Don't need to be in perl. If you're working with tab separated values (so outfmt 6) , you can easly do a filter with awk. Assuming evalue is on the 4th column, thìs command will print only lines where evalue is lower than 0.02

awk -F'\t' '$4 < 0.02 {print ;}'

Same things could be done with every params. Remember always to declare which is the field separator, said after "-F" arguments. Field starts to be counted from $1, because $0 is the whole line.

To get just the first results, assuming your blast query reports output from most representative record to the less representative one, you can do again a trick with awk. $1 is used assuming your query id is on the 1st field.

awk '!seen[$1]++'