Global variable vs. function with argumet

var-vs-arg.pl

#
# 1. global variable
#
my $num = 2;
exp();

sub exp {
  return $num * $num;
}

#
# 2. function with argument
#
my $num = 2;
exp($num);

sub exp {
  my $num = shift;  # local to exp

  return $num * $num;
}