To make variables persistent between subroutines, you can simply declare them outside the subroutines:

#!/usr/local/bin/perl -w

use strict;

BEGIN {
my $static = 0;

sub inc {
  ++$static;
}

sub dec {
  --$static;
}

}

$, = $\ = "\n";
print inc(), inc(), dec(), dec();
[download]

The block creates a private scope, so that $static is available only to the inc() and dec() functions. Adding BEGIN before the block ensures that $static is initialized before the subroutines are called.