$choice = lc $choice;

# ... later ...

if ($choice eq 'l')

##</code><code>##

my $filename = 'birthday.db';

# ... later ...

open IN, $filename || die "Cannot read '$filename': $!\n";
print <IN>;
close IN;

##</code><code>##

use constant CHOICE_LIST => 'l';
my $db_file = 'birthday.db';

# ... later ...

if ($choice eq CHOICE_LIST)
{
    open(IN, $db_file) || die "Cannot read '$db_file': $!\n";
    print <IN>;
    close IN;
}

##</code><code>##

if ($choice eq CHOICE_MODIFY)
{
    # Use a hash, not an array. The assumption here is that the names will be unique.
    open(IN, $db_file) || die "Cannot read '$db_file': $!\n";
    my %birthdays = map { chomp; split ':' } <IN>;
    close IN;

    # Print out a list of the names and birthdays
    print "$_ => $birthdays{$_}\n" for sort keys %birthdays;

    print "Enter record to modify: "; chomp ($key = <STDIN>);
    print "(M)odify or (D)elete? "; chomp ($choice = <STDIN>);

    $choice = lc $choice;
    if ($choice eq 'm')
    {
        print "Enter person's birthday: "; chomp ($date = <STDIN>);
        $birthdays{$key} = $date;
    }
    elsif ($choice eq 'd')
    {
        delete $birthdays{$key};
    }

    open OUT, $db_file || die "Cannot overwrite '$db_file': $!\n";
    print OUT "$_:$birthdays{$_}\n" for keys %birthdays;
    close OUT;
}