Using a hash to look up for the months, the values for the keys are the order of the months in the calendar while the keys are each month's name ...

#!/usr/local/bin/perl
use strict;
use warnings;

my %monthsOrder;
@monthsOrder{qw(Jan Feb Mar Apr May Jun Jul Aug Sept oct Nov Dec)}=1..
+12;
#provide a list of dates to convert
my @dates = ('Nov-07', 'Aug-09', 'Jul-01', 'Feb-02');

foreach my $element (@dates){
        my ($month, $year)= $element=~/(\w+)-(\d+)/;
        print convertMonth($month, $year),"\n";
        }

sub convertMonth{
    my ($month, $year) = @_;
    for my $key(keys %monthsOrder){
        return "20$year/$monthsOrder{$key} " if $month eq $key;
        }
    }
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Output:

2007/11
2009/8
2001/7
2002/2
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Updated to account for passing an array of different dates..