search tools：blastn, blastp, blastx, tblastx, tblastn, psiblast, rpsblast, and rpstblastn
1.blastn: 核酸序列vs核酸库
$blastn -query file-in -db database -out file_out -evalue 0.00001 -max_target_seqs 5 -num_threads 4 -outfmt format "7 qacc sacc evalue length pident"
-evalue :设置E值阀值
-max_targe_seqs :Maximum number of aligned sequences to keep. -max_target_seqs <Integer, >=1>
-num_threads 4: 线程数
-output：输出格式，7代表一种格式，后面是内容。7 = tabular with comment lines
2.blastp: