use warnings;
use strict;

my %formal_name = (
    bill => 'william',
    will => 'william',
    abe  => 'abraham'
);

print_formal_name('will');
print_formal_name('sam');
print_all_nicknames('wiLLiam');
print_all_nicknames('thomas');

sub print_formal_name {
    my $nickname = shift;
    if (exists $formal_name{lc $nickname}) {
        print "The formal name for $nickname is ", ucfirst $formal_name{lc $nickname}, ".\n";
    }
    else {
        print "There is no formal name for $nickname.\n";
    }
}
sub print_all_nicknames {
    my $formalname = shift;
    my @nicknames;
    for my $nickname (keys %formal_name) {
        if ($formal_name{$nickname} eq lc $formalname) {
            push @nicknames, ucfirst $nickname . ', ';
        }
    }
    if (@nicknames) {
        $nicknames[$#nicknames] =~ s/, //;
        print ucfirst lc $formalname, " has these nicknames: ", @nicknames, ".\n";
    }
    else {
        print ucfirst lc $formalname, " has no nicknames.\n";
    }
}

##</code><code>##

The formal name for will is William.
There is no formal name for sam.
William has these nicknames: Will, Bill.
Thomas has no nicknames.