10.2. \ - Taking a Reference to an Existing Variable
In Perl the backslash (\) is an operator that returns the reference to an existing variable. It can also return a dynamic reference to a constant.
Here is an example that uses a reference to update a sum:
use strict; use warnings; my $sum = 0; sub update_sum { my $ref_to_sum = shift; foreach my $item (@_) { # The ${ ... } dereferences the variable ${$ref_to_sum} += $item; } } update_sum(\$sum, 5, 4, 9, 10, 11); update_sum(\$sum, 100, 80, 7, 24); print "\$sum is now ", $sum, "\n";
As can be seen, because the reference to $sum was used, its value changes throughout the program.