#!perl
use strict;
use warnings;

my $memory_eaten = 8 * 1024 * 1024 * 1024; # 8GB, adjust to fit

my %memory_eater = (
    foo => scalar( " " x $memory_eaten ),
);

my $cmd = "foo bar";
system($cmd) == 0
    or die "Couldn't launch '$cmd': $!/$?";