perl -e '(@x)=$ARGV[0]=~/\[(.*?)\]/g; print qq|$x[$#x];\n|' "enoyl-[acyl-carrier-protein] reductase [NADH] 2 [Silicibacter sp. TrichCH4B]. "
#--output---
Silicibacter sp. TrichCH4B;

##</code><code>##

    /\[([^\]]+)\]/