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z/VM Module 8: CMS Pipelines. Objectives. Describe the fundamental concepts behind CMS Pipelines Explain what device drivers are and how they work Explain the difference between running the PIPE command from a command prompt and from a REXX EXEC
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Objectives • Describe the fundamental concepts behind CMS Pipelines • Explain what device drivers are and how they work • Explain the difference between running the PIPE command from a command prompt and from a REXX EXEC • Describe filters and how they are used within a CMS Pipeline
Objectives continued • Describe how to use the LOCATE and FIND commands to select records • Explain how to create your own filters using REXX • Show how to use pipelines in EXECs and XEDIT macros in different subcommand environments • Describe the commands needed to create a SPOOL file to hold information
Objectives continued • List the commands needed to read information from a SPOOL file • Describe the CP commands that control the virtual reader • Describe what multistream pipelining is and how to use it
The PIPE Command • PIPE:
Some Popular Device Drivers • The console filter reads from the terminal and types on it; for example: • Pipe console | console • CONSOLE can provide two functions: • Read input, when it is first in a pipeline specification • Type the input it gets, when it is not first • A device driver that writes to a device also writes the output to the pipeline.
Some Popular Device Drivers, continued • Reading and writing disk files: • ‘<‘ to read a file • ‘>’ to create or replace a file • ‘>>’ to append to or create a file • LITERAL: • A literal creates a record with the argument string and writes to a pipeline • Combining input drivers: • This allows the programmer to create a file at one location and append, copy, or overwrite the file later in the pipeline.
Using the PIPE Command and Other Commands • The PIPE command is not part of the pipeline itself, therefore it is not considered a stage. • In the reading and writing example, the left-hand stage reads the file from disk and the right-hand stage appends to the file specified. • In the second example, we use the CONSOLE command to print the file to the screen. This is helpful when you want to see the file quickly.
Filters • A filter is an application in a pipeline that takes its input from the stage to the left and passes its output to the stage to the right. • The filters that are supplied with CMS Pipelines have many general-use functions. • A function can be anything.
Filters: XLATE - Change Characters XLATE: • This filter translates data passing through the pipeline on a character-by-character basis. • Some sample pipes: • Pipe literal ABCDEFG | xlate 1-* lower | console • Pipe literal abcdefghi | xlate c-g = e e | console • This filter is also capable of altering multiple characters and character ranges in a single stage or pipe.
Filters: XLATE - Change Characters XLATE: /* Replace “%” with “.” and */ /* Replace “!” with “0” and */ /* Replace “4” with “0” and */ /* Replace “+” with “-” */ “Pipe Literal Don’t forget that (2+2) / 10 = 40%! |”, ‘Xlate 1-* % . ! 0 4 0 + - |’, ‘Console’ ________________________________________ Don’t forget that (2-2) / 10 = 00.0
Making Records Longer or Shorter • CHOP truncates each record after a column. • PAD fills each record to the specified length with a pad character (the default is a blank). • Example: • Pipe disk Unknown Data | pad 256 | chop 256 | > Demo output A • You can combine chop and pad to create fixed format records. • Strip removes blanks from both the beginning and the end of records.
Reformat Records • SPLIT creates an output record for each blank-delimited word in its input record. • JOIN creates a single record from one or more input records. • FBLOCK reformats the input stream to fixed length records.
Buffer Filters • A filter that buffers a file reads all input records before writing output records. • The SORT filter must buffer the file by the nature of its processing. • Use BUFFER when a file must be buffered but not reordered. • Examples: • Pipe Disk INPUT FILE | Split | Sort unique | Console • Pipe console | buffer | stack
Discarding and Keeping Records • Use TAKE and DROP to retain or discard a specified number of records from the beginning or end of the file. • TAKE and DROP make it easy to select records based on their position in the file. • The DROP filter is the converse of TAKE, which allows you to delete the first or last n lines.
