order in which UDC catalogs are searc hed within a lev el is determined by the order in which they were speci￿ed in the :SETCATALOG command. Command de￿nitions are sequentially searched for execution in order of appearance in a UDC catalog.

System resources are required to manage UDCs for eac h session in whic h they are enabled. UDCs that are automatically executed at log on cause an increase in the time required to complete the log on. A situation where man y users have several UDC catalogs (enabled UDC ￿les) can have a severe negative impact on system performance.

For detailed information on command ￿les and UDCs, refer to Command Interpreter Access and Variables Programmer's Guide (32650-90011).

Break Mode

When a process is in con trol, it reads user input and acts according to its o wn rules and conventions. It is possible to temporarily in terrupt the process to go bac k to the command interpreter (CI) without exiting the process and ha ving to restart it. When this occurs, the CI is executing in break mode.

Activating the BREAK key interrupts the data comm unication function of the terminal. This can suspend or terminate the process curren tly executing (for example, a subsystem or user program). The program curren tly running is in terrupted, not the actual MPE/iX command that started execution of the program; this command ma y have already completed execution. In break mode, y ou can enter MPE/iX commands and user-de￿ned commands (UDCs). When you press the BREAK key, the colon prompt (:) appears, indicating that y our session is in break mode.

The following MPE/iX commands can be in terrupted by pressing the BREAK k ey. This action aborts the output of the command, not its action:

OVERVIEW 1-21