2.4.5 Assignment with Operators
It should be duly noted that it is possible to concatenate, like in C, an
operator onto the assignment statement to abbreviate using the left hand
side as the first operand. For example,
use strict;
my $greet = "Hi! ";
$greet .= "Everyone\n";
$greet = $greet . "Everyone\n"; # Does the same operation
# as the line above
This works for any simple, binary operator.