use vars qw( $x );      # a package global

$x = 'outer';

# this block:
{
  my $save_x = $x;      # localize $x by saving its  value
  $x = 'inner';         # change $x to hearts content

  some_sub( $x );       # some_sub() sees $x with value 'inner'

  $x = $save_x;         # restore original value just before exiting block
}

# is functionally identical to this block:
{
  local $x = 'inner';

  some_sub( $x );
}

# in both cases, some_sub() is called with the package global $x set
# to 'inner' and in both cases, the value of $x is restored when the
# block exits, except in the 'local' case, it is not necessary to
# explicitly restore $x