How do I extract the value from a nested hash with unknown level of nesting? - perl

Question

What is the best way to walk a nested hash structure to get the value when there can be an unknown number of nested levels?
For example the hash could be any of the following or any level of nesting.
my $hash = { 'known' => { 'a' => { 'b' => 'value' } } };
my $hash = { 'known' => { 'a' => { 'b' => { 'c' => 'value' } } } };
my $hash = { 'known' => { 'a' => { 'b' => { 'c' => { 'd' => 'value' } } } } };
The keys a,b,c below could be any value.
I was thinking I could do it with a recursive function that extracts the key and value and the current level, checks to see if the value is a reference to
a hash and if so calls itself, otherwise I have the value?

Answer 1

An easy-to-read approach:
#!/usr/bin/env perl
use strict;
use warnings;
my $hash = { 'known' => { 'a' => { 'b' => 'value' } } };
print get_deep_values($hash);
sub get_deep_values {
my $hash = shift;
if (ref($hash) eq 'HASH') {
get_deep_values( (values %$hash)[0] )
}
else {
return $hash;
}
}
Output:
value

Answer 2

Yes, recursion works,
use v5.16;
use warnings;
my $hash = { 'known' => { 'a' => { 'b' => 'value' } } };
print sub { map { ref() ? __SUB__->(values %$_) : $_ } #_ }->($hash);
output
value

Answer 3

I assume none of the nested hashes have more than a single element?
A simple iteration is all that's necessary
use strict;
use warnings;
use 5.010;
my #hashes = (
{ 'known' => { 'a' => { 'b' => 'value1' } } },
{ 'known' => { 'a' => { 'b' => { 'c' => 'value2' } } } },
{ 'known' => { 'a' => { 'b' => { 'c' => { 'd' => 'value3' } } } } },
);
say get_value($_) for #hashes;
sub get_value {
my ($hash) = #_;
($hash) = values %$hash while ref $hash eq 'HASH';
$hash;
}
output
value1
value2
value3