my $pid;
my $enough = 120;

if ( $pid = fork ) {
    # parent
    sleep $enough;
    unless ( system( "ps -p $pid >/dev/null" ) ) { # 0 exit code means
+ found
        warn "feeling filicidal (plus item description)\n";
        system "kill -9 $pid >/dev/null 2>&1";
    }
}
else { # child
    ... install item ...
    exit;
}
[download]

Updated