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DCB when using DUMMY parameter necessary?

 
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senjay

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Joined: 10 May 2007
Posts: 147
Location: India

PostPosted: Tue Jul 24, 2007 6:07 pm    Post subject: DCB when using DUMMY parameter necessary?
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hi,

when we are using DUMMY parameter, do we need to mention LRECL and RECFM? if yes, when?
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mainframe_96

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Joined: 18 Dec 2006
Posts: 13
Location: usa

PostPosted: Tue Jul 24, 2007 6:47 pm    Post subject:
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DCB Parameter for DD dummy is unnecessary.
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Anuj Dhawan

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Joined: 22 Apr 2006
Posts: 6258
Location: Mumbai, India

PostPosted: Tue Jul 24, 2007 7:08 pm    Post subject:
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Hi,

The DUMMY parameter specifies that no device is to be allocated to this DD statement and that no disposition processing or I/O is to be done. All other JCL parameters on a DUMMY DD statement have to be syntactically correct. Use the DUMMY parameter if you know you will not need a file in a job step.

Code AMP=AMORG if you are using DUMMY with a VSAM file.

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


P.S.: There have been discussions on DUMMY parameter, please make a search or look in the manuals for better understanding.
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mmwife

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Joined: 30 May 2003
Posts: 1592

PostPosted: Wed Jul 25, 2007 5:12 am    Post subject:
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Hi Senjay,

The LRECL may be necessary. It depends on the pgm that uses the file. Some IBM Utils require it. I don't recall which ones.

But you can test w/o the LRECL. If the pgm fails w/a msg pointing to the DUMMY file, you'll know.
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Anuj Dhawan

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Joined: 22 Apr 2006
Posts: 6258
Location: Mumbai, India

PostPosted: Thu Jul 26, 2007 3:26 pm    Post subject:
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Hi,

Because no I/O is performed to the dummy data set, the system checks the SPACE and DISP parameters, if coded, for syntax, then ignores them. If you code UNIT with DUMMY, the system will ignore it if the specified unit name is syntactically correct and defined to the system. Otherwise the system terminates the job. Thus line from mmwife follows:
Quote:
But you can test w/o the LRECL. If the pgm fails w/a msg pointing to the DUMMY file, you'll know.

Hope this helps.
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