The answers above are more informative than this one will be. But your post inspired me to play with IPC::Shareable. It allows you to put variables into shared memory and access them from separate scripts. This is just a toy example and I don't have the experience required to recommend this as a solution. But it may be instructive.

It consists of two scripts, adult.pl which will run child.pl in the background. After they're both running they each update a shared array.

adult.pl:

use IPC::Shareable;
use Data::Dump qw(ddx);
$| = 1;

# Setup shared array reference "my_var"
my $id = 'my_special_name';
my %options = (create => 'yes', exclusive => 0, mode => 0644, destroy 
+=> 'yes');
my $my_var;
tie $my_var, 'IPC::Shareable', $id, { %options } or die "tie failed: $
+!\n";
$my_var = [0..10];

system('./child.pl &');

until ($my_var->[-1] == 999) {
    my $num = int(rand()*100);
    push @$my_var, $num;
    ddx [ @$my_var ];
    sleep 2;
};

print "Leaving adult.pl..\n";
[download]

child.pl:

use IPC::Shareable;
use Data::Dump qw(ddx);
$| = 1;

my $id = 'my_special_name';
my %options = (create => 0, exclusive => 0, mode => 0644, destroy => 0
+);
my $my_var;
tie $my_var, 'IPC::Shareable', $id, { %options } or die "tie failed: $
+!\n";

for (0..3) {
    my $num = int(rand()*100);
    push @$my_var, $num;
    ddx [ @$my_var ];
    sleep 2;
}

push @$my_var, 999;
print "Leaving child.pl..\n";
[download]

Output:

# adult.pl:20: [0 .. 10, 16]
# child.pl:16: [0 .. 10, 16, 72]
# adult.pl:20: [0 .. 10, 16, 72, 52]
# child.pl:16: [0 .. 10, 16, 72, 52, 17]
# adult.pl:20: [0 .. 10, 16, 72, 52, 17, 66]
# child.pl:16: [0 .. 10, 16, 72, 52, 17, 66, 96]
# adult.pl:20: [0 .. 10, 16, 72, 52, 17, 66, 96, 92]
# child.pl:16: [0 .. 10, 16, 72, 52, 17, 66, 96, 92, 88]
# adult.pl:20: [0 .. 10, 16, 72, 52, 17, 66, 96, 92, 88, 56]
Leaving child.pl..
Leaving adult.pl..
[download]

* Note that they share data based on a named id, which means their connection can be established without the child script being started by the adult.