Perl How to build a Dynamic multi level hash lookup - perl

Question

I have a code block that i use many times with slight variations that i am trying to make into a subroutine.
This code block Completes configuration templates ( router interface, vrf, other network stuff)
It does so by looking up data in a hash data structure ( called %config_hash) that is built from ingesting a excel file :P. The data that is looked up is in different areas of the hash for different templates.
an example of the current working code is this:
my #temp_source_template = #{ clone ($source_template{$switch_int_template}) };
my %regex_replacements=(); ## hash for holding regex search and replace values, keys are !name! (look in template files) values taken from DCAP
my #regex_key =(); ## temp array used for whe more then one !name! on a line
my $find_string='';
foreach my $line (#temp_source_template){
my (#regex_key) = ( $line =~ /(\!.*?\!)/g ); ## match needs to be non greedy thus .*? not .*
foreach my $hash_refs (#regex_key){
my $lookup = $hash_refs =~ s/!//gri; ## remove ! from !name! so lookup can be done in DCAP file hash
my $excel_lookup = $lookup =~ s/_/ /gri;
$regex_replacements{$hash_refs} = $config_hash{'Vlan'}{$inner}{$excel_lookup}; ## lookup DCAP file hash a write value to regex hash
if (undef eq $regex_replacements{$hash_refs}){
$regex_replacements{$hash_refs} = $config_hash{'Switch'}{$outer}{$excel_lookup};
}
if (undef eq $regex_replacements{$hash_refs}){
$regex_replacements{$hash_refs} = $config_hash{'VRF'}{$middle}{$excel_lookup};
}
$find_string= $find_string . $hash_refs . '|' ;
}
}
So this creates a hash (regex_replacements) that contains values to lookup (hash keys in regex_replacements) and values to replace those with (values in regex_replacements). it also builds a string to be used in a regex expression ( $find_string). Different templates will have different hash lookup "paths" ( eg $config_hash{'Switch'}{$outer}{$excel_lookup} ) or in different orders (effectively a most specific match)
for completeness here is the code block that does the regex replacements:
foreach my $line (#temp_source_template){
my (#line_array) = split /(![A-Za-z_]*!)/, $line;
foreach my $chunk (#line_array){
my $temp_chunk = $chunk;
$chunk =~ s/($find_string)/$regex_replacements{$1}/gi;
if (!($chunk)){
$chunk = $temp_chunk;
}
}
$line = join ("", #line_array);
if ($line =~ /\!.*\!/){
print {$log} " ERROR line has unmatched variables deleting line \"$line\"\n";
$line ="";
}
}
So I did some searching and i found this:
Perl: How to turn array into nested hash keys
Which is almost exactly what i want but i can't get it to work because my Variable reference is a Hash and its hash variable reference is just "REF" so i get errors for trying to use a hash as a reference.
So I wont post what i have tried as i don't really understand the magic of that link.
But what i am doing is passing to the sub the following
my #temp_source_template = #{ clone ($source_template{$test}) };
my #search_array = ( ['VRF' ,$middle] , ['Switch' ,$outer]);
my $find_string, $completed_template = dynamic_regex_replace_fine_string_gen(\%source_config,\#temp_source_template, \#search_array);
and i want returned the $find_string and the regex_replacements hash ref. It should be noted that in the sub i need to append onto the end of the elements of #search array the value of $excel_lookup.
The bit that i dont understand how to do is build the variable level hash lookup.

Answer 1

You could try use Data::Diver it provides a simple access to elements of deeply nested structures.
For example:
use feature qw(say);
use strict;
use warnings;
use Data::Diver qw(Dive);
my $hash = { a => { b => 1, c => { d => 2 }}};
my $keys = [[ 'a', 'b'], ['a','c','d']];
lookup_keys( $hash, $keys );
sub lookup_keys {
my ( $hash, $keys ) = #_;
for my $key ( #$keys ) {
my $value = Dive( $hash, #$key );
say $value;
}
}
Output:
1
2
See Also:
Creating hash of hash dynamically in perl
Read config hash-like data into perl hash