Writing REXX Filters • There are two types of REXX programs you can write to run in a pipeline: • One reads input records and writes output records, just like all other programs • The other kind is a subroutine pipeline • The REXX program ‘COPY REXX’ copies its input to the output. It can be used as a prototype for more complex filters.
Pipeline Input and Output in a REXX Program • Two of the most important REXX interface commands are READ and WRITE. • The READTO command has a single argument: the name of the variable you wish to be set to the contents of the next input record. • The OUTPUT command is followed by the data you wish to write; you can compute the output data as a REXX expression or you can write a literal.
Using Pipelines in EXECs and XEDIT Macros continued • VAR handles the special case where you want to read and write a single record with the contents of a REXX variable. • When you run the pipeline shown in the notes, the SCRIPT macro reads a line from the stack and inserts it in the document.
Getting Information about Files • STATE and STATEW provide information about selected files. • STATEW only searches minidisks that are accessed in write mode. • The underlying CMS commands allow asterisks for components of a file name, so you can find the first occurrence of a certain type of file.
Subcommand Environments • There can be several subcommand environments active in your session, such as XEDIT, CMS, and ISPF. • The SUBCOM device driver takes as an argument the name of a subcommand environment, which is used for execution and displaying output.
More REXX Interface Commands • CALLPIPE replaces a stage with a pipeline. • The asterisk followed by a colon, which seems to be a stage by itself, is called a connector. • Connectors are the magic that tells CALLPIPE to take the input and output for the stage issuing the command and connect it to a new pipeline. • CALLPIPE returns when all stages of the new pipeline have completed.
Output Device Driver - Creating a SPOOL File • Three device drivers write lines on unit record devices. • Some output device drivers include: • Printmc For a virtual printer • Punch For a virtual punch • Uro Can write to either device • For complete control, you must issue SPOOL, TAG, and CLOSE commands as required.
Unit Record Input - Reader SPOOL Files • SPOOL files in your virtual reader can come from several sources that have different formats; for example: • virtual card punch • virtual printer • CP-generated SPOOL files, such as a VMDUMP • read from a real card reader • A reader reads a file and writes a line to the pipeline for each CCW in the SPOOL file.
CP Commands to Control the Virtual Reader • The characteristics of a virtual reader can be set by the CP command SPOOL, which can control: • CLASS • NOCOUNT & CONT • NOHOLD & HOLD • A printer file is probably easier to handle than a punch file because you often want to retain the carriage control provided by the printer. • Punch files are more complicated because a punch file usually has more than plain data records.
Conclusion • Each section of this module deals with an aspect of CMS Pipelines. • The pipeline concepts discussed were: • Device drivers • Filters • Selecting records • Writing REXX filters • Using pipeline macros • Unit record input and output • These topics help students learn the necessary elements for creating their own pipelines.
Glossary CHOP: – truncates each record after a column FBLOCK: – reformats the input stream to fixed length records Filter: – a stage in a pipeline that takes its input from the stage to the left of it and passes its output to the stage to the right of it JOIN: – creates a single record from one or more input records
Glossary LOCATE: – writes only the records that contain a specific string NLOCATE: – writes all records that do not contain the string specified as the argument PAD: – fills each record to the specified length with a pad character Pipeline: – a series of programs that data passes through. SPLIT: – creates an output record for each blank-delimited word in its input records
Glossary SORT: – orders the input in ascending or descending order UNPACK: – converts a file from the packed format supported by COPYFILE and XEDIT to plain records VAR: – handles the special case where you want to read and write a single record with the contents of a REXX variable XLATE: – translates data passing through the pipeline on a character by character basis
References Hartmann, J., L. Kraines, and J. Lynn. CMS Pipelines Tutorial. GG66-3158-00, February 1990. IBM. z/VM: CMS Pipelines User’s Guide. SC24-5970-00, February 2001. IBM. z/VM: CMS Command and Utility Reference. SC24-6010-02, May 2002.
