#!/usr/bin/perl

use strict;
use warnings;
use Readonly;

Readonly my $size => 10 * 1024 ** 2; # 10 Mb.

sub show_mem {
    system "grep ^VmSize /proc/$$/status";
}

sub gimme_big {
    my $size = shift;
    my $var  = eval "'x' x $size";
    undef $var;
}

show_mem;
gimme_big $size;
show_mem;

__END__
VmSize:     3468 kB
VmSize:     3468 kB