Question

I am trying to iterate over items in the data structure that uses nested hash.
To do so, I wanted to see what keys are in there.

The following is what I have tried. But I am getting an error

    my %tgs = (
        'articles' =>  {
                           'vim' => 'about vim',
                           'awk' => 'about awk',
                           'sed' => 'about sed'
                       },
        'ebooks'   =>  {
                           'linux 101'    => 'about linux',
                       }
    );

    foreach my $k (keys %tgs){
        print $k;
        print "\n";
        foreach my $k2 (keys %$tgs{$k}){ #<-----this is where perl is having a problem
            print $k2;
            print "\n";
        }
    }

syntax error at PATH line #, near "$tgs{"
syntax error at PATH line #, near "}"
Execution of PATH aborted due to compilation errors.

What’s is wrong with my approach? My reasoning was since $tgs{$k} returns the reference of hash, I could dereference it in for each loop, but I guess not?

Answer 1

You need braces around $tgs{$k}:

foreach my $k2 (keys %{$tgs{$k}}){ #<-----this is where perl is having a problem

The full code would be:

foreach my $k1 (keys %tgs){
    print "Key level 1: $k1\n";
    foreach my $k2 (keys %{$tgs{$k1}}) {
        print "    Key level 2: $k2\n";
    }
}