Uninitialized value message

[carg1]

In a script I'm working on, I'm using this block of code to convert a file's Date Modified as the filename for the output file:

#Ops stores the stat function ran on the previous input.
$Ops = (stat($DB))[9];

#Converts the date to a readable format
($sec, $min, $hour, $mday, $mon, $year, $wday, $yday, $isdst) = localtime($Ops);
$RMonth = $mon + 1; #Adds one to month to obtain the correct month
$SYear = ($year % 100); #Runs modulo arithmetic on the year to get the correct short year
@DateMod = ($RMonth, $mday, $SYear, $hour, $min);

#Stores the value of Ops, converted into a readable format, into the variable $Stuff
$Filename = sprintf("%02d%02d%02d%02d%02d", @DateMod);

It tells me I have an uninitialized value in

($sec, $min, $hour, $mday, $mon, $year, $wday, $yday, $isdst) = localtime($Ops);

when I run it with the -w option. I'm not exactly sure why it's telling me that. It's a part of a script that I'm integrating into one bigger script. More clearly, the script that contains that block of code used to be a standalone script. Now I'm integrating it into a script that runs that script and a few others through a menu. I have no problem getting any of the scripts to run, but that date issue is a major one since it names the output file based on that returned date. All the names it creates contain "1231691900" as the date.

In the menu, I want it to output the name of the open file:

INPUT2: print "\n\n\nWhat would you like to do next?\n\n";
print "The currently open file is: $Dir"."$DB\n\n";
print "1) Open another file\n";
print "2) Filter hits by blocked content\n";
print "3) Filter hits by passed content\n";
print "4) Count IP address instances\n";
print "5) Filter hits by IP address\n";
print "6) Exit the program\n";
print "\n\nYour choice: ";
$PickNumber = <STDIN>;
chomp($PickNumber);

It says the variables in the concatenation are uninitialized. I use the variables $Dir and $DB in an if statement that follows that, could that be why? I tried using defined in both cases, maybe I used it wrong, but that didn't work. I admittedly don't completely understand the concept of "defined", I just saw that someone used that as a solution when I did a keyword search on the forum. Is there something I'm missing?