use strict;
use Data::Dumper;

my $x = { a => 1, b => 2, aa => { aaa => 11 } };
print Dumper($x);

my $y = { c => 3, d => 4, aa => { bbb => 11 } };
print Dumper($y);

$x = { %$x, %$y };
print Dumper($x);
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$VAR1 = { 'c' => 3,
          'a' => 1,
          'b' => 2,
          'd' => 4,
          'aa' => {
                    'bbb' => 11
                  }
        };
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use Hash-Dumper qw/merge/;
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$x = { %$x, %$y };
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$x = merge( $x, $y );
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$VAR1 = {
          'c' => 3,
          'a' => 1,
          'b' => 2,
          'd' => 4,
          'aa' => {
                    'bbb' => 11,
                    'aaa' => 11
                  }
        };
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> But this goes only one level deep.

Of course!

Since there are many possible interpretations of what a "deep merge" should do, you should script it in a recursive way after your well defined needs.¹

Cheers Rolf

_{(addicted to the Perl Programming Language and ☆☆☆☆ :)}

update

see also how to merge hash deeply ?

¹) for example what do you expect to happen if both hashes have the same scalar entry?

 
%a = (x=>1}; 
%b = (x=>2);
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Thank you

Note that the above is *really* inefficient (or at least it was). You might consider:  @hash1{ keys %hash2 } = values %hash2; Which is more efficient.