I'm not sure I understand the question, and as btrott already said you probably might have wanted to use eq instead. Anyway...

# this works
my $date = 'dec';
foreach ('november', 'december') {
    print "yeah, we ski in $_\n" if /$date/;
}

# this doesn't
my $date = 'december';
foreach ('nov', 'dec') {
    print "yeah, we ski in $_\n" if /$date/;
}
[download]

#!/home/bbq/bin/perl
# Trust no1!