Is there a way to extract one SNP by POS from a large vcf file.
you asked many questions on this site. it would be nice if you could validate the correct answers (green ticks on the left).
tabix, see the example in the manual: http://www.htslib.org/doc/tabix.html
Essentially you compress the file with bgzip, then index with tabix and then use tabix your.vcf.gz chr:start-end for retrieval.
tabix your.vcf.gz chr:start-end