http://www.perlmonks.org?node_id=196663

Answer to this node. Merges multiple hashes recursively.
Usage: $href = mergehashes(\%h1,%h2,%h3);
Keys' values are turned into an array ref. Any key that has a single non-ref value will be converted back to a scalar.
Dies on circular references. (This is a feature)
#!/usr/bin/perl -w use warnings; use strict; BEGIN { my %SeenMerged = (); sub mergehashes{ # Dies on circular references my @hashrefs = @_; die "Passed a non hashref" if grep { ref $_ ne 'HASH' } @h +ashrefs; my %merged = (); my @seen = grep { ref $_ eq 'HASH' } @SeenMerged{@hashref +s}; # Break circular links.. if (@seen){ die "contains a circular reference! bailing..."; } @SeenMerged{@hashrefs} = @hashrefs; foreach my $h (@hashrefs){ while (my ($k,$v) = each %$h ){ push @{$merged{$k}}, $v; } } while (my ($k,$v) = each %merged){ my @hashes = grep { ref $_ eq 'HASH' } @$v; $merged{$k} = $v->[0] if (@$v == 1 && !ref $v->[0]); + $merged{$k} = mergehashes(@hashes) if @hashes; } delete @SeenMerged{@hashrefs}; return \%merged; } }
# EXAMPLE

use Data::Dumper;

my (%hash1,%hash2);
%hash1 = (
          red => 1,
          brown => {
                    green => 1,
                    blue => {
                             yellow => 1,
                            },
                    black => 1,
                   },
          gray => 1,
		  
         );

%hash2 = (
          white => 1,
          brown => {
                    purple => 1,
                   },
         );



my $merged = mergehashes(\%hash1, \%hash2 );

print Dumper($merged);


__END__
outputs

$VAR1 = {
          'gray' => 1,
          'white' => 1,
          'brown' => {
                       'blue' => {
                                   'yellow' => 1
                                 },
                       'purple' => 1,
                       'green' => 1,
                       'black' => 1
                     },
          'red' => 1
        };

Replies are listed 'Best First'.
Re: Merge Multiple Hashes
by blakem (Monsignor) on Sep 10, 2002 at 18:02 UTC
Re: Merge Multiple Hashes
by Anonymous Monk on May 05, 2020 at 21:53 UTC
    thank you for the snippet, I really appreciate it.
    I found the need of handling arrays too: append them if found.
    to combine {a:[1,2]} and {a:[3,4]} into {a:[1,2,3,4]} I had to edit the while loop in the middle:
       while (my ($k,$v) = each %merged) {                                                      
         my @hashes = grep { ref $_ eq 'HASH' } @$v;
         #$merged{$k} = $v->[0] if (@$v == 1 && !ref $v->[0]);
    
         # append text separated with \n\n, but do not duplicate identical values
         $merged{$k} = join "\n\n", do { my %seen; grep {!$seen{$_}++} @$v} if (!ref $v->[0]);
    
         # append arrays one to other
         @{$merged{$k}} = map {@$_} @$v if (ref $v->[0] eq 'ARRAY');
    
         $merged{$k}  = mergehashes(@hashes) if @hashes;
       }
    
    I thought someone else will find this useful too.