code: def run_vecscreen(infile=None, outfile=None, db="UniVec_Core",
          pctid=None, hitlen=None):
      
      db = get_abs_path(db)
      nin = db + ".nin"
      run_formatdb(infile=db, outfile=nin)
  
      cmd = "blastn"
      cmd += " -task blastn"
      cmd += " -query {0} -db {1} -out {2}".format(infile, db, outfile)
      cmd += " -penalty -5 -gapopen 4 -gapextend 4 -dust yes -soft_masking true"
      cmd += " -searchsp 1750000000000 -evalue 0.01 -outfmt 6 -num_threads 8"
      sh(cmd)
docs: BLASTN parameters reference:
      http://www.ncbi.nlm.nih.gov/VecScreen/VecScreen_docs.html