I’m not exactly clear on what you want, but the CPAN module Capture::Tiny will almost certainly meet your needs. For example (from the documentation):

($stdout, $stderr, $exit) = capture { system($cmd, @args); };
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Update: For your specific example:

#!usr/bin/perl

use strict;
use warnings;
use Capture::Tiny qw(capture);

my ($stdout, $stderr, $exit) = capture
{
    system('ls', '-l');
};

print "After the system call:\n";
print "\$stdout = $stdout\n";
print "\$stderr = $stderr\n";
print "\$exit   = $exit\n";
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Hope that helps,