#The result of the equality check is used in "boolean context"
if ($foo ne $bar) {
  print "Mismatch!";
};

#The result of the equality operator is used in "other context":
my $diff_start = ($foo ne $bar);

#The result of the equality operator is also used in "other context":
if (my $diff_start = ($foo ne $bar)) {
  print "Mismatch after $diff_start";
};