What decides the order of keys when I print a Perl

Question

activePerl 5.8 based

#!C:\Perl\bin\perl.exe
use strict;
use warnings;

# declare a new hash
my %some_hash;

%some_hash = ("foo", 35, "bar", 12.4, 2.5, "hello",
      "wilma", 1.72e30, "betty", "bye\n");

my @any_array;
@any_array = %some_hash;

print %some_hash;
print "\n";
print @any_array;
print "\n";
print $any_array[0];
print "\n";
print $any_array[1];
print "\n";
print $any_array[2];
print "\n";
print $any_array[3];
print "\n";
print $any_array[4];
print "\n";
print $any_array[5];
print "\n";
print $any_array[6];
print "\n";
print $any_array[7];
print "\n";
print $any_array[8];
print "\n";
print $any_array[9];

Output as this

D:\learning\perl>test.pl
bettybye
bar12.4wilma1.72e+030foo352.5hello
bettybye
bar12.4wilma1.72e+030foo352.5hello
betty
bye

bar
12.4
wilma
1.72e+030
foo
35
2.5
hello
D:\learning\perl>

What decided the elements print order in my sample code?

Any rule to follow when print a mixed(strings, numbers) hash in Perl? Thank you.

bar12.4wilma1.72e+030foo352.5hello

[Updated]

With you guys help, i updated the code as below.

#!C:\Perl\bin\perl.exe
use strict;
use warnings;

# declare a new hash
my %some_hash;

%some_hash = ("foo", 35, "bar", 12.4, 2.5, "hello",
      "wilma", 1.72e30, "betty", "bye");

my @any_array;
@any_array = %some_hash;

print %some_hash;
print "\n";
print "\n";
print @any_array;
print "\n";
print "\n";

my @keys;
@keys = keys %some_hash;
for my $k (sort @keys)
{
    print $k, $some_hash{$k};
}

output

D:\learning\perl>test.pl
bettybyebar12.4wilma1.72e+030foo352.5hello

bettybyebar12.4wilma1.72e+030foo352.5hello

2.5hellobar12.4bettybyefoo35wilma1.72e+030
D:\learning\perl>

Finially, after called keys and sort functions. The hash keys print followed the rule below

2.5hellobar12.4bettybyefoo35wilma1.72e+030

Answer 1

From perldoc -f keys:

The keys of a hash are returned in an apparently random order. The actual random order is subject to change in future versions of Perl, but it is guaranteed to be the same order as either the values or each function produces (given that the hash has not been modified). Since Perl 5.8.1 the ordering is different even between different runs of Perl for security reasons (see Algorithmic Complexity Attacks in perlsec).

...

Perl has never guaranteed any ordering of the hash keys, and the ordering has already changed several times during the lifetime of Perl 5. Also, the ordering of hash keys has always been, and continues to be, affected by the insertion order.

Also note that while the order of the hash elements might be randomised, this "pseudoordering" should not be used for applications like shuffling a list randomly (use List::Util::shuffle() for that, see List::Util, a standard core module since Perl 5.8.0; or the CPAN module Algorithm::Numerical::Shuffle), or for generating permutations (use e.g. the CPAN modules Algorithm::Permute or Algorithm::FastPermute), or for any cryptographic applications.

---

Note: since you are evaluating a hash in list context, you are at least guaranteed that each key is followed by its corresponding value; e.g. you will never see an output of a 4 b 3 c 2 d 1.

Answer 2

Hashes are not (necessarily) retrieved in a sorted manner. If you want them sorted, you have to do it yourself:

use strict;
use warnings;

my %hash = ("a" => 1, "b" => 2, "c" => 3, "d" => 4);

for my $i (sort keys %hash) {
    print "$i -> $hash{$i}\n";
}

You retrieve all the keys from a hash by using keys and you then sort them using sort. Yeah, I know, that crazy Larry Wall guy, who would've ever thought of calling them that? :-)

This outputs:

a -> 1
b -> 2
c -> 3
d -> 4