# Untested
my @filesize_names = qw(kilobyte megabyte gigabyte terabyte petabyte exabyte zettabyte yottabyte);
my %short_sizes = map { m/^(\w)/; $1 . 'b' => $_ } @filesize_names;
my $word = 'kb';
if ( exists $short_sizes{lc $word} ) {
    say $short_sizes{lc $word};
}