$haha = 'I have black tyres.';
$haha=`echo $haha | sed "s/tyre/tire/g"`;
print($haha, "\n");
# outputs: I have black tires.

##</code><code>##

$haha = 'I have black tyres.';
$haha =~ s/tyre/tire/g;
print($haha, "\n");
# outputs: I have black tires.