How to split a dat file based on another file ni UNIX?

i have two files , one is var.txt and another res.dat file

var.txt contains informaton like below

date,request,sales,item

20171015,1,123456,216

20171015,1,123456,217

20171015,2,345678,214

20171015,3,456789,218

and res.dat contains is a one huge file contains information like below

RTCCVB01 213456 123456 216

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VBPCVB01

RTCCVB01 213456 345678 214

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VBPCVB01

RTCCVB01 213456 123456 217

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VBPCVB01

RTCCVB01 213456 456789 218

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.

VBPCVB01

For a unique request i have to create a separate dat file, for example

for Request 1

123456.dat

RTCCVB01 213456 123456 216

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.

VBPCVB01

RTCCVB01 213456 123456 217

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.

VBPCVB01

for Request 2 345678.dat

RTCCVB01 213456 345678 214

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.

VBPCVB01

for Request 3 456789.dat

RTCCVB01 213456 456789 218

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VBPCVB01

sales occur at 50-56 position in res.dat file item occur at 72-79 position in res.dat file

i have to write a shell script which will do below for each unique request from var.txt it will take sales and item and extract information from res.dat and will be creating separate dat files till all request number is done .

Ignoring that there's neither positions 50-56, nor 72-79, and the Request-No doesn't occur anywhere in your output, i.e. the first file is never used, try

awk '
/^RTCC/         {FN = $3 ".dat"
                }
                {print > FN
                }
'  res.dat