use strict;
use warnings;

$|++;

my %acro = (
    HTML   => "Hypertext Markup Language",
    ICBM   => "Intercontinental Ballistic Missile",
    EEPROM => "Electronically-erasable programmable read only memory",
    SCUBA  => "Self Contained Underwater Breathing Aparatus",
    FAQ    => "Frequently Asked Questions",
    LCARS  => "Library Computer And Retrieval System",
    NASA   => "National Aeronautical and Space Administration",
);

INPUT: {
    print "Please enter an acronym: ";
    chomp( $_ = <STDIN> );
    $_ = uc or redo INPUT;

    last INPUT if /^Q/;

    unless (exists $acro{$_})
    {
        print "I don't know what '$_' means.\n";
        redo INPUT;
    }

    print "$_ ($acro{$_})\n";
    redo INPUT;
}