Tailor and run jcl programmatically using rexx - mainframe

Question

Monthly, I need to run a set of JCLs. These JCLs has some hardcoded parameters that I need to be changed every month (eg: the year/month of the source file).
On the other hand, these JCL need to be run for many source files:
LEA.D.1804.L03
LEA.D.1804.L04
LEA.D.1804.L05
and so on..
Here is an excerpt of a JCL:
//*---------------------------------------------------------------------
//STEP01 EXEC PGM=OSGENER
//*---------------------------------------------------------------------
//SYSPRINT DD SYSOUT=T
//*
//SYSUT1 DD DSN=LEA.D.1804.L03,DISP=SHR
//*
//SYSUT2 DD DSN=LEA.L03.DAT,UNIT=SYSDA,DISP=(,PASS),
// DCB=(RECFM=FB,LRECL=135,BLKSIZE=0),SPACE=(CYL,16,RLSE)
//SYSIN DD *
RCOUT 4,,'016011'
RCOUT 4,,'016012'
RCOUT 4,,'016021'
COPY
I believe (and hope) that there must be some way to use params instead of these harcoded values.
I think that I could use rexx to call these JCLs programmatically, looping the source files.
First, is this possible?
How do I do to use vars/params in my JCLs instead of harcoded values?
(I also know that there is something called file tailoring but I can't understand how I should use it)
I come from PHP, Java, Javascript and those kind of langs stacks. Please be as clear and explicit as possible.
Thanks!

Answer 1

I'm going to presume that file tailoring isn't a requirement because it isn't necessary in order to solve your problem.
My recommendation would be to code a procedure, cataloged or in-stream, and then execute it with your different parameters.
//MYPROC01 YY=SUPPLYTWODIGITYEAR,
// MM=SUPPLYTWODIGITMONTH,
// LLQ=SUPPLYLOWLEVELQUALIFIER
//*
//*---------------------------------------------------------------------
//STEP01 EXEC PGM=OSGENER
//*---------------------------------------------------------------------
//SYSPRINT DD SYSOUT=T
//*
//SYSUT1 DD DSN=LEA.D.&YY.&MM..&LLQ,DISP=SHR
//*
//SYSUT2 DD DSN=LEA.&LLQ..DAT,UNIT=SYSDA,DISP=(,PASS),
// DCB=(RECFM=FB,LRECL=135,BLKSIZE=0),SPACE=(CYL,16,RLSE)
//SYSIN DD *
RCOUT 4,,'016011'
RCOUT 4,,'016012'
RCOUT 4,,'016021'
COPY
//*
// PEND
//*
//LLQ3 EXEC PROC=MYPROC01,YY=&LYR2,MM=&MON,LLQ=L03
//LLQ4 EXEC PROC=MYPROC01,YY=&LYR2,MM=&MON,LLQ=L04
//LLQ5 EXEC PROC=MYPROC01,YY=&LYR2,MM=&MON,LLQ=L05
//*
this is just freehand, no guarantees I haven't introduced a typo
The &LYR2 and &MON dynamic system symbols were new with z/OS 2.3, and procedures gained the capability of housing in-stream data a couple of releases prior to that.
Absent the ability to use system symbolics, I suggest talking to whomever is responsible for scheduling jobs in your shop. Most mainframe shops have a job scheduling package and these tend to have powerful date manipulation capabilities.

Answer 2

In our site, we do have some jobs which run in Monthly basis and the only parameter which keeps changing is the Month & year (in MMMYY format ex: APR18). The jobs are scheduled in Control-M. The MMM & YY variables to be used in the JCL symbolic overrides are set by Control-M based on current month/year.
%%IF %%OMONTH EQ 01
%%SET %%MON = JAN
%%GOTO ENDIT
%%ENDIF
%%IF %%OMONTH EQ 02
%%SET %%MON = FEB
%%GOTO ENDIT
%%ENDIF
%%IF %%OMONTH EQ 03
%%SET %%MON = MAR
%%GOTO ENDIT
%%ENDIF
%%IF %%OMONTH EQ 04
%%SET %%MON = APR
%%GOTO ENDIT
%%ENDIF
%%IF %%OMONTH EQ 05
%%SET %%MON = MAY
%%GOTO ENDIT
%%ENDIF
%%IF %%OMONTH EQ 06
%%SET %%MON = JUN
%%GOTO ENDIT
%%ENDIF
%%IF %%OMONTH EQ 07
%%SET %%MON = JUL
%%GOTO ENDIT
%%ENDIF
%%IF %%OMONTH EQ 08
%%SET %%MON = AUG
%%GOTO ENDIT
%%ENDIF
%%IF %%OMONTH EQ 09
%%SET %%MON = SEP
%%GOTO ENDIT
%%ENDIF
%%IF %%OMONTH EQ 10
%%SET %%MON = OCT
%%GOTO ENDIT
%%ENDIF
%%IF %%OMONTH EQ 11
%%SET %%MON = NOV
%%GOTO ENDIT
%%ENDIF
%%IF %%OMONTH EQ 12
%%SET %%MON = DEC
%%GOTO ENDIT
%%ENDIF
%%LABEL ENDIT
The above lines are usually commented out in the JCL and they are meant to be valid only on the Control-M system. In the JCL, we assign the following Control-M variable names (%%MON & %%OYEAR) to MMMYY symbolic override.
MMMYY=%%MON.%%OYEAR
During runtime of the JCL, the values are substituted. These jobs are scheduled in Control-M to run in a particular time of the month and they don't need manual intervention. Hope this helps.
As cschneid said, I strongly suggest you to get in touch with the schedulers in your site.