Programming Notes ($Id$)

* Every command that can used on the command line lives in either this
  directory ('cmd') or in a local version ('local_cmd'). You are cajoled or
  ordered not to and generally discouraged from altering the commands in
  the 'cmd' directory. You can put local copies in the 'local_cmd' directory
  and they will override the standard ones.

* If you want to play, do it in the 'local_cmd' directory. It's very easy and
  reasonably safe. You can override a command whilst the cluster is running. 
  Compilation errors will simply give you error messages, it won't stop the
  cluster running - this only happens if you mess with the internals to the
  extent that it gets confused...

* A command is a piece of perl, it is simply a small snippet of program
  that is dynamically loaded into the cluster on invocation from the 
  command line. The last modification time is used to determine whether to
  reload it.

* New (or altered) commands are available for test the moment you save them.

* A command is placed into the appropriate directory with a '.pl' appended
  to the end. So the 'show/qra' command lives in 'cmd/show/qra.pl' (or a
  local version would be in 'local_cmd/show/qra.pl'.

* For the security conscious, potentially dubious characters (i.e. not 
  [A-Za-z0-9_/]) are converted to their hex equivalents. This will almost
  certainly mean that the user will get an error message (unless you have
  your secret squirrel hat on and have deliberately put such commands up 
  [in 'local_cmd' of course]).

* The snippets of program you put here are wrapped in an eval { } and
  are subroutines derived from the DXChannel class. They effectively
  the following declaration :-

  sub Emb_<cmdname>($self, $args)
  {
     ...
     your code here
     ...
  }

* slash characters are replaced by '_' so the equivalent name for 'show/qth'
  is 'Emb_show_qth'.

* you would normally do a 'my ($self, $line) = @_;' as the first thing. There
  are a complete set of accessors for DXUser, DXCommandmode and DXChannel
  classes and these are the recommended way of getting at these classes.
  A fairly standard start might be:-

  my ($self, $line) = @_;
  @args = split /\s+/, $line;
  $call = $self->call;
  $user = $self->user;

* $args is the rest of the line after the command (as a string).

* You are responsible for maintaining user security. If you have a command
  that does something a normal system shouldn't be allowed to do or see, 
  there is $self->priv (using the above example) which gives you the running
  privilege level of the channel. USE IT!

* The normal privilege levels are:-
    0 - user privilege.
    5 - sysop privilege.
    9 - console privilege.

  The sysop privilege is for things that you are prepared for remote
  sysops and clusters to do or see.

  A console privilege can only be executed locally (at least if you have
  correctly installed the client program in inetd or ax25d).

  The set/priv command can only be executed by a console privileged 
  session.

* You must return a list with a 0 or 1 as the first element. 1 means
  success and 0 means fail. Each element of the list which follows is 
  assumed to be one line for output. Don't put \n characters at the end
  of an element (the client will put the correct one in if required 
  [but see below]).

* As this is perl and it is very easy to alter stuff to get it correct,
  I would like to see some intelligent argument processing, e.g. if 
  you can have one callsign, you can have several. Interpret your
  arguments; so for example:-

    set/locator jo02lq       - sets your own locator to JO02LQ
    set/locator g1tlh jo02lq - sets G1TLH's locator (if you are allowed)

  or

    show/locator             - displays your locator (and other info?)
    show/locator in92jo      - displays the bearing and distance to 
                               IN92JO using your lat/long or locator
    show/locator jn56in in92jo  - bearing and distance between two
                                  locators
    show/locator gb7dxc      - bearing and distance to gb7dxc if poss.  

* It is important that you remember when you have tie hashes using MLDBM
  et al. If you do a DXUser->get($call) you will get a different (older)
  thing than the one in $self->$user. This is almost certainly NOT what
  you want if want to modify a user that is currently connected.

* Anything you output with a > as the last character is taken to mean
  that this is a prompt and will not have a \r or \n appended to it.

* help files can also be placed in the appropriate place. These files 
  have exactly the same naming conventions as commands except that they
  have a '.hlp' appended to the command name rather than a '.pl'. All 
  in the help file are sent to the user except those starting with a '#'
  character.