Using the (extended) implicit form of the EXEC command

When using the implicit form of the EXEC command, TSO/E finds the REXX exec or CLIST as follows.

Table 1 lists the search order of the user-, application-, and system-level libraries. Also shown are the ddnames associated with each library level. These ddnames can be allocated either dynamically by the ALLOCATE command or included as part of a logon procedure.

Table 1. Library search order
Search order	Library level		Associated ddname
1.	User	REXX exec	SYSUEXEC
2.	User	CLIST	SYSUPROC
3.	Application	REXX exec	Define with FILE or DATASET operand
4.	Application	CLIST	Define with FILE or DATASET operand
5.	System	REXX exec	SYSEXEC (installation can define this ddname)
6.	System	CLIST	SYSPROC

With the default settings that TSO/E provides, and before an ALTLIB command is invoked, TSO/E searches the system EXEC library (default ddname SYSEXEC) first, followed by the system CLIST library (ddname SYSPROC). Note that your system programmer can change this by

Defining an alternate ddname of SYSEXEC
Indicating that TSO/E is not to search the system-level exec ddname of SYSEXEC. Then only the system-level CLIST (SYSPROC) is searched.

You can alter the default library search order by using either the ALTLIB command or the EXECUTIL command.

Use EXECUTIL to indicate that the system-level exec ddname is to be searched for the duration of the current REXX language processor environment.
Use ALTLIB to indicate that the system-level exec ddname is to be searched for the duration of the current application. ALTLIB always overrides EXECUTIL within an application.

Use ALTLIB DISPLAY to see which libraries are being searched for.

The following example uses the implicit form of the EXEC command. It shows how the procedure is run. In this example, assume that the TSO/E prefix is ‘slk27’.