foreach my $host_num ( 0..num_hosts()-1 ) {
    print "[$host_num] ", hostname_by_num($host_num), "\n" ;
}

##</code><code>##

use Scalar::Util qw(looks_like_number);

sub hostname_by_num { 
    my $num = shift;

    # validate our argument
    defined $num
       or return undef;
    $num >= 1
       or return undef;
    looks_like_number( $num )
       or return undef;

    $num--;  # convert into array index.

    return exists $HOSTS[$num] ? $HOSTS[$num] : undef;
}

##</code><code>##

sub choose_host {
    my $chosen_host;
    while ( !defined $chosen_host ) {
        printchoices();
        $chosen_host = hostname_by_num( getchoice() );
    }

    return $chosen_host;
}

# for loop can now be:
sub printchoices {
    print join "\n",
        "\n",
        "ssh hosts",
        "-"x8;

    foreach my $host_num ( 1..num_hosts() ) {
        print "[$host_num] ", hostname_by_num($host_num), "\n" ;
    }
}


##</code><code>##

sub ssh_string {
    my $host = shift;
  
    return join '',
        username(),
        '@', 
        $host,
        domain();
}