In the [VCF format][1], there is the option for the ID field to have multiple semi-colon separated values. In theory, there could be two dbSNP rsIDs in a single line (i.e. two indels at chr:pos), but for programming purposes, that should not happen, correct? dbSNP has merged all variants for a given position to a common rsID? 


  [1]: https://samtools.github.io/hts-specs/VCFv4.3.pdf
> dbSNP has merged all variants for a given position to a common rsID? 

I'm afraid no:

    $ wget -q -O - "ftp://ftp.ncbi.nih.gov/snp/organisms/human_9606/VCF/All_20180418.vcf.gz" | gunzip  -c | grep -v "#" | cut -f 1,2 | uniq -d  | head
    1	10051
    1	10055
    1	10108
    1	10109
    1	10128
    1	10132
    1	10177
    1	10228
    1	10229
    1	10235
.

    $ wget -q -O - "ftp://ftp.ncbi.nih.gov/snp/organisms/human_9606/VCF/All_20180418.vcf.gz" | gunzip  -c | grep -v "#" | cut -f 1,2,3,4,5 | grep -w 10051 -m2
    1	10051	rs1052373574	A	G
    1	10051	rs1326880612	A	AC

