Hash in Scalar Context - Perl

A hash in scalar context is shown in this example:

#!/usr/bin/perl -w
# scalarcontext.pl

use strict;

my %person = (
    name  => 'John Doe',
    age   => 39,
    phone => '555-1212',
    city  => 'Chicago'
);

my $scalar = %person;

print "scalar context: $scalar\n";

if (%person) {
    print "%person has at least one key/value pair\n";
} else {
    print "%person is empty!\n";
}

Executing this program produces the following:

$ perl scalarcontext.pl
scalar context: 3/8
%person has at least one key/value pair
$

This code produces an unexpected result. The following code:

my $scalar = %person;

print "scalar context: $scalar\n";

prints the string “scalar context: 3/8”. Therefore, this hash in scalar context is “3/8” which means that we are using three buckets, or memory locations, out of eight buckets allocated.

This string is not so interesting unless we notice that the string “3/8” is a true value in Perl. Also, if our hash was empty, its value in scalar context would be the empty string, "". So a hash in scalar context is normally treated as a true/false value—true if there is anything in it, false if empty:

if (%person) {
    print "%person has at least one key/value pair\n";
} else {
    print "%person is empty!\n";
}