unless (my $speciesname eq (my specieslist{$entry})) { You don't blindly put my in front of every variable. It is a way to declare variables, so you only put it in front of the first use of a variable (and in a scope where every other use can 'see' it). First, 'specieslist' is a hash, so somewhere you would have 'my %specieslist;' or 'my %specieslist = ....;'. and so speciesname and specieslist in your clause above would not have a my.

And your clause above also has another typo, the lack of a '$' in front of specieslist (but I'm just assuming that's just a typo here from your error message). FYI, you are declaring a new lexical variable '$speciesname' above, which is only scoped (it only exists) in the 'unless' block, and it has an undefined value.

Update: Just noticed this node that might help.