A closure is a code block with lexcially scoped variables. But only use them if you've got a good reason for that.

This is a simple example of what a closure is and how it works:

sub closure {
    my $a = $_[0];
    return sub { $a += 2 };
}

my $first = closure(1);

print $first->(), "\n"; # 3
print $first->(), "\n"; # 5

my $second = closure(14);

print $second->(), "\n"; # 16
print $first->(), "\n"; # 7
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Only with dynamic information (like the $a's in this example), closures are useful.

2;0 juerd@ouranos:~$ perl -e'undef christmas'
Segmentation fault
2;139 juerd@ouranos:~$
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