use strict;
use Data::Dumper;

my %hash1 = (
        key1 => 'relative_path',
        key2 => {
                key21 => 'another_relative_path',
                key22 => '/an_absolute_path',
                key23 => 'relative_path',
        },
        key3 => '',
        key4 => 4
);

my @paths = ('key1', 'key2:key22', 'key2:key23');

for my $path (@paths) {
   my @path = split(/:/, $path);
   my $val = dive(\%hash1, @path);
   warn $val;
}

sub dive {
   my $r = shift;
   $r = $r->{shift(@_)} while $r && @_;
   return $r;
}