Your code:

my %filter_map = ( ... );

my $filter = q{};
if ($filter_clean) {

    my @filter_split = split //, $filter_clean;

    for my $fc (@filter_split) {
        if ( $fc =~ /\d/ ) {
            $filter .= $fc;
        }
        else {
            $filter .= $filter_map{ uc $fc };
        }
    }
}

say $filter;
[download]

Simpler procedural code:

my %map = ( ... );
$map{$_} = $_ for 0..9;

my $numeric;
for (split //, uc($word)) {
    $numeric .= $map{$_};
}

say $numeric;
[download]

Simpler functional code:

my %map = ( ... );
$map{$_} = $_ for 0..9;

my $numeric =
    join '',
     map $map{$_}, 
      split //, uc($word);

say $numeric;
[download]

In this case, both the procedural and function approach are quite clear.

It's very ironic that you're calling map unclear when your variable name indicates you're thinking in terms of a map.

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