The mainframe and it’s scripting language is a weird beast. Here’s a sample of the scripting language

[sourcecode language=”jcl”]
//LZIOTEST JOB
//A EXEC PGM=IOTEST
//SYSOUT DD SYSOUT=*
//*SYSPRINT DD SYSOUT=*
//SYSPRINT DD DSN=PJOOT.OUT6,DISP=(MOD,KEEP,KEEP),
// DCB=(DSORG=PS,LRECL=80,RECFM=FB,BLKSIZE=800)
[/sourcecode]

When I see this, my gut feeling is to ignore it all, since it looks like a comment. The comments are actually the //* lines, so that is equivalent to:

[sourcecode language=”jcl”]
//LZIOTEST JOB
//A EXEC PGM=IOTEST
//SYSOUT DD SYSOUT=*
//SYSPRINT DD DSN=PJOOT.OUT6,DISP=(MOD,KEEP,KEEP),
// DCB=(DSORG=PS,LRECL=80,RECFM=FB,BLKSIZE=800)
[/sourcecode]

If I understand things properly, the commands in this particular JCL are:

  • JOB (with parameter value LZIOTEST, that identifies the job output in the spool reader)
  • EXEC (with parameter A, which I believe is a step name), and a specification of what to execute for that step (my IOTEST code in this case).
  • DD (define an alias for a file (called a DATASET in mainframe-ese)

The SYSPRINT line associates a DDNAME “SYSPRINT” with a file (i.e. a DATASET) named PJOOT.OUT6. Creating a file seems very painful to do, requiring specification of blocksize, filetype (DSORG), record length, record format (Fixed Blocked in this case), and a DISPosition (whether to create/modify/access-shared/…, and what action to take if the JCL script succeeds or fails). Once that file is created it can then accessed by DDNAME in fopen (i.e. fopen( “DD:SYSPRINT”, …).  I have the feeling that REXX, COBOL, AND PL/1 operate on the DDNAME exclusively, and don’t require it to be prefixed with DD: as the Z/OS C/C++ runtime docs for fopen suggest.

Another oddity with JCL is that it appears to have an 80 character line limitation.  For example, the following produces JCL syntax errors.

[sourcecode language=”jcl”]
//SYSPRINT DD DSN=PJOOT.OUT6,DISP=(MOD,KEEP,KEEP),DCB=(DSORG=PS,LRECL=80,RECFM=FB,BLKSIZE=800)
[/sourcecode]

A trailing comma appears to be the required continuation character.  I don’t know if the indenting I used for DCB= matters, but suspect not.