Hash Keys (strings or numbers?)

[robot_tourist]

Just as there are different operators for comparing strings and numbers, you should be aware how that affects accessing elements of hashes.

Consider the following:

my $key1 = '00001';
my $key2 = 1;
my %hash1 = (1 => 1);
my %hash2 = (1 ,  2);
my %hash3;
   $hash3{$key1} = 3;
my %hash4;
   $hash4{$key2} = 4;

Obviously, $key1 == $key2, but $key1 ne $key2. That is, they are equal as numbers, but since $key1 is a string and $key2 is not, then they will not match using the eq string operator. This leads to the following:

00001 == 1       That is: $key1 == $key2
00001 ne 1       That is: $key1 ne $key2

$hash1{$key1} is undef
$hash1{$key2} == 1
$hash2{$key1} is undef
$hash2{$key2} == 2
$hash3{$key1} == 3
$hash3{$key2} is undef
$hash4{$key1} is undef
$hash4{$key2} == 4

This is particularly important when working with databases, for example, where the key field may be zerofilled.