Another way to find out what is in mystery structures is to use the debugger. run the program with -d ie perl -d foo.pl put in a breakpoint at the lines in question ie b 15 (where line 14 was your $srciphash{$srcip}{$dstip} = 1; c (continue till the breakpoint) print @srciphash - will show you that it contains a pointer not normal data. x @srciphash shows the structure and what the structure contains. Hope this helps.