Peruse perlipc and take a look to see what applies best to you. Pipes, sockets, signals, or perhaps just print to STDOUT and capture it with backticks.

Also common would be to centralize and use modules instead of cascading scripts.

If you are set on multiple scripts, you can use globals (our) combined with do (or require) rather than system. But this is probably not a good idea for new code, since this gets messy fast, and the execution environments can have odd effects on each other.

#!/usr/bin/perl -w
use strict;

our $x = 1;
require 'script2.pl';
print $x;
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#!/usr/bin/perl -w
use strict;

our $x = 2;
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SuicideJunkie's suggestions are where you should look first (maybe even w/ a fork and exec); however, if you are dealing with legacy, this might help.