The other posts provide good insight, but if you really want to know what a data structure looks like one of the simplest methods is to do this:

use Data::Dumper;

# .......

print Dumper( $abc );
[download]

You'll get a dump of the data structure on your screen. Very useful for getting a snapshot of what you're working with. Sometimes I'm even the one who created the structure, and I will use Data::Dumper to verify that it looks as I expected it to.