#!/usr/bin/perl

use Data::Dumper;

%hash=(
    a=>1,
    b=>2,
    c=>3,
    aa=>4,
);

@filterd_keys=grep {/a/} keys %hash;

@filterd_hash{@filterd_keys}= @hash{ @filterd_keys };

print Dumper \%filterd_hash;

$VAR1 = {
          'a' => 1,
          'aa' => 4
        };

delete @hash{ grep !m/a/, keys %hash };

my %hash2 = map { m/a/ ? ($_, $hash{$_}) : () } keys %hash;

%hash2= map { ($_,$hash{$_}) }
          grep {/a/}
            keys %hash ;

Hash = { 'a': 1, 'b': 2, 'c': 3, 'aa': 4 }
Hash = dict([(k, v) for k, v in Hash.items() if re.compile(r'a').search(k)])