$ perl -MData::Dumper -E '
> $text = q{a 2 b 4,5,6 c d e 45,657,-67};
> %hash =
>    map { $_->[ 0 ] => [ split m{,}, $_->[ 1 ] ] }
>    sub {
>        push @arr, [ $1, $2 ]
>           while $_[ 0 ] =~ m{\s*([a-z])\s+([-,\d]*)}g;
>        return @arr;
>        }->( $text );
> say Data::Dumper->Dumpxs( [ \ %hash ], [ qw{ *hash } ] );'
%hash = (
          'e' => [
                   '45',
                   '657',
                   '-67'
                 ],
          'c' => [],
          'a' => [
                   '2'
                 ],
          'b' => [
                   '4',
                   '5',
                   '6'
                 ],
          'd' => []
        );
$