This is a module that might benefit from Sub::Exporter. It allows you to export custom functions that are tailored to the user's needs. Here are some usage examples:

use Business::CreditCard::Obscure qw(obscure);

print obscure('4444333322221111');  # 4444********1111

use Business::CreditCard::Obscure
    obscure => { head => 4, tail => -4, replacement => '!' };

print obscure('4444333322221111');  # 4444!!!!!!!!1111

use Business::CreditCard::Obscure
    obscure => { head => 4, -as => 'obscurevisa' },
    obscure => { head => 3, tail => -3, -as => 'obscurediner' };

print obscurevisa('4444333322221111');  # 4444********1111
print obscurediner('444333222111');  # 444******111
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And here is the code to implement the above examples:

package Business::CreditCard::Obscure;

use strict;
use warnings;

use Sub::Exporter
    -setup => {
      exports => [ obscure => \&build_obscure ]
    };

sub build_obscure {
  my ( $class, $name, $arg ) = @_;

  $arg->{head}        ||=  0;
  $arg->{tail}        ||= -4;
  $arg->{replacement} ||= '*';

  return sub {
    my $data = shift;
    substr( $data, $arg->{head}, $arg->{tail} )
        =~ s/./$arg->{replacement}/g;
    return $data;
  }
}

1;
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