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Need information DUMMY in the JCL

 
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sureshbabu.jv

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Joined: 11 Apr 2006
Posts: 41
Location: Chennai

PostPosted: Tue Sep 05, 2006 8:18 pm    Post subject: Need information DUMMY in the JCL
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The code is written the JCL like below

//STEP1 DD DUMMY DISP=(new,delete,delete),UNIT=SYSDA

what's the mean of above statement.Can you please give me idea on this.

Thanks,
Sureh
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superk

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Joined: 26 Apr 2004
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Location: Raleigh, NC, USA

PostPosted: Tue Sep 05, 2006 9:42 pm    Post subject: Re: Need information DUMMY in the JCL
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This is an equivalent statement:

//STEP1 DD DSN=NULLFILE, DISP=(NEW,DELETE,DELETE),UNIT=SYSDA

does this make more sense?
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lucky.rohith
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PostPosted: Wed Sep 06, 2006 7:41 am    Post subject: Re: Need information DUMMY in the JCL
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that statement is used to create a temporary data set.
Once if v spicefiy tat DUMMY in the JCl,it means tat our program is not taking any input stream.
//STEP1 DD *
INPUT DATA
/*
Through this statements the input can b passed to our program.
These must b coded in RUNJCL.
//STEP DD DUMMY
This statement in the RUNJCL specifies tat our program not taking any input stream.

DISP=(NEW,DELETE,DELETE)
This parameter says that the NEW dataset should b created temporary when ever program is executed.After running the progam this dataset must b DELETED from the cataloglist.


Upto My KNOWLEDGE i've given u the info.If any wrong in my explanation u can reply me.
I wil b pleaed if u do so.

Reguards
Uday
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mmwife

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Joined: 30 May 2003
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PostPosted: Wed Sep 06, 2006 7:52 am    Post subject:
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Hi Sureh,

If the JCL was codes EXACTLY as you show, //STEP1 defines a DUMMY dataset and the "DISP=(new,delete,delete),UNIT=SYSDA" are comments.

Whoever wrote that may have started with:

//STEP1 DD DSN=ds1,DISP=(new,delete,delete),UNIT=SYSDA

and overtyped the DSN field, keeping the rest so he wouldn't have to retype it when he put the DSN back.
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rajeshbook

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Joined: 21 Nov 2005
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PostPosted: Wed Sep 06, 2006 3:26 pm    Post subject:
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DD statement STEP1 defines a dummy data set. The other parameters coded on the statement are checked for syntax but not used. So all parameters coded on a DD DUMMY statement must be syntactically correct. The system checks their syntax.There are two common use of coding DUMMY parameter like this,

One use of the DUMMY parameter is in testing a program. When testing is finished and you want input or output operations performed on the data set, replace the DD DUMMY statement with a DD statement that fully defines the data set.

Another use of the DUMMY parameter is in a cataloged or in-stream procedure. Code on the DD DUMMY statement all the required parameters. When the procedure is called, nullify the effects of the DUMMY parameter by coding on the DD statement that overrides the DD DUMMY statement a DSNAME parameter that matches the DSNAME parameter on the DD DUMMY statement. For example,
procedure step PS contains the following:

//DS1 DD DUMMY,DSNAME=A,DISP=OLD

Nullify the DUMMY parameter by coding:
//JS EXEC PROC=PROC1
//PS.DS1 DD DSNAME=A

Hope it makes clear...

Rajasekar
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