IBM TSO/E REXX User Manual

2. At the application and system levels, ALTLIB uses the virtual lookaside facility
(VLF) to provide potential increases in library search speed.
Stacking ALTLIB Requests
On the application level, you can stack up to eight activate requests with the top, or
current, request active. Application-level libraries you define while running an ISPF
application are in effect only while that application has control. When the application
completes, the original application-level libraries are automatically reactivated.
Using ALTLIB with ISPF
Under ISPF, ALTLIB works the same as in line mode TSO/E. However, if you use
ALTLIB under line mode TSO/E and start ISPF, the alternative libraries you
specified under line mode TSO/E are unavailable until ISPF ends.
When you use ALTLIB under ISPF, you can pass the alternative library definitions
from application to application by using ISPEXEC SELECT with the PASSLIB
operand; for example:
ISPEXEC SELECT NEWAPPL(ABC) PASSLIB
The PASSLIB operand passes the ALTLIB definitions to the invoked application.
When the invoked application completes and the invoking application regains
control, the ALTLIB definitions that were passed take effect again, regardless of
whether the invoked application changed them. If you omit the PASSLIB operand,
ALTLIB definitions are not passed to the invoked application.
For more information about writing ISPF applications, see z/OS ISPF Services
Guide.
Examples of the ALTLIB Command
In the following example, an application issues the ALTLIB command to allow
implicit execution of execs in the data set NEW.EXEC, to be searched ahead of
SYSPROC:
ALTLIB ACTIVATE APPLICATION(exec) DATASET(new.exec)
The application could also allow searching for any private execs that the user has
allocated to the file SYSUEXEC or SYSUPROC, with the following command:
ALTLIB ACTIVATE USER(exec)
To display the active libraries in their current search order, use the DISPLAY
operand as follows:
ALTLIB DISPLAY
For more information about the search order EXEC uses for execs and CLISTs, see
z/OS TSO/E Command Reference.
To deactivate searching for a certain level, use the DEACTIVATE operand; for
example, to deactivate searching for execs on the system level (those allocated to
SYSEXEC or SYSPROC), issue:
ALTLIB DEACTIVATE SYSTEM(exec)
And, to reset exec searching back to the system level, issue:
ALTLIB RESET
Specifying Alternative Exec Libraries ...
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z/OS V1R1.0 TSO/E REXX User’s Guide

IBM TSO/E REXX Specifications

General

Brand	IBM
Model	TSO/E REXX
Category	Computer Hardware
Language	English