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why JCL has //

 
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vidhyanarayanan

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Joined: 23 Dec 2005
Posts: 52

PostPosted: Wed Apr 19, 2006 3:21 pm    Post subject: why JCL has //
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Hi all,

why JCL has slashes // in col1 and col2 of each STATEMENT?
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dneufarth

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Joined: 27 Apr 2005
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Location: Cincinnati OH USA

PostPosted: Wed Apr 19, 2006 7:22 pm    Post subject:
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identifies it as JCL as opposed to inline data or JES control statements
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pspreddy

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PostPosted: Thu Apr 20, 2006 1:22 am    Post subject:
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The identifier field is the first field in a JCL statement.

Two slashes, //, in positions 1 and 2 instruct the computer to expect a JCL statement.

A slash and an asterisk (/*) in positions 1 and 2 identify a JES2 statement.

If you are entering data, omit the identifier.

Thanks
Shiva
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Bharanidharan

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Joined: 20 Jun 2005
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PostPosted: Thu Apr 20, 2006 3:43 pm    Post subject: Re: why JCL has //
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The root goes far back in time!
The pioneers, when designing a language for MVS to interpret which they knew would be used forever, arrived at a consensus that all JCL commands/statements to be appended with // in the punched cards such that card reader would know that the cards necessarilly contain commands to get the job done in mainframe.
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superk

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Joined: 26 Apr 2004
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PostPosted: Fri Apr 21, 2006 9:09 pm    Post subject: Re: why JCL has //
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Back when punched cards were used to submit JCL, if the cards were mistakenly loaded into the reader incorrectly, the slashes wouldn't be read first and the card deck would be rejected.
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