I instantiate the module without naming the file, then call get_lines with the file name. It doesn't need to be passed as an argument to get_filehandle because it's already there.

Yes, you're right, because you call get_filehandle inside of get_lines, it actually could make sense to pass the filename to the get_lines call. However, I think it could potentially still be confusing because with the code you showed, if all the user uses is get_lines, it'll only ever open one file - say I call my $x = $obj->get_lines("foo.txt"), and then my $y = $obj->get_lines("bar.txt"), now $y contains the second line of foo.txt. So that's why it might be better to separate the two actions - opening the file and reading from it - into two methods.

Update: The reason I questioned whether it makes sense to pass a filename to get_filehandle is that I was imagining $self->{file} to be an object property that might deserve its own setter, but that's not as important. BTW, you might want to consider renaming get_filehandle to something like open_file to make it more clear what the method is doing.