my $num = $_ = 4;
if($num >= 0) {
   die "$num is positive";
} else {
   die "$num is negative (but we already knew that)";
}

# or even ;)
my $num = $_ = -4;
if(substr($num,0,1,) eq '-') {
   die "I, $num, feel so negative today";
} else {
   die "$num says 'Things are looking up'";
}