IBM Tivoli NetView for z/OS Programming: Pipes - IBM notice

Introduction and Concepts
Stages
10 Programming: Pipes
It is possible for a connector to be neither first nor last, in which case, the
connector defines both an input and an output for the labeled stage. It is also
possible to use two connectors in a row. This usage connects the output of one
labeled stage to the input of another.
In the following example, the secondary output of LOCATE is connected to the
secondary input of FANIN:
PIPE (END ¬)
| < SOMEMEM
| COLOR YELLOW
| RD: LOCATE /GREEN/
| COLOR GREEN
| BK: FANIN
| CONSOLE ONLY
¬ RD:
| BK:
The PIPE stages in this example are explained in detail in Chapter 2, “Pipeline
Stages and Syntax,” on page 19. For now, understand that < reads data from a data
set member called SOMEMEM, the COLOR stage changes the color of text
presented on the CONSOLE, and FANIN collects data from multiple input streams
and passes the data to a single output stream.
In this pipeline, all the records in the member SOMEMEM are read and given the
color attribute YELLOW. Then, all records containing the word GREEN are colored
green. Records containing the word GREEN flow through the pipeline directly to
the FANIN stage and then to the console. Records that do not contain the word
GREEN flow to the RD: connector from the LOCATE/GREEN/ stage, which
defines the RD: label. Because the BK: connector follows the RD: label, the data
flows from the BK: connector as input to the stage defining it (BK: FANIN).
Stages that Disconnect Streams before Termination
Some stages can disconnect a stream before terminating. An example is the TAKE
stage. The TAKE stage disconnects its primary output as soon as the specified
count is reached. However, if a secondary output stream is defined, the TAKE
stage is not terminated. It continues to pass messages to its secondary output
stream.
The processing of the TAKE stage is important to the following REXX pipeline,
because FANIN will not begin to read its secondary input until its primary input
has disconnected:
’PIPE (NAME REDNAME END ¬)’,
’| < NAMELIST’, /* Read list of names */
’|C: TAKE 12’, /* Hope to get 12 or fewer names */
’|R: FANIN’, /* Bringing names together */
’| $STEM NAMEVAR.’, /* Save names in order FANIN reads */
’| CONSOLE’, /* and display them */
’¬ C:’, /* Pick up excess names from TAKE */
’| COLOR RED’, /* Names past twelfth should be red */
’| R:’ /* give these to FANIN’s secondary */
The first 12 names are displayed on the console in the default color. The remaining
names are displayed in red.
Depending on their function, stages can be grouped into two categories: device
drivers and filters.