annotate_variation.pl 根据snpid 获取基因信息，给个例子，解释一下参数的用法

An example of using annotate_variation.pl to retrieve gene information based on SNP ID is as follows:

./annotate_variation.pl -buildver hg19 -downdb -webfrom annovar avsnp147 humandb/
./annotate_variation.pl -buildver hg19 -out output -webfrom annovar -protocol refGene,avsnp147 -operation g,f -nastring . inputfile.txt humandb/

In this example, we first download the avsnp147 database for human genome version hg19 using the "-downdb" and "-webfrom annovar" options. This database contains information about SNPs and their annotations.

Next, we use annotate_variation.pl to annotate a set of SNPs in the inputfile.txt file using the refGene and avsnp147 protocols. The "-protocol" option specifies which protocols to use, and the "-operation" option specifies which type of annotation to perform. In this case, we are annotating the SNPs with gene information (g) and functional predictions (f).

Finally, we specify the output file name using the "-out" option, and the path to the database files using the "humandb/" argument.

In summary, the main parameters used in annotate_variation.pl are:

- "-buildver": specifies the genome build version
- "-downdb": downloads the specified database
- "-webfrom annovar": specifies the source of the database
- "-protocol": specifies which annotation protocols to use
- "-operation": specifies which type of annotation to perform
- "-nastring": specifies the output value for missing data
- input file: the file containing the SNP IDs to annotate
- database directory: the path to the database files