awk -F'[,:]' '                                       # separate by a coma or a colon
BEGIN{
    print "COUNT,BNG_IP,PORT,OVLAN,DSLAM_IP"         # start by displaying the header
}
{
    gsub(" ", "")                                    # remove any spaces to sanitize the input
}
FNR==NR {                                            # apply the following block rule to the first file
    I[$2,$3,$4]=$0                                   # make the fields 2,3,4 as an id for the array I and save the whole line in it
    next                                             # stop processing any more blocks and go to read the next record
}
I[$1,$3,$4]{                                         # if it gets here, it is processing the second file. Check there's something in for the key of fields
    print I[$1,$3,$4], $2                            # if an ID matches, display the whole record from file 1 + the added DSLAM_IP from file 2
}' OFS=',' surender_reddy.file1 surender_reddy.file2 # OFS (Output Field Separator) is set to be a coma

COUNT,BNG_IP,PORT,OVLAN,DSLAM_IP
22,10.238.60.129,1/1,2009,10.232.0.9
8,10.238.60.129,2/1,2310,10.232.2.10
9,10.238.60.129,2/1,2312,10.232.2.12
4,10.238.60.129,2/1,2313,10.232.2.13
1,10.238.60.129,2/1,2316,10.232.2.16

awk -F, '                                             # use a coma as input separator
        {gsub (/ /,_)}				      # substitute any white space for an underscore to balance the input										
NR==FNR {split ($NF, T, ":")                          # for the first file, split the last field by colon and save it into an array T
         DSLAM[$1,$3,T[1]]=$2                         # create an array named DSLAM with the id made up from $1,$3,T[1] to save $2
         next                                         # move to the next record and skip the rest if this is file2
        }
FNR==1  {print $0 FS "DSLAM_IP"                       # only for the first line of the second file,since the first file has been processed already. Print header.
         next			                      # skip the rest if it is the record is the first line of the second file at stdin
        }
($2,$3,$4) in DSLAM     {print $0 FS DSLAM[$2,$3,$4]} # if there a key named $2,$3,$5 in the previous made array DSLAM, display current line + coma + content stored in DSLAM[key].
' file2 file1