Question

Let’s assume that I have a complex hash reference $hash_ref, and I would like to access data in it by doing something like this:

my $string1 = "{books}";
my $string2 = "{31335}->{book_name}";
print Dumper($hash_ref->$string1->$string2);

Of course, this doesn’t work, but I hope it explains what I’d like to do.

Obviously, there are many ways I can make this work, but I am (out of curiosity) really interested to figure out if there is some Perl magic that could make this work without splitting strings, etc.

I know that I could create 3 strings ("books", "31335", "book_name") and have this done in a second, and there are certainly other ways, but I never understood if one could actually access hash data by using strings that represent hash structure, like in the above example.

Thanks 🙂

Answer 1

It can be done using eval. However, just because some can be done doesn’t mean it should.

use strict;
use warnings;

my $hr = { books => { 31335 => { book_name => 'FOO' } } };

my $k1 = "{books}";
my $k2 = "{31335}->{book_name}";

my $f = eval "\$hr->$k1->$k2";  # Don't do this. It's a terrible idea.
print $f, "\n";                 # FOO

You should bite the bullet and extract the keys from the strings:

my @ks = "$k1$k2" =~ /\{ \s* (.+?) \s* \}/gx;
$f = $hr;
$f = $f->{$_} for @ks;
print $f, "\n";                 # FOO