About expression processing

When an expression is entered (freeform or “by field”), File Manager evaluates the expression to see if it can be processed internally or if it must be passed to REXX.

REXX stands for the REstructured eXtended eXecutor language. REXX is a general purpose programming language, similar to PL/I. It includes extensive parsing capabilities for character manipulation, extensive mathematical capabilities, and numerous built-in functions that perform various processing, searching, and comparison functions.

REXX programs are usually run by a language processor (interpreter). That is, the program is run statement-by-statement, without first being translated to another form (compiled). Because of the interpretive nature of REXX, File Manager is able to exploit the power of REXX when processing record identification and record selection criteria.

Although REXX is a powerful and versatile language, coding selection criteria using REXX is straightforward. You do not need to know how to write REXX programs. All you need to know is how to write REXX comparison expressions. File Manager takes care of turning your selection criteria into a REXX program.

Much of the information in this section has been extracted from the z/OS TSO/E REXX Reference and z/OS TSO/E REXX User's Guide. For more detailed information about REXX, refer to those manuals.