Your use of $4 in this line is incorrect:
Code:
awk "BEGIN {i=$1;j=$2;k=$3 ; for (x=i;x<=j;x=x+k) {print $4 x}}";;
In that context it tells awk to print the 4th field, which doesn't exist.
You could pass your value to awk as a parameter:
Code:
awk "BEGIN {i=$1;j=$2;k=$3 ; for (x=i;x<=j;x=x+k) {print ARGV[1] x}}" $4;;
Which will give you:
#./nu 1320 1339 1 CMUR0
4 1320 1339 1 CMUR0
CMUR01320
CMUR01321
CMUR01322
CMUR01323
CMUR01324
CMUR01325
CMUR01326
CMUR01327
CMUR01328
CMUR01329
CMUR01330
CMUR01331
CMUR01332
CMUR01333
CMUR01334
CMUR01335
CMUR01336
CMUR01337
CMUR01338
CMUR01339