# Change these to the actual column widths. Use a star at the end to get the rest.
my @column_widths = (###, ###, '*');
my $unpack_spec = join ' ', map { "A$_" } @column_widths;

my %codes;
while (<IN_FILE>)
{
    chomp;
    my ($desc, $code, $other_thingy) = unpack $unpack_spec, $_;

    # If you want to remove the pre-pended whitespace on the description ...
    $desc =~ s/^\s+//;

    $codes{$code} = {
        Description => $desc,
        Other_Thing => $other_thingy,
    };
}

my $choice = 'GMT';
print "$choice: $codes{$choice}{Description}\n";