Autovivification!

When you search for a path, if its depth is greater than 1, your main data under search will grow, and that's exactly why your program will not stop.

Now I think it is your duty to fix it.

I added some debug info at certain key points, to reveal that your data is growing itself, see my inline comments: (Run it and watch the chain of foo->{foo}->{foo}->...->{})

use Data::Dumper;

sub rec_data {
    my $path = shift; # ->{foo}->{bar}
    my $data = shift; # nested perl structure
    my $data_main = shift;
    print Dumper($data_main);#let's see the fact
    my @results;
    
    # nothing to search
    return unless ref $data;

    # stop the evals complaining
    no warnings 'all';
    
    if (ref $data eq 'HASH') {
        foreach my $k (keys %$data) {
            my $ref = qq|\$data->{$k}$path|;
            if (my $val = eval($ref)) {
                push @results, ref($val) ? $val : eval "\\$ref";
            }
            
            if (ref $data->{$k}) {
                print "calling from entry point1, k = $k\n";
                push @results, rec_data($path, $data->{$k}, $data_main
+);#just pass the third parameter along without change(?)
            }
        }
    }
    elsif (ref $data eq 'ARRAY') {
        foreach my $k (@$data) {
            my $ref = qq|\$k$path|;
            if (my $val = eval($ref)) {
                push @results, ref($val) ? $val : eval "\\$ref";
            }
            
            if (ref $k) {
                print "calling from entry point2\n";
                push @results, rec_data($path, $k, $data_main);
            }
        }
    }

    return @results;
}


my $data_main = {
    test  => { 
        foo => { bar => 'bar', baz => 'baz' },
        bar => { baz => 'baz' } ,
    }
};

my @results = rec_data('->{foo}->{bar}', $data_main, $data_main);#The 
+program should never change the third parameter, is that true?
print Dumper(\@results);
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