Here's some fun; reverse the string and the regex in the statement, eg.:

if   ( ""    =~ /^\Q$answer/i ) { default()     }
elsif( "YES" =~ /^\Q$answer/i ) { affirmative() }
elsif( "NO"  =~ /^\Q$answer/i ) { negative()    }
[download]

Now the user can type "y", "ye" or "yes".

Or if you want you can build a case statement:

SWITCH: {
    $answer =~ /^yes|y$/ && do { affirmative(); last SWITCH; };
    $answer =~ /^no|n$/  && do { negative(); last SWITCH;    };
    default();
}
[download]