(echo ">chr1"; \
echo "ACGT") > ref.fa
(echo "##fileformat=VCFv4.2"; \
echo "##contig=<ID=chr1,length=248956422>"; \
echo "##INFO=<ID=END,Number=1,Type=Integer,Description=\"Stop position of the interval\">"; \
echo -e "#CHROM\tPOS\tID\tREF\tALT\tQUAL\tFILTER\tINFO"; \
echo -e "chr1\t1\t.\tA\t<NON_REF>\t.\t.\tEND=2") | \
bcftools view -Oz -o a.vcf.gz && bcftools index -ft a.vcf.gz
(echo "##fileformat=VCFv4.2"; \
echo "##contig=<ID=chr1,length=248956422>"; \
echo -e "#CHROM\tPOS\tID\tREF\tALT\tQUAL\tFILTER\tINFO"; \
echo -e "chr1\t1\t.\tA\tC\t.\t.\t.") | \
bcftools view -Oz -o b.vcf.gz && bcftools index -ft b.vcf.gz
bcftools merge -g ref.fa a.vcf.gz b.vcf.gz -m none -o /dev/